DISSOLUTION AND ABSORPTION ENHANCEMENT OF POORLY … · 2016-08-29 · provided the lowest mean...
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DISSOLUTION AND ABSORPTION ENHANCEMENT OF POORLY WATER-SOLUBLE DRUGS USING SOLID SELF-EMULSIFYING DRUG DELIVERY SYSTEM By Mr. Yotsanan Weerapol A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Program in Pharmaceutical Technology Graduate School, Silpakorn University Academic Year 2014 Copyright of Graduate School, Silpakorn University
Transcript of DISSOLUTION AND ABSORPTION ENHANCEMENT OF POORLY … · 2016-08-29 · provided the lowest mean...
DISSOLUTION AND ABSORPTION ENHANCEMENT OF POORLY WATER-SOLUBLE DRUGS USING SOLID SELF-EMULSIFYING DRUG
DELIVERY SYSTEM
By
Mr. Yotsanan Weerapol
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree
Doctor of Philosophy Program in Pharmaceutical Technology
Graduate School, Silpakorn University
Academic Year 2014
Copyright of Graduate School, Silpakorn University
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DISSOLUTION AND ABSORPTION ENHANCEMENT OF POORLY WATER-SOLUBLE DRUGS USING SOLID SELF-EMULSIFYING DRUG
DELIVERY SYSTEM
By
Mr.Yotsanan Weerapol
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree
Doctor of Philosophy Program in Pharmaceutical Technology
Graduate School, Silpakorn University
Academic Year 2014
Copyright of Graduate School, Silpakorn University
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การเพมการละลายยาและการดดซมยาละลายนายากโดยใชระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขง
โดย
นาย ยศนนท วระพล
วทยานพนธนเปนสวนหนงของการศกษาตามหลกสตรปรญญาเภสชศาสตรดษฎบณฑต สาขาวชาเทคโนโลยเภสชกรรม
บณฑตวทยาลย มหาวทยาลยศลปากร ปการศกษา ๒๕๕๗
ลขสทธของบณฑตวทยาลย มหาวทยาลยศลปากร
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The Graduate School, Silpakorn University has approved and accredited the
Thesis title of “Dissolution and absorption enhancement of poorly water-soluble drugs
using solid self-emulsifying drug delivery system” submitted by Mr.Yotsanan
Weerapol as a partial fulfillment of the requirements for the degree of Doctor of
Philosophy in Pharmaceutical Technology.
…………...................................................................... (Associate Professor Panjai Tantatsanawong,Ph.D.)
Dean of Graduate School ........../..................../..........
The Thesis Advisor
1. Professor Pornsak Sriamornsak, Ph.D. 2. Associate Professor Sontaya Limmatvapirat, Ph.D.
The Thesis Examination Committee …………….......................................... Chairman (Associate Professor Prasert Akkaramongkolporn, Ph.D) ............/......................../.............. .............................................................. Member (Professor Mont Kumpugdee Vollrath, Ph.D.) ............/......................../.............. .............................................................. Member (Associate Professor Srisagul Sungthongjeen, Ph.D.) ............/......................../.............. .............................................................. Member (Professor Pornsak Sriamornsak, Ph.D) ............/......................../.............. .............................................................. Member (Associate Professor Sontaya Limmatvapirat, Ph.D.) ............/......................../..............
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51353805 : MAJOR : PHARMACEUTICAL TECHNOLOGY KEYWORD : NIFEDIPINE/ SELF-EMULSIFYING DRUG DELIVERY SYSTEM/ POORLY
WATER-SOLUBLE DRUG YOTSANAN WEERAPOL : DISSOLUTION AND ABSORPTION ENHANCEMENT
OF POORLY WATER-SOLUBLE DRUGS USING SOLID SELF-EMULSIFYING DRUG DELIVERY SYSTEM. THESIS ADVISOR : PROF. PORNSAK SRIAMORNSAK, Ph.D. AND ASSOC. PROF. SONTAYA LIMMATVAPIRAT, Ph.D. 139 pp.
The low solubility of poorly water-soluble drug is a major problem of oral drug adsorption. The self-emulsifying drug delivery system (SEDDS) can be applied to eliminate drug dissolution step and improve drug absorption. A mixed surfactant system was designed to fabricate SEDDS based on hydrophilic-lipophilic balance (HLB) value and ternary phase diagram. Nifedipine (NDP) was used as a model drug. The impact of HLB and molecular structure of surfactants on the formation of SEDDS was investigated. The selected surfactants were then used to formulate SEDDS by construction of ternary phase diagram. The solid SEDDS was developed by adsorbing on the solid carriers, e.g., fumed silica, porous silicon dioxide and porous calcium silicate. The influence of solid carrier properties such as porosity and surface area on drug dissolution was evaluated. The pharmacokinetics of NDP in different formulations were also investigated. The results showed that, in the SEDDS formulation based on HLB value, droplet size of emulsions obtained after diluting SEDDS in aqueous medium was independent of the HLB of a mixed surfactant. Structure of surfactant was found to influence the emulsion droplet size. The concentration and composition in SEDDS formulations were great importance for the self-emulsification when using ternary phase diagram. The region in ternary phase diagram giving the SEDDS with emulsion droplet size of less than 300 nm after diluting in aqueous medium was selected for further investigation. The small angle X-ray scattering curves showed no sharp peak after dilution at different percentages of water, suggesting non-ordered structure. In vitro dissolution study showed an increase in dissolution of NDP from SEDDS formulations, compared to NDP powders. The solid SEDDS was prepared by adsorbing onto solid carriers; porous calcium silicate at 50% provided a free-flowing powder with the highest drug dissolution. The porous properties of calcium silicate also provided the lowest mean dissolution time. The pharmacokinetics of drug in Wistar rats showed that the solid SEDDS containing porous calcium silicate attributed to a significant increase of NDP in plasma. In the fasted rats, the Cmax of SEDDS and solid SEDDS using porous calcium silicate was 1857.8±585.5 and 2367.9±113.6 ng/mL, respectively. The AUC of SEDDS and solid SEDDS containing porous calcium silicate was found to be higher than NDP powder for 2.9 and 7.1 times, respectively. Similar results were found in fed rats. Other poorly water-soluble drugs, i.e., felodipine (FDP), manidipine (MDP) and itraconazole (ITZ), were also applied in the selected solid SEDDS formulations. The difference in lipophilicity of drug affected the drug dissolution from solid SEDDS loaded with NDP, FDP, MDP and ITZ, providing the linear relationship between lipophilicity and percent drug dissolved. The solid SEDDS provided the high drug dissolution (> 80% in 60 min). It is suggested that the developed solid SEDDS can be applied for various types of poorly water-soluble drugs to enhance the dissolution. In summary, the dissolution and absorption enhancement of poorly water-soluble drug could be achieved in this study by using solid SEDDS.
Program of Pharmaceutical Technology Graduated School, Silpakorn University Student‘s signature…………………………………………….…………………. Academic year 2014 Thesis Advisor’s signature 1. …………………………………….. 2. …………………..………………..
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51353805 : สาขาวชาเทคโนโลยเภสชกรรม คาสาคญ : ไนเฟดพน/ ระบบนาสงยาชนดเกดอมลชนไดเอง/ ยาละลายนายาก
ยศนนท วระพล : การเพมการละลายยาและการดดซมยาละลายนายากโดยใชระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขง. อาจารยทปรกษาวทยานพนธ : ศ. ดร. พรศกด ศรอมรศกด และ รศ. ดร. สนทยา ลมมทวาภรต. 139 หนา.
ยาละลายนายากมคาการละลายของยาในนาตาเปนปญหาสาคญของการดดซมยาเขาสกระแสเลอดเมอใหยาดวยการรบประทาน ระบบนาสงยาชนดเกดอมลชนไดเองสามารถลดขนตอนการละลายยาซงชวยเพมการดดซมยาได ระบบสารลดแรงตงผวผสมถกนามาใชเปนระบบนาสงยาชนดเกดอมลชนไดเองโดยอาศยคา hydrophilic-lipophilic balance (HLB) ในงานวจยนใชยา ไนเฟดปนเปนยาตนแบบโดยศกษาผลของคา HLB และโครงสรางโมเลกลของสารลดแรงตงผวตอการตงตารบระบบนาสงยาชนดเกดอมลชนไดเอง นาสารลดแรงตงผวทคดเลอกไวมาสรางแผนภาพวฏภาคไตรภาค พฒนาระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงโดยดดซบอยบนตวพาของแขง เชน ฟมซลกา ซลกอนไดออกไซดแบบมรพรนและแคลเซยมซลเกตแบบมรพรน ศกษาอทธพลของสมบตของตวพาของแขง เชน ความพรนและพนทผว ตอการละลายของยาและศกษาเภสชจลนศาสตรของยาในตารบตางๆ ผลการศกษาพบวาการตงตารบระบบนาสงยาชนดเกดอมลชนไดเองโดยอาศยคา HLB นน ขนาดอมลชนหลงจากเจอจางในนาไมขนกบคา HLB ของสารลดแรงตงผวผสม โครงสรางของสารลดแรงตงผวสงผลตอขนาดของอมลชน ความเขมขนและองคประกอบในระบบนาสงยาชนดเกดอมลชนไดเองสงผลตอการเกดเปนอมลชนไดเองเมอเตรยมโดยใชแผนภาพวฏภาคไตรภาค บรเวณในแผนภาพวฏภาคไตรภาคทใหอมลชนขนาดเลกกวา 300 นาโนเมตรหลงเจอจางในนาถกนาไปศกษาตอ ผลการกระเจงรงสเอกซทมมเลกไมพบพคหลงจากเจอจางระบบนาสงยาชนดอมลชนเกดไดเองในนาทสดสวนตางๆ กน แสดงวามการจดเรยงตวไมเปนระเบยบ การศกษาการละลายของยาแสดงใหเหนการเพมการละลายของยาไนเฟดปนจากระบบนาสงยาชนดเกดอมลชนไดเองเมอเทยบกบผงยาไนเฟดปน ระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงเตรยมขนโดยการดดซบบนตวพาของแขงและเมอใชแคลเซยมซลเกตแบบมรพรนในปรมาณรอยละ 50 ทาใหไดตารบมลกษณะเปนผงมการไหลดและมการละลายยาสงทสด สมบตความพรนของแคลเซยมซลเกตยงใหคาเฉลยการละลายยาตาทสด การศกษาเภสชจลนศาสตรในหนขาวใหญพบวาระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงทมแคลเซยมซลเกตแบบมรพรนเพมปรมาณไนเฟดปนในกระแสเลอดอยางมนยสาคญ ในสภาวะอดอาหารพบวาความเขมขนของยาสงสดในกระแสเลอดของระบบนาสงยาชนดเกดอมลชนไดเองและระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงทใชแคลเซยมซลเกตแบบมรพรนมคา 1857.8 ± 585.5 และ 2367.9 ± 113.6 นาโนกรมตอมลลลตร ตามลาดบ คาพนทใตกราฟของระบบนาสงยาชนดเกดอมลชนไดเองและระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงมคามากกวาผงยาไนเฟดพน 2.9 และ 7.1 เทา ตามลาดบ การศกษาในสภาวะไดรบอาหารไดผลการทดลองคลายกน การนายาละลายนายาก ชนดอน ไดแก เฟโลดพน มานดพนและไอทราโคนาโซล มาประยกตใชทดสอบกบตารบทไดพฒนาขน พบวาความแตกตางในการชอบไขมนของยามความสมพนธตอการละลายของยาจากระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงโดยมความสมพนธแบบเสนตรงระหวางความชอบไขมนและคาการละลายยาทเวลา นาท ระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขงใหคาการละลายยาไดสง (มากกวา 80% ใน 60 นาท) ดงนนตารบทพฒนาขนสามารถประยกตใชกบยาละลายนายากชนดอนได โดยสรป ในการศกษานการเพมการละลายยาและการดดซมของยาละลายนายากสามารถทาไดโดยการใชระบบนาสงยาชนดเกดอมลชนไดเองชนดของแขง ________________________________________________________________________________________________________ สาขาวชาเทคโนโลยเภสชกรรม บณทตวทยาลย มหาวทยาลยศลปากร ลายมอชอนกศกษา………………………………………………………………………………..……………..…. ปการศกษา 2557 ลายมอชออาจารยทปรกษาวทยานพนธ 1. ………………….…….………..…..…….. 2. ………………..………………..….………
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ACKNOWLEDGEMENTS
Firstly, I would like to sincerely express my deepest gratitude to Professor Dr. Pornsak Sriamornsak, the thesis advisor of mine, for his supervision, advice and practical guidance of all these years. He provides me pleasant opportunities, patient encouragement and continual support in various ways. Not only does he always dedicate his time and interest in the discussions, but also shares the great attitude in my research. Appreciating his tremendous effort, I certainly much owe a debt of gratitude to him.
I would like to especially thank Associate Professor Dr. Sontaya Limmatavapirat, my thesis co-advisor for valuable advices and kindly supports throughout my work at the Pharmaceutical Biopolymer Group (PBiG), Faculty of Pharmacy, Silpakorn University.
I gratefully acknowledge Professor Dr. Mont Kumpugdee-Vollrath for her valuable advices and supports throughout my works at University of Applied Sciences (BHT), Berlin, Germany. Apart from her precious suggestions in laboratory studies, she does also advocate my living in Germany. Throughout both livelihood and work, the portentous experiences are given by this honorable supporter.
I am much obliged to Professor Dr. Hirofumi Takeuchi for his dedication to giving me assistance at Laboratory of Pharmaceutical Engineering, Gifu Pharmaceutical University, Japan. Aside from the worthy guidance and advice, his encouragement as well as concern during the time that I was a member of his laboratory will be memorable.
I especially thank to Associate Professor Dr. Jurairat Nunthanid, Associate Professor Dr. Manee Luangtana-anan, and Assistant Professor Dr. Panida Asavapichayont at the Pharmaceutical Biopolymer Group (PBiG), Faculty of Pharmacy, Silpakorn University, for their innumerably supportive things and useful suggestions toward my research.
I wish to acknowledge the Thailand Research Fund through, the Royal Golden Jubilee Ph.D. Program (grant number PHD/0346/2550). The authors gratefully acknowledge the financial support of the Graduate School, Silpakorn University.
I especially acknowledged Srisuda Konthong and Tassanee Nernplod, who help me in some of the in vitro dissolution tests and drug content analysis in this thesis.
I also would like to pass the special thanks to my parents, family and friends who always help and encourage me all along. The success is unreachable unless there is their love, fondness, and good care. Finally, I whole-heartedly appreciate everybody who is important to the thesis’ successful realization, as well as apologize for those whom I miss to mention personally.
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Table of Contents
Page
English Abstract…………………………………………………………………………………… iv
Thai Abstract………………………………………………………………………………….…… v
Acknowledgments…………………………………………………………………………….…… vi
List of Tables………………………………………………………………………………….…… ix
List of Figures………………………………………………………………………………….….. x
List of Abbreviations………………………………………………………………………….…… xii
Chapter
1 Introduction………………………………………………………………………………..…. 1
2 Literature review………………………………………………………………………….….. 4
Poorly water-soluble drug……………………………………………………………. 5
Self-emulsifying drug delivery system (SEDDS) ………………………………..….. 6
Excipients for SEDDS…………………………………………………………….…. 9
Mechanism of self-emulsification……………………………………………….…… 15
Formulation of SEDDS………………………………………………………………. 16
Evaluation of SEDDS……………………………………………………………….... 24
3 Formulation of SEDDS based on HLB value ………………………………………………… 30
Introduction…………………………………………………………………………... 31
Materials and methods ………………………………………………………….……. 32
Results and discussion…………………………………………………………….…. 38
Conclusion………………………………………………………………………….... 52
4 Formulation of SEDDS based on ternary phase diagram ……………………………………. 53
Introduction………………………………………………………………………..…. 54
Materials and methods …………………………………………………………….…. 55
Results and discussion……………………………………………………………….. 58
Conclusion………………………………………………………………….……….. 67
5 Effect of solid carrier on drug dissolution from solid SEDDS.……………..………….....… 68
Introduction…………………………………………………………………………. 69
Materials and methods …………………………………………………………….… 70
Results and discussion…………………………………………………………….… 75
Conclusion……………………………………………………………………..……. 96
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Chapter Page
6 Effect of dietary state on oral bioavailability of nifedipine by SEDDS: Effect of dietary state 97
Introduction…………………………………………………………………………… 98
Materials and methods ………………………………………………………………… 99
Results and discussion………………………………………………………………… 101
Conclusion……………………………………………………………………….…… 105
7 Effect of drug lipophilicity on dissolution of drug-loaded solid SEDDS……………………… 106
Introduction…………………………………………………………………….……… 107
Materials and methods ………………………………………………………………… 108
Results and discussion………………………………………………………………… 110
Conclusion……………………………………………………………………….……. 118
8 Summary and general conclusion………………………………………………………..…… 119
References ………………………………………………………………………………………… 122
Biography…………………………………………………………………………………………… 137
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List of Tables
Tables Page
2.1 Lipid formulation classification system: characteristic features, advantages and
disadvantages of the four essential types of lipid-based formulations.……..…… 7
2.2 Vegetable oil in pharmacopoeia.……………………………..……………………… 11
2.3 Animal fats and oil in pharmacopoeia.……………………….……………………… 12
2.4 Example of SEDDS studies, prepared by HLB calculation technique or ternary phase
diagram …………………………………………………………………………. 18
3.1 Ratio of mixed surfactants used in the formulations prepared at various HLB values 35
3.2 Composition SEDDS and solid SEDDS formulation……………………………….. 37
3.3 Solubility of nifedipine in various vehicles………………………………………… 39
3.4 Droplet size of SEDDS using a mixed surfactant of P40/ sorbitan monooleate,
prepared at HLB 10, after dispersion in water…………………………..….…… 45
3.5 Dissolution of nifedipine in SGF, after 20 and 120 min………………………..…… 52
4.1 Solubility of NDP in different formulations of SEDDS………………………..…… 61
4.2 Droplet size of SEDDS after diluting (199 folds) in water and SGF…………….…. 63
4.3 Droplet size after dilution various amount of water…………………………………. 64
5.1 Properties of solid carriers used in this study……………………………………….. 71
5.2 Composition of SEDDS and solid SEDDS formulations…………………………… 72
5.3 The angle of repose of solid SEDDS formulations using different solid carriers at
concentration of 20-50%........................................................................................ 76
5.4 Surface free energies of solid carriers and solid SEDDS formulations……………… 82
5.5 Emulsion droplet size of SEDDS and solid SEDDS formulations after diluting in
water or SGF………………………………………………………………………. 88
5.6 Mean dissolution time of SEDDS and solid SEDDS using several types of solid
carrier at 50% in the formulations and containing P35 or P40…………………… 91
5.7 Stability test results of selected SEDDS and solid SEDDS formulations containing
P35………………………………………………………………………………… 93
6.1 The composition of SEDDS and solid SEDDS formulations…………………..……... 99
6.2 Pharmacokinetic parameters of SEDDS and solid SEDDS formulations in the fasted
and fed conditions in vivo…………………………………………….……………103
7.1 Emulsion droplet size of SEDDS and solid SEDDS loading with different drugs,
diluted in water or SGF …………….……………………………………………… 112
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List of Figures Figure Page
2.1 The advantage of SEDDS in oral drug absorption.……………………………....… 8
3.1 Chemical structure of oil and surfactants investigated in this study………….…..... 33
3.2 Droplet size of emulsions containing CCG and polyoxyls/sorbitan monoester system
(ratio of 1:1) ……………………………………….………………...………... 42
3.3 Droplet size of emulsions containing CCG and polysorbate/sorbitan monoester
system (ratio of 1:1) ………………………………………………………….… 43
3.4 Schematic representation of the micellar configuration into oil-in-water (nano)
emulsion containing polyoxyls/sorbitan monooleate, polyoxyls/sorbitan
monolaurate, and polysorbate/sorbitan monooleate…………...……..……....... 45
3.5 SEM images of FS200, FSR, solid SEDDS containing 40% FS200, and solid
SEDDS containing 40% FSR…………………...……...…………………..…... 47
3.6 DSC thermograms of NDP, physical mixture, SEDDS and solid SEDDS formulation
containing P40 and sorbitan monooleate.………………..………………………… 48
3.7 Powder X-ray diffractograms of NDP, physical mixture, SEDDS and solid SEDDS
formulations containing P40 and sorbitan monooleate…………………………… 49
3.8 Percentage of NDP released from different formulations, in simulated gastric fluid
USP without pepsin, at 37oC. ……………………………………………………… 51
4.1 Ternary phase diagram composing of CCG, P40 and DGE, CCG, P35and DGE….… 59
4.2 Ternary phase diagram showing the SEDDS formulations loading with NDP………. 60
4.3 TEM pictures of SEDDS/P35 without NDP and with NDP after dispersion in water
(199 folds)………………………………………………………….……….......... 62
4.4 SAXS curves of SEDDS/P35 loaded with NDP, diluted with 1, 4, 6, 10, 40 and 80%
of water and SGF……………………………………………………………….… 66
4.5 Drug dissolution profiles of NDP powder, commercial product, NDP-loaded
SEDDS/P35, NDP-loaded SEDDS/P40………………………………….…... 67
5.1 Zeta potential of solid carriers, SEDDS and solid SEDDS formulations in water and
SGF………………………………………..……………………………………...… 77
5.2 Schematic diagram showing the adsorption of SEDDS composing of oil/surfactant/co
surfactant onto solid carriers and their spontaneous emulsification after exposure
water.………………………………………………………………..…………… 78
5.3 Drug dissolution profiles of SEDDS and solid SEDDS formulations in SGF………… 80
5.4 SEM micrographs of solid carriers and solid SEDDS (1000x)………………………… 84
5.5 Thermograms of NDP, solid carriers and physical mixture of NDP and solid carriers
solid SEDDS……………………………………………………………………… 86
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Figure Page
5.6 Powder X-ray diffractograms of NDP, solid carriers and physical mixture of NDP
and solid carriers and solid SEDDS…………………………………………..…… 86
5.7 Dissolution profiles in SGF of NDP, SEDDS and solid SEDDS formulations using
different solid carriers……………………………………………………………… 89
5.8 Thermograms of NDP, solid carriers and physical mixture of NDP and solid carriers
solid SEDDS, solid SEDDS under accelerated stress condition and long-term
condition study……………….………………………………………………….. 91
5.9 Powder X-ray diffractograms of NDP, solid carriers and physical mixture of NDP
and solid carriers, solid SEDDS under accelerated stress condition and long
-term condition study……………………………..…………………………….. 95
6.1 In vivo plasma profile of commercial product, NDP-loaded SEDDS/P35,
PCS120/P35/50 and NDP-FS200/P35/50 and the NDP powder with fed and
fasted conditions…………………………………..…………………………….. 102
7.1 Properties and structure of various poorly water-soluble drugs used in this study…… 109
7.2 SEM micrographs of PCS120/P35/50 loading with different drugs………………….. 113
7.3 DSC thermograms of drug powders, drug-loaded PCS120/P35 formulations and
physical mixtures of drug and PCS120 (1:5)……………………………………… 114
7.4 Powder X-ray diffractrograms of drug powders, drug-loaded PCS120/P35
formulations and physical mixtures of drug and PCS120 (1:5)…………………… 115
7.5 Drug dissolution profiles of drug powders and SEDDS formulations, and solid
SEDDS formulations loaded with different drugs, in SGF………………………… 117
7.6 Relationship between lipophilicity (LogP) and % drug dissolved at 60 min………… 118
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LIST OF ABBREVIATIONS
%v/v percent volume by volume
%w/v percent weight by volume
%w/w percent weight by weight
oC degree Celsius
Ɵ theta
μL microliter (s)
μg microgram (s)
μm micrometer (s)
Å angstrom (s)
AUC area under the plasma concentration time curve
BCS biopharmaceutical classification system
Cmax maximum concentration
DSC differential scanning calorimetry
FDP felodipine
g gram (s)
h hour (s)
HLB hydrophilic-lipophilic balance
ITZ itraconazole
kV kilovolt (s)
m mater (s)
MDP manidipine hydrochloride
MDT mean dissolution time
mbar millibar (s)
mg milligram (s)
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mL milliliter (s)
NaCMC sodium carboxymethylcellulose
NDP nifedipine
ng nanogram (s)
nm nanometer (s)
PXRD powder X-ray diffractometry
rpm round per minute
SAXS small angle X-ray scattering
SEDDS self-emulsifying drug delivery system
SEM scanning electron microscope
SGF simulated gastric fluid USP without pepsin
SMEDDS self-microemulsifying drug delivery system
SNEDDS self-nanoemulsifying drug delivery system
TEM transmission electron microscope
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CHAPTER 1
Introduction
Oral route is the most convenient and preferred route of drug delivery as it
offers a good patient compliance. However, 40% of drugs delivered via the oral route
have limited therapeutic efficacy due to poor water solubility (1-4). Conventional
techniques, such as salt formation, micronization, solubilization using co-solvents, use
of permeation enhancers, oily solutions and surfactant dispersions that were previously
employed to increase oral bioavailability, revealed limited utility. Although recently
developed strategies, such as new solid dispersion technology and inclusion complexes
using cyclodextrins (5), exhibit good potential, they are successful in some cases and
are specific to drug candidates. The use of self-emulsifying drug delivery system
(SEDDS) is one of the interesting approaches (1, 6). SEDDS is anhydrous form of
nanoemulsion or preconcentrated nanoemulsion. It is isotropic mixture of oil,
surfactant(s) and drug, which spontaneously forms thermodynamically stable oil-in-
water nanoemulsions (usually with globule size less than 200 nm) when introduced into
aqueous phase under gentle agitation conditions (7). SEDDS can also contain co-
emulsifier or co-surfactant and/or solubilizer in order to facilitate nanoemulsification
or improve the drug incorporation. The advantages of SEDDS include possibility of
filling them into unit dosage forms (e.g. soft/hard gelatin capsule), maintaining physical
and/or chemical stability upon long-term storage, improving the bioavailability of
poorly water-soluble drug, and reducing the blood profile variation in the patients
confronted with (gastrointestinal) GI problem (8, 9). However, the SEDDS as liquid
dosage forms has limitations such as, low drug loading capacity, and excipient-capsule
incompatibility (6, 9, 10). To overcome these complications, the liquid SEDDS is
adsorbed on to inert carrier, such as silicon dioxide, to produce solid SEDDS.
In the formulation of a SEDDS, the following points should be considered:
(i) solubility of drug in different oils, surfactants and co-surfactant/co-solvents, and (ii)
selection of oil, surfactant and co-surfactant/co-solvent based on the solubility of drug.
1
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The optimum concentrations of oil, surfactant and co-surfactant/co-solvent necessary
to promote self-emulsification are determined by construction of a ternary phase
diagram.
The main objective of this study is to enhance the drug dissolution and
absorption of poorly water-soluble drug by SEDDS. SEDDS based on HLB value and
ternary phase diagram will be developed. Solid SEDDS containing poorly water-
soluble drug will be prepared by adsorption of above mentioned SEDDS onto solid
carrier. In vitro and in vivo studies will also be performed in order to determine the
efficiency of the system.
For a poorly water-soluble drug, the drug dissolution is the rate-limiting step
during drug absorption process, causing low drug bioavailability. In this study,
nifedipine (NDP), a well-known and most widely used coronary vasodilator, has been
chosen as a model drug. NDP is practically insoluble in water with solubility of 5.8
mg/L in water, pKa <1, LogP of 2.50. The large varieties of liquid or waxy excipients
(ranging from oils through biological lipids, hydrophobic and hydrophilic surfactants,
to water-soluble co-solvents) are available for the formulation of SEDDS. To select
the oil and surfactant in the formulation, the solubility of NDP in various vehicles
including long, medium and short chain triglycerides, fatty acids, surfactants and co-
surfactants will be determined. The vehicle offering high drug solubility will be
selected as an excipient in SEDDS formulation. Different surfactants and their
combinations, depending on HLB value, will be used for preparing SEDDS (Chapter
3). In Chapter 4, a series of self-emulsifying formulations will be prepared by ternary
phase diagram using various concentrations of oil, surfactant and co-surfactant. The
tendency to spontaneously emulsify will be observed. The effect of volume of water
used for diluting SEDDS on spontaneous emulsification will also be determined.
Solid SEDDS will be developed by physical mixing, using various
percentages of three groups of inert solid carriers (Chapter 5). Drug dissolution profiles
of solid SEDDS using different solid carriers will be compared and discussed in terms
of surface area, particle size and porosity of solid carriers. The in vivo absorption of
selected formulation that have good dissolution profile will be examined using male
Wistar rats to confirm efficiency of the solid SEDDS (Chapter 6).
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The other poorly water-soluble drugs have been applied in selected SEDDS
formulations. The effect of drugs with different lipophilicity (LogP), that is, nifedipine
(NDP), felodipine (FDP), manidipine (MDP), and itraconazole (ITZ) on morphology,
physicochemical properties and dissolution profiles of solid SEDDS has been also
determined (Chapter 7).
In Chapter 8, a summary and general conclusion of these study is provided
and some suggestions for future work are also provided.
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CHAPTER 2
Literature review
2.1 Poorly water-soluble drugs
2.2 Self-emulsifying drug delivery system (SEDDS)
2.3 Excipients for SEDDS
2.3.1.1 Oils
2.3.1.2 Surfactants
2.3.1.3 Co-solvents
2.3.1.4 Additives
2.3.1.5 Excipient compatibility
2.4 Mechanism of self-emulsification
2.5 Formulation of SEDDS
2.5.1 Liquid SEDDS
2.5.1.1 HLB calculation
2.5.1.2 Ternary phase diagram
2.5.2 Techniques for solid SEDDS preparation
2.5.2.1 Extrusion-spheronization
2.5.2.2 Melt granulation
2.5.2.3 Spray drying
2.5.2.4 Adsorption on solid carrier
2.6 Evaluation of SEDDS
2.6.1 Size of emulsion and robustness of dilution
2.6.2 Small angle X-ray scattering (SAXS)
2.6.3 Solid state characterization
2.6.4 In vitro evaluation of SEDDS
2.6.5 Drug absorption by SEDDS and in vivo test
4
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2.1 Poorly water-soluble drugs
The oral route is the most preferred route of drug delivery for treatment of
a number of diseases. All new chemical entities have been estimated that anywhere
from 40 to as much as 70 percent entering drug development process possess inadequate
water solubility to allow invariable GI absorption of a magnitude sufficiency to ensure
therapeutic efficacy (11). The new chemical entities are poorly water-soluble drug,
which leads to poor oral bioavailability, high variable absorption and lack of dose
proportionality. The absorption rate of poorly water-soluble drug from the GI lumen is
governed by dissolution step (1-4). Several formulation approaches have been
developed to overcome such problems arising out of low solubility and bioavailability,
which may result in improved therapeutic efficacy of these drugs. Various application
techniques have been developed for improving the dissolution profile of drugs with low
solubility, such as the use of surfactant, lipid permeation enhancer, micronization, salt
formation, complex formation with cyclodextrins, nanoparticles, solid dispersion, co-
grinding and emulsification (5).
The poor and variable absorption provided these compounds by
conventional formulations can be complicated by a significantly and potentially
positive food effect. Drugs in the GI tract are exposed to a medium of partially digested
food, consisting of protein, carbohydrate, and fat. The benefits of food or oil on
hydrophobic drug were revealed and lipid-based drug delivery systems have shown
great potentials in delivery of lipophilic drugs, with several successfully marketed
products. The effect of medium composition on the intrinsic dissolution rate of
itraconazole is evaluated as this extremely poor solubility and its bioavailability were
reported (12, 13). The influence of liquid intake and a lipid-rich meal on the
bioavailability of a lipophilic drug (danazol) was investigated in a randomized four-
way crossover study by Sunesen et al. (14) Intake of danazol with a lipid-rich meal
increased the bioavailability by 400%.
The bioavailability of poorly water-soluble drugs is poor due to slow and/or
incomplete drug dissolution in the lumen of the GI tract. In this problem, increased
drug absorption can be achieved by the use of delivery systems, which can improve the
rate and/or the extent of drug solubility into aqueous intestinal fluids. For a lipophilic
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drug compound, the principle aim is to achieve a formulation while the poorly water-
soluble drug is dissolving in the liquid vehicle or solvent. Once present in the GI tract,
the liquid vehicle is diluted by the surrounding endogenous fluid. While this dilution
step, the lipophilic drug remains in solution, and forms a liquid dispersion.
2.2 Self-emulsifying drug delivery system (SEDDS)
The beneficial effects of food or oil on hydrophobic drug were reported and
several successful oral pharmaceutical products have been marketed as lipid-based
formulation. Subsequently, there is substantial interest in the potential of lipid-based
formulation (15). The absorption kinetics of lipid in small intestine is always formed
small droplets by endogenous substances (bile salts). The fatty acids and triglycerides
containing poorly water-soluble substances, for example, drugs and oil-soluble
vitamins in GI tract are absorbed into the epithelial intestine (11). Lipid-based delivery
system is a mixture of oil, surfactant, co-surfactant and co-solvent. The mixtures are
usually self-dispersing system, often referred to as SEDDS. Self-emulsifying oil
system, the ability of oil to accommodate a lipophilic drug in solution can be improved
by the addition of surface active agents. The surfactant also performs the functional
dispersion of the bulk liquid vehicle encountered dilution in GI media. Hence, the drug
is dissolved in fine droplets of the oil/surfactant mixtures which spread immediately in
the GI tract. The lipid-based formulation has been divided into 4 types by Pouton et al.
(16). Table 2.1 indicates the lipid formulation classification system and the
fundamental differences between Type I, II, III and IV formulations and properties
including advantages and disadvantages of each type. The simple bulk oil solution
(Type I) can be formed an emulsion with a required endogenous substance (bile salt) in
GI. SEDDS has been developed with considering needless endogenous emulsifiers.
Co-solvent is contained in Type III and IV. The precipitated drug can be occurred after
dilution at few minutes. The example of a poorly water-soluble drug dissolved in a
pure co-solvent is considered such as polyethylene glycol or propylene glycol. When
the formulation is diluted with water, the solvent capacity of the mixture approximately
decreases logarithmically as the formulation is diluted. The result is drug precipitation.
However, the micellar solubilized system as surface active agent properties would be
lost solubilization ability gradually (4).
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Table 2.1 Lipid formulation classification system: characteristic features, advantages
and disadvantages of the four essential types of lipid-based formulations. (16)
Formulation type
Material Characteristic Advantage Disadvantage
Type I Oil without surfactants (e.g. tri-, di-and monoglycerides)
Non-dispersing, requires digestion
GRAS status; simple; excellent capsule compatibility
There will be a poor solvent capacity in formulation unless drug is highly lipophilic
Type II Oil and water-insoluble surfactants
SEDDS formed without water-soluble components
Unlikely to lose solvent capacity on dispersion
Turbid o/w dispersion (particle size 0.25–2 μm)
Type III Oil, surfactants, co-solvents (both water-insoluble and water-soluble excipients)
SEDDS/SMEDDS formed with water-soluble components
Clear or almost clear dispersion; drug absorption without digestion
Possible loss of solvent capacity on dispersion; less easily digested
Type IV Water-soluble surfactants and co-solvents (no oil)
Formulation disperses typically to form a micellar solution
There is a good solvent in formulation for many drugs.
Likely loss of solvent capacity on dispersion; may not be digestible
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Figure 2.1 The advantage of SEDDS in oral drug absorption.
Enhanced drug absorption
Emulsion
Enhanced drug permeation
Enhanced drug dissolution
Greater chemical/ enzymatic stability
Reduced drug efflux
SEDDS
Enhanced lymphatic transport
Reduced hepatic metabolism
Reduced gastrointestinal metabolism
Greater interfacial area for absorption
Enhancement on oral drug absorption
8
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The enhanced oral drug absorption of SEDDS can be described in Figure
2.1 (7). After the SEDDS is placed in stomach, the emulsion is formed immediately,
as providing a large interfacial area for absorption. In this process, drug is dissolved in
oil droplets. The drug is protected from the enzymes and pH degradation by dissolving
in oil droplets. SEDDS reduces hepatic first pass effect and then decreases drug
metabolism. Surfactant is used to disperse the emulsion. Drug efflux of cells can be
reduced by some surfactants as a specific substrate of P-glycoprotein for instant
polyoxyls (Cremophor®) (17-22). Thus, the SEDDS is a good potential to enhance drug
absorption, reduce metabolism and elimination of drug.
2.3 Excipients for SEDDS
A wide range of triglycerides, partial glycerides, semi-synthetic oily esters,
and semi-synthetic/non-ionic surfactant esters are available from excipient suppliers.
The toxicity of high concentration of surfactant is concerned. Water-insoluble
surfactant enters and fluidizes cell membranes and water-soluble surfactant have the
potential to solubilize the bilayer of membrane. Surfactants may irritate the cell as a
result of these non-specific effects. There is a significant document on the interaction
of surfactant with biological membrane. In general, non-ionic surfactant is less toxic
than cationic surfactant and anionic surfactant (16, 23). SEDDS typically contains non-
ionic surfactant. Typically, bulky surfactant, such as polysorbates or polyethoxylated
vegetable oil, is less toxic than single-chain surfactant, and esters are less toxic than
ethers (which are non-digestible) (23). Non-ionic surfactant in lipid-based formulation
is usually considered to be satisfactory for oral administration, and the several marketed
products has agreed to produce the lipid-based products. LD50 values of non-ionic
surfactant for oral and intravenous are more than 50 g/kg and 5 g/kg, respectively (24),
so the formulation contained 1 g of surfactant is acceptable for uses in acute oral drug
administration. The popular groups of surfactant, the sorbitan esters and their
ethoxylated derivatives (polysorbates), are commonly used.
In history, excipients were considered to be inert ingredients that would be
used primarily as diluents, fillers, binders, lubricants, coatings, solvents, and dyes, in
the production of drug products. In some cases, known and/or unknown interactions
can occur between an excipient and drug, other inactives, or container in close system.
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Consequently, not all excipients are inert substances, and some may be irritating
potential. In the United States, the Food and Drug Administration (U.S. FDA) has
reported lists generally recognized as safe (GRAS) substances (25, 26). A year ago, the
agency also maintains a list of Inactive Ingredient Guide (IIG) for excipients that have
been permitted and included in the product. This guide provides the consideration of
excipients with the maximum concentration by specific route of administration or
dosage form for each excipient. Both GRAS listings and IIG information can be used
in pharmaceutical products. The another document, the U.S. FDA has recently issued
a guidance for industry to control the nonclinical studies for the safety evaluation of
new pharmaceutical inactive compounds (27). This guidance not only repoets the
toxicity of new excipient, but also describes the safety estimates for excipients offered
for use in over-the-counter and generic drug products. The information also presents
testing strategies for pharmaceuticals proposal for short-term, intermediate, and long-
term intake.
2.3.1 Oils
They are commonly ingested in food, fully digested and absorbed.
Vegetable oil is glyceride esters of mixed unsaturated long-chain fatty acids, typically
known as long-chain triglycerides (LCT) (28). Oil from different vegetable bases have
different quantities of each fatty acid. The fatty acid components of coconut and palm
kernel oil are noteworthy in that they are unusually rich in saturated medium-chain oil
(C8, C10 and particularly C12) (29). The generic product from distilled coconut oil is
medium-chain triglycerides (MCT) (known as glyceryl tricaprylate/caprate) which is
available from several dealers and usually contains glyceryl esters with predominantly
saturated C8 (50–80%) and C10 (20–45%) fatty acids. Triglycerides are highly
lipophilic properties and their solvent capability for drugs is a function of the effective
concentration of the ester moieties, thus on a ratio of MCT usually has higher solvent
capacity than LCT. In addition, MCT is not subject to oxidation, so MCT is a popular
choice for use in lipid-based drug delivery system (2). The low solvent capacity of
short chain triglycerides (SCT) was reported by Macgregor et al. (30) The precipitation
of progesterone is observed at the bottom of vessel for in vitro lipolysis study.
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In addition, the in vivo results in rats are agreed with in vitro study. Similar observations
are found for griseofulvin and penclomedine (31).
Table 2.2 and Table 2.3 list the vegetable oils, animal fats and oils of natural
origin in pharmacopoeia, used most commonly for manufacturing of lipid-based drug
delivery system.
Table 2.2 Vegetable oil in pharmacopoeia. (32)
Name/Source Ph.Eur. USP/NF JP
Almond oil/Prunus dulcis + (R, V) - -
Arachis oil (Peanut oil)/Arachis hypogea + (R, H) - +
Camellia oil/Camellia japonica - - +
Castor oil/Ricinus communis + (V, H) + +
Coconut oil/Cocos nucifera + (R) - +
Cottonseed oil/Gossypium hirsutum + (H) + -
Maize oil (Corn oil)/Zeya mais + (R) + +
Olive oil/Olea europaea + (R, V) + +
Rapeseed oil/Brassica napus, B. campestris + (R) + +
Safflower oil/Carthamus tinctorius - + -
Sesame oil/Sesamum indicum + (R) + +
Soyabeen oil/Glycine soja,G. max + (R, H) - +
Sunflower oil/Helianthus annuus + (R) - -
Triglycerides, media chain/Cocos nucifera, Elaeis
guineensis
+ + -
Wheat germ oil/Triticum aestivi + (R, V) - -
R – Refined oil; V – Virgin oil; H – Hydrogenated oil
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Table 2.3 Animal fats and oil in pharmacopoeia (32)
Name/Source Ph.Eur. USP/NF JP
Beef tallow (Sevum bovinum)/Bos taurus var.
Domesticus - - +
Hard fat (Adeps solidus)/Sus scrofa; Semisyntehetic
from natural fatty acid
+ - -
Lard (Adeps suillus)/Sus scrofa - - +
Cod-liver oil (Iecoris aselli oleum)/Gadus morhua;
Gadidae
+type A, B - +
Fish oil (Piscis maritimi oleum)/Engualidae,
Carangidae, Clupeidae, Osmeridae, Scrombroidae,
Ammodytidae
+ - +
Omega-3-acid triglycerides (Omega-3 acidorum
trigycerida)/Engaulidae, Carangidae, Clupeidae,
Osmeridae, Salmonidae, Scrombroidae
+ - -
Shark liver oil/Somniosus microcephalus, Lamna
nasus
- + -
2.3.2 Surfactants
The most generally used surfactants for formulation of SEDDS are water-
soluble, though by definition these materials can only be utilized in Type III or Type
IV formulations (Table 2.1). Above their critical micelle concentration, these materials
dissolve in pure water at low concentrations to form micellar solutions. This implies
an hydrophilic-lipophilic balance (HLB) value of nearly 12 or greater (11, 16). The
fatty acid components can be either unsaturated or saturated. The popular castor oil
derivative, polyoxyl 40 hydrogenated castor oil (P40), is a typical example of a product
with saturated alkyl chains, resulting from hydrogenation of materials, which are from
a vegetable oil (33). Its close relative, polyoxyl 35 castor oil (P35), which has also been
used commonly, has a slightly lower degree of ethoxylation but is not hydrogenated
and is therefore unsaturated (34). Many materials are produced by reacting
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polyethylene glycol (PEG) with hydrolyzed vegetable oil. This results in fatty acid
mono and di-esters of PEG combined with partial glycerides and some free form
(unreacted) PEG (35, 36). Castor oil ethoxylates synthesized using ethylene oxide are
distinguished by the buildup of polyoxyethylene chains coupled to the hydroxyl group
at the C12 position of ricinoleic acid. Castor oil is 87% ricinoleate so castor oil
ethoxylates are unique surfactant with an uncommon chemical structure conformation
(37). The importance of this chemistry to formulation has not been sufficiently
explored, although it should be remembered that polyoxyls (Cremophor®) are very
heterogeneous materials, which makes it difficult to study the influence of chemical
structure on physical, biological or toxicological properties. The enhancement of oral
bioavailability is directly affect by surfactant on drug efflux of transport proteins,
typified by P-glycoprotein (38, 39). Polyoxyls have been occupied as inhibitors of
efflux pumps, but the mechanism of inhibition has not been determined. This could be
a non-specific conformational transformation caused by the penetration of surfactant
molecules into the plasma membrane, the adsorption of surfactants to the outer surface
of the efflux pump, or even the interaction of small molecules with the intracellular
domains of the efflux pump (18, 39). Co-surfactant was used in the formulation of
emulsion and microemulsion to reduce the concentration of surfactant and decrease the
interfacial tension for the emulsion formation (40). Furthermore, the co-surfactant may
also increase drug solubility in the formulation. Example of lipophilic co-surfactant
that may be used in the formulation of SEDDS includes non-ionic surfactant, such as
propylene glycol, diethylene glycol monoethyl ether (DGE), oleoyl macrogol-6
glycerides, polyglyceryl-3 oleate and glyceryl triacetate (41-43). In the study of Yoo
et al. (44), the model drug lutein was successfully formulated as SEDDS for immediate
self-emulsification and dissolution by using mixture of glycerol monooleates as oil,
caprylocaproyl macrogol-8 glycerides as surfactant, and diethylene glycol monoethyl
ether or polyethylene glycol as co-surfactant. Almost complete dissolution was
achieved after 15 min. It has been seen that co-surfactant was required in the
formulation of SEDDS.
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2.3.3 Co-solvents
Several marketed lipid-based products contain water-soluble co-solvents
(16). The most popular materials are PEG 400, propylene glycol, ethanol and glycerol,
though other approved co-solvents have been used in experimental studies. There are
at least three reasons why co-solvents have been involved in SEDDS. Ethanol was used
in early cyclosporin products at a low concentration to aid the dissolution of the drug
during manufacture. More commonly, it has been assumed that co-solvents could be
incorporated into raise the solvent capacity of the formulation for drugs, which dissolve
easily in co-solvents. However, to enhance the solvent capacity, the co-solvent must
be present at high concentration and this is related to the risk of drug precipitation when
the formulation is dispersed in water. Co-solvents lose their solvent capacity rapidly
following dilution. For many drugs, the association between co-solvent concentration
and solubility is close to logarithmic curve. Another reason for the inclusion of co-
solvents is to aid the dispersion of systems, which contain a high proportion of water-
soluble surfactant. There are applied limits on the concentrations of co-solvents, which
can be used, governed by the issues of immiscibility with oil components and also the
potential incompatibilities of low molecular weight co-solvents with capsule shells (9).
2.3.4 Additives
Lipid-soluble antioxidants, i.e., α-tocopherol, β-carotene, butylated
hydroxytoluene (BHT), butylated hydroxyanisole (BHA) or propyl gallate could
potentially be contained in lipid mixture formulations to avoid either unsaturated fatty
acid chains or drugs from the oxidation (11, 16, 45).
2.3.5 Excipient compatibility
A thorough and methodical evaluation of the numerous chemical
incompatibilities that could exist between lipid excipients and drug substances have not
been published (11). However, it is well-recognized that a number of lipid and some
surfactant excipients are vulnerable to oxidation, with the attendant formation of
highly-reactive peroxide species. Peroxide creation can be detrimental not only to
stabilize a formulated drug substance, but also have been shown to cause gelatin cross-
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linking, resulting in the delayed disintegration of the capsule shell which in turn, may
adversely affect drug release (9). Lipid oxidation can be controlled by limiting the use
of unsaturated lipids, by the inclusion of suitable antioxidants, or through the use of
wrapped hard gelatin capsule shells, which are relatively impermeable to oxygen.
2.4 Mechanism of self-emulsification
The mechanism of self-emulsification is not yet completely understood (1).
Nevertheless, it could been described in term of thermodynamics that self-
emulsification takes place while the entropy change preferring dispersion is better than
the energy required to rise the surface area of the dispersion state. The free energy of
a conventional emulsion formulation is a direct function of the energy required to
generate a new surface between the oil and water phases. The two phases of the
emulsion tend to isolate with time to reduce the interfacial area and the free energy of
the systems. The conventional emulsifying agents stabilize emulsions, resulting from
aqueous dilution, by forming a monolayer around the emulsion droplets, reducing the
interfacial energy and forming an obstacle to coalescence. On the other hand,
emulsification occurs spontaneously with SEDDS because the free energy required to
form the emulsion is low (either positive or negative) (46, 47). The emulsification was
recommended to be related to water penetration into the several liquid crystal (LC) or
gel phases formed on the surface of the droplet (48). The interface between the oil and
aqueous continuous phases is formed upon addition of a binary mixture (oil/non-ionic
surfactant) to water. This is followed by the solubilization of water within the oil phase
as a result of aqueous penetration through the interface (49). Aqueous penetration will
lead to the formation of the dispersed LC phase, following mild agitation of the self-
emulsifying system, water will quickly penetrate into the aqueous cores and lead to
interface interruption and droplet formation. Detailed studies have been carried out to
determine the association of the LC phase in the emulsion formation process (49). Also,
particle size analysis and low frequency dielectric spectroscopy were utilized to
examine the self-emulsifying properties of a series of CCG (a mixture of mono- and
diglycerides of capric and caprylic acids)/polysorbates 80 systems. The results advised
that there might be a complex relationship between LC formation and emulsion
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formation. Moreover, the occurrence of the drug compound may alter the emulsion
characteristics, probably by interacting with the LC phase.
2.5 Formulation of SEDDS
The poorly water-soluble drug can often be dissolved in SEDDS allowing
them to be formulated as unit dosage forms for oral administration. When a formulation
is released into gut lumen. The SEDDS formulation should instantaneously form a
dispersion, which should remain stable on dilution. The hydrophobic drug remains
solubilized until the time that is relevant to its absorption in gut. The following issues
should be considered; (i) solubility of drug in different oils, surfactants and co-
surfactant/co-solvents, and (ii) selection of oil, surfactant and co-surfactant/co-solvent
based on the solubility of drug. The optimum concentrations of oil, surfactant and co-
surfactant/co-solvent necessary to promote self-emulsification are determined by
construction of a ternary phase diagram. HLB value of the surfactant is key factor for
the formation of (nano)emulsion (50). Wang et al. (51) purposed an alternative method
to prepare SEDDS containing a mixture of surfactants with similar structure (i.e.,
polysorbates and sorbitan monoester) by HLB Although, the design of experiment
(DOE) can be used for a tool of formulation, DOE is grouped in ternary phase diagram
because DOE is used ratios of 3 components as same as the ternary phase diagram.
DOE of a phase diagram is a time-consuming process, requiring careful synthesis and
characterization of all phases in a system. The example of SEDDS studies prepared by
HLB calculation technique or ternary phase diagram is shown in Table 2.4.
2.5.1 Liquid SEDDS
2.5.1.1 HLB calculation
The selection of emulsifiers based on their structural features over the HLB
has also been a subject of discussion by Liu et al. (51) and Wang et al. (50, 51). Wang
et al. (52) explained that emulsifier molecular structure has a significant effect on the
final emulsion droplet size. This study suggested that a droplet size is a crucial factor
for the efficiency and of SEDDS application. Several pairs of emulsifiers with similar
structure at the optimum HLB value of corresponding oil phase were attracted.
Ibuprofen was combined into the SEDDS to increase its dissolution profile. Four series
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of emulsions, comprising of four different types of oil (methyl decanoate, isopropyl
myristate, methyl oleate and ethyl oleate), were examined to find the required HLB to
obtain a nanoemulsion with the smallest droplet size. They demonstrated that
appropriate surfactant and the specific ratio of combination can be used to formulate
SEDDS. It has been described that the smallest droplet size is achieved when the HLB
of surfactant are matched with oil. Nanoemulsions with the smallest droplet size are
achieved with the mixtures of polysorbates 80 and sorbitan monolaurate, and the largest
droplet sizes are obtained by using a polysorbates 20 and sorbitan monolaurate mixture.
The required HLB of methyl decanoate was 11.7 at the required HLB of other three oils
is 11.3. Nanoemulsions with droplet diameter as low as 17 nm are achieved in the
system composting of isopropyl myristate. These results suggest an important effect of
the optimized HLB values on the nanoemulsion preparation. It is widely known that
hydrophilic and lipophilic surfactant can form mixed films at the water/oil interface.
The surfactant molecules which have equal hydrocarbon chain length and have no
double bond in the side chain, would arrange more densely at the interface. The
constituents or structures of interfacial films have been considered as important factors
for the formation of nanoemulsions.
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Table 2.4 Example of SEDDS studies, prepared by HLB calculation technique or
ternary phase diagram.
Research topic Methods of formulation
Authors
- Formation and stability of paraffin oil-in-
water nano-emulsions prepared by the
emulsion inversion point method
HLB
calculation
Liu et al., 2006 (50)
- Design and optimization of a new self-
nanoemulsifying drug delivery system
Wang et al., 2009 (51)
- Studies on the formation of O/W nano-
emulsions, by low-energy emulsification
methods, suitable for pharmaceutical
applications
Ternary
phase
diagram
Sadurní et al., 2005
(52)
- A new self-emulsifying drug delivery
system (SEDDS) for poorly soluble drugs:
Characterization, dissolution, in vitro
digestion and incorporation into solid
pellets
Abdalla et al. 2008 (53)
- Self-nanoemulsifying granules of
ezetimibe: Design, optimization and
evaluation
Dixit et al., 2008 (54)
- Enhanced oral bioavailability of
dexibuprofen by a novel solid self-
emulsifying drug delivery system
(SEDDS)
Balakrishnan et al.,
2009 (55)
- Formulation development and
bioavailability evaluation of a self-
nanoemulsified drug delivery system of
oleanolic acid
Xi et al., 2009 (56)
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Table 2.4 (continued)
Research topic Methods of
formulation
Authors
- Self-nanoemulsifying drug delivery
system (SNEDDS) for oral delivery of
Zedoary essential oil: formulation and
bioavailability studies
Ternary
phase
diagram
Zhao et al., 2010 (57)
- Self-double-emulsifying drug delivery
system (SEDDS): A new way for oral
delivery of drugs with high solubility and
low permeability
Qi et al., 2011(58)
- Study of cosurfactant effect on
nanoemulsifying area and development of
lercanidipine loaded (SNEDDS) self
nanoemulsifying drug delivery system
Parmar et al., 2011 (59)
- Preparation, characterization, and in vivo
evaluation of a self-nanoemulsifying drug
delivery system (SNEDDS) loaded with
morin-phospholipid complex.
Zhang et al., 2011 (60)
- Self-nanoemulsifying drug delivery
system of persimmon leaf extract:
Optimization and bioavailability studies
Li et al., 2011 (61)
- Polymeric nanocapsules with SEDDS
oil-core for the controlled and enhanced
oral absorption of cyclosporine
Park et al., 2013 (62)
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2.5.1.2 Ternary phase diagram
The ternary phase diagrams are always used to form SEDDS, thus all
combinations of surfactant and oil can be compared easily to select the surfactant and
oil mixture. The studies of equilibrium phase behavior have been used to describe the
mechanisms of dispersion of SEDDS (8, 63, 64). The conventional approach is to
weigh out mixtures into test tubes, mix the components and store the tubes in a water
bath until they have equilibrated. Phase behaviors of the combination (oil, surfactant
and water) systems are mapped out using a phase diagram. If more than two excipients
are used in the formulation, it is sensible to combine groups of miscible excipients into
two groups so that the influence of aqueous dilution of anhydrous formulations can be
observed for a variety of formulations. This strategy was used to identify the existence
of lamellar and cubic phases formed (65). Zhao et al. (57) generated pseudo-ternary
phase diagrams containing a series of ratio of surfactant and oil with fixed drug
(zedoary turmeric oil) concentration at 30% w/w. The mixture is gently mixed with
100 mL of distilled water in a glass beaker at ambient condition. The tendency to
disperse spontaneously and the progress of emulsion form is visually observed. If a
clear and slightly bluish or a slightly less clear microemulsion is rapidly formed (within
1 min), the corresponding area will be plotted in the ternary phase diagram, the SEDDS
region is identified. The selected formulation from this study, comprising of zedoary
turmeric oil, ethyl oleate, polysorbates 80, DGE (30.8:7.7:40.5:21, w/w) and drug is
developed. After dilution with water, the selected formulation is rapidly formed the
emulsion droplets with a mean size of 68.3±1.6 nm and zeta potential of −41.2±1.3 mV.
The active components remain stable in the optimized SEDDS kept at 25oC for more
than a year. Following the oral administration of zedoary turmeric oil-SEDDS in rats,
both AUC and Cmax of germacrone, a representative bioactive indicator of zedoary
turmeric oil, increase by 1.7 folds and 2.5 folds, respectively, compared with the
unformulated zedoary turmeric oil. This study has clearly revealed the potential utility
of SEDDS for formulating zedoary turmeric oil with improved dissolution, stability and
oral bioavailability.
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2.5.2 Techniques for solid SEDDS preparation
Generally, the formulations are prepared from a single bulk solution that can
be filled and sealed in hard or soft gelatin capsules. The industrial processes used for
the liquid-filled hard or soft capsules are extensively slower production and higher cost
than conventional tablets and capsules. This disadvantage is solved by solid self-
emulsifying drug delivery systems (solid SEDDS), which will transform liquid or semi-
solid formulations into solid particles (powders, granules or pellets). This could
subsequently be filled into capsules, sachets or compressed into tablets (33). The
technique to achieve solid SEDDS can be developed from liquid SEDDS including
extrusion/extrusion spheronization (66-69), melt granulation (70), spray drying (55, 71)
and adsorption on solid carriers (33, 72-76).
2.5.2.1 Extrusion-spheronization
Solid SEDDS prepared by extrusion-spheronization or pelletization method
comprises of several steps such as the wet granulation of liquid/semisolid self-
emulsifying formulation with the solid carriers, the extrusion of wet mass, the
spheronization of extrudates, drying of the spheroids of pellet (67, 77). The main
advantages of extrusion-spheronization are scale-up, high yield, low particle size
distribution, good flow particles and low friability of pellets. Numerous steps involved
in this method are considered as main disadvantage because it results in increased time,
cost and higher risk of contamination due to the numerous parts of equipment (66). A
pellet formulation of nitrendipine-loaded solid SEDDS is prepared by
extrusion/spheronization technique from liquid SEDDS (nitrendipine, caprylic/capric
triglyceride, P40, polysorbate 80 and DGE), adsorbents (silicon dioxide and
crospovidone), microcrystalline cellulose and lactose (66). SEDDS pellets containing
30% of liquid, exhibited uniform size about 1000 μm and round shape, droplet size
distribution of emulsion after dispersion are nearly similar to the liquid SEDDS.
Furthermore, the in vitro release profiles of liquid SEDDS and SEDDS pellet
formulations are same and significantly higher than the conventional tablet. The in vivo
evaluations have been tested in fasted beagle dogs. The AUC of nitrendipine form solid
SEDDS is also same when comparing with the liquid SEDDS but higher than the
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conventional tablet. The adsorbent can be used to physically adsorb before fabricating
pellet and the manufacturing process. However, the retarding effect should be
considered. Extrusion can be achieved by melting the material by heating before forcing
it through the die in a process called hot melt extrusion. In order to be processed by hot-
melt extrusion, the materials should be meltable and thermally stable (66, 78) . The
advantages of hot-melt extrusion are continuous process (few unit operations, solvent
free as well as anhydrous process) high drug loading and generation of amorphous
form.
2.5.2.2 Melt granulation
In melt granulation, the granulating fluid is the molten material with other
components of formulation and will create agglomerated powder, resulting in solidified
mass upon cooling. Melt granulation process is required a high-shear mixer equipped
with an electric heated jacket. This process is not suitable for heat sensitive active
ingredient. Simple production, solvent free and high drug loading capacity are the
advantages of melt granulation (70). The use of propranolol oleate as a melt granulation
binder phase was developed by Crowley et al. (70). A range of propranolol oleate binder
concentration has been investigated, using the uniformity of binder distribution and the
granule friability as tests for optimizing binder concentration. The results showed that
the dissolution of drug is increased by melt granulation (70).
2.5.2.3 Spray-drying
Spray-drying technique involves the preparation of drug, lipid, surfactant
and solid carrier solution or suspension in a suitable solvent (e.g., water or ethanol). It
is then atomized to create liquid droplets, which are dried by the evaporation of solvent
in the chamber to produce a solid SEDDS (71, 79-85). The solid SEDDS is then
harvested into the collecting chamber. The main benefit provides a fine particle finished
product that is easy for tableting and filling into capsules. The solid inert carriers used
to produce such kind of formulations may be hydrophobic (e.g., colloidal silica) (55).
The dry emulsions solve the issues of drug stability and avoid the use of organic
solvents which may be toxic. Process complication and high cost are the disadvantages
of spray-drying. The aerosol, temperature, air flow pattern and drying chamber design
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affect the properties of final spray-dried product. Spray-drying of liquid SEDDS with
colloidal silicon dioxide to improve the oral bioavailability of dexibuprofen was
performed by Balakrishnan et al. (55). The liquid SEDDS composed of dexibuprofen,
caprylocaproyl macrogol-8 glycerides, propylene glycol caprylate, and oleoyl
macrogol-6 glycerides are added with suspended colloidal silicon dioxide in ethanol.
The mixture is spray-dried with mini spray-dryer. The result showed that the
dissolution of solid SEDDS of dexibuprofen is improved, when compared with
dexibuprofen powder. The initial plasma levels of dexibuprofen in solid SEDDS are
significantly higher than that raw material dexibuprofen powder. AUC and Cmax of
solid SEDDS are higher than that of dexibuprofen powder.
2.5.2.4 Adsorption on solid carrier
The liquid SEDDS can alternatively mixed with adsorbent carrier in order
to formulate the solid SEDDS. The adsorption process is simple and involves the
addition of the liquid formulation onto the carrier of choice by mixing in a blender (74).
The solid carrier can be calcium silicate, magnesium aluminometasilicate, silicon
dioxide, carbon nanotubes and lactose, etc. The selected solid carrier should adsorb
large quantity of liquid SEDDS and the resulting powder should be free-flowing. This
method also yields the product with good content uniformity. However, reduced drug
load is main disadvantage. The resulting free-flowing powder may then be filled
directly into capsules or alternatively mixed with suitable excipients before
compression into tablets. The adsorption technique has been successfully applied to
gentamicin and erythropoietin as solid SEDDS formulations that maintained their
bioavailability enhancing effect after adsorption on carriers (74, 86, 87). The
dissolution and dynamics of powder flow upon griseofluvin of solid SEDDS in addition
to silica and theirs derivatives were determined by Agarwal et al. (72). Silica
derivatives have been used as adsorbents to load liquid SEDDS with mortar and pestle.
Drug dissolution form adsorbed-SEDDS is found to depend on pore size and the drug
nucleation at the lipid/adsorbent interface. Moreover, the increased dissolution rate is
observed with an increase in adsorbent surface area and is independent on the chemical
nature of adsorbents. So, to manufacture free-flowing powder comprising of liquid
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SEDDS, special attention should be considered, especially particle size specific area of
adsorbent in solid SEDDS.
2.6 Evaluation of SEDDS
2.6.1 Size of emulsion and robustness of dilution
The size of emulsion has an influence on oral drug absorption, hence,
determination of droplet emulsion size after dilution is required to determine, for
instance, atomic force microscopy (AFM), transmission electron microscopy (TEM),
scanning electron microscope (SEM) and static laser light scattering (SLS). The
assessment of the dispersion rate and the resultant emulsion diameters of SEDDS are
desirable. Little attention has been given to determine dispersion rate since the first
attempts are available (64). The dispersion rate could not been precisely determined.
Commonly well-formulated SEDDS is rapidly dispersed within seconds under the
conditions of mild agitation, and the visual observation to decide good and poor
formulations may be passable. An experienced formulator can also attain a good
indication of emulsion size and polydispersity by eye observation but, with the
availability of modern Fraunhofer diffraction sizers and photon correlation
spectrometers, the effect of formulation on particle size can be easily inspected. Poor
SEDDS are technically challenging to size because typically they are coarse,
polydisperse, and sensitive to dilution and agitation. Poor formulation are removed
from study. Poor formulation can be divided from an acceptable formulation by
determining polydispersity and size of emulsion. Tarr and Yalkowsky (88)
demonstrated in a gut perfusion experiment that emulsion droplet size affects the rate
absorption of cyclosporin A. The intestinal absorption of cyclosporine was examined
in situ in rats containing an olive oil emulsion prepared by either stirring or
homogenization process. The emulsion size of the homogenized emulsion is 2-time
lower than that of the stirred emulsion. The apparent permeability of cyclosporine A
from the homogenized emulsion is about twice that of the emulsion prepared by stirring.
These results demonstrate that the bioavailability of cyclosporine A administered in an
emulsion can possibly be increased by improving its rate of absorption through the
reduction of droplet size.
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Robustness of dilution is very important for SEDDS formulation to ensure
that the emulsion formed have similar properties at different dilutions to achieve
uniform drug release behavior and that the drug may precipitate at higher dilution in GI
tract, which may delay the absorption of the drug from the SEDDS [7]. Different fold
dilutions of selected formulations were exposed to different media to mimic the in vivo
conditions where the formulation would encounter gradual dilution [8]. Robustness to
dilution of SEDDS was investigated by Balakumar et al. (89). The formulation was
subjected to 50, 100 and 1000-time dilution in water, pH 1.2, pH 3 and pH 6.6. The
resulting emulsions are found to be in the acceptable nano-size (<200 nm), proving their
robustness to dilution. The results ensure the prospect of uniform drug release profile
in vivo.
2.6.2 Small angle X-ray scattering (SAXS)
The process of self-emulsification proceeds through formation of liquid
crystals (LC) and gel phases. Dissolution of drug from SNEDDS is highly dependent
on LC formed at the interface, since it is likely to affect the angle of curvature of the
droplet formed and the resistance offered for partitioning of drug into aqueous media.
SAXS technique has been to record the elastic scattering of X-ray by from an
inhomogeneous sample at very low angle (typically 0.1-1.0°). This information contain
shape and size of macromolecules, the distance of partially ordered structure and pore
size (15). Self-emulsification process was investigated by Maestro et al. (90). The
results form SAXS indicated that nanoemulsion is formed through a dilution of cubic
LC as ordered structure. The study of Sadurní et al. (52) shows the similar results. The
spectra of the sample composed with water and surfactant (35:65) are discovered the
ordered structure of hexagonal and lamellar LC.
2.6.3 Solid state characterization
In case of solid SEDDS, the physical state of drug in solid SEDDS can be
characterized by powder X-ray diffractometry (PXRD) and differential scanning
calorimetry (DSC) since it would have an important influence on in vitro drug
dissolution characteristics. DSC is most widely used for thermal analysis to monitor
endothermic process (melting, solid-solid phase transition and chemical degradation)
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as well as exothermic process (crystallization and decomposition). Characterization of
physical states can be useful in the study since it can indicate the existence of possible
drug-excipient interaction in the formulation.
Thermal characterization of solid SEDDS containing dexibuprofen was
investigated by Balakrishnan et al. (55). No obvious peak of drug is found in solid
SEDDS, indicating that the drug may be present in molecularly dissolved state in the
formulation. From powder X-ray diffractogram of solid SEDDS, No peak presenting
crystal of dexibuprofen is found. In vitro dissolution test showed that solid SEDDS has
a faster in vitro release rate than the drug powder (55). In another study, the cryogenic
grinding of solid SEDDS has been developed by Chambin et al. (91) In the thermogram
of solid SEDDS, interaction peak of Gelucire® 44/14 and ketoprofen is found. The
large endotherm of new peak is observed indicating that interaction is due to the
solubilization of ketoprofen into a fraction of molten Gelucire® 44/14.
2.6.4 In vitro dissolution of SEDDS
In recent years, several successful oral products have been marketed as lipid
systems, remarkably cyclosporin A (originally marketed as Sandimmune® E and now
as the developed product Neoral® E) and the two HIV protease inhibitors, ritonavir and
saquinavir. The advantageous effects of food or oil on hydrophobic drug have been
reported and several successful oral pharmaceutical products have been sold as lipid-
based formulation. The reasons underlying the lack of application of these technologies
are not entirely clear yet, but likely reflect the edge understanding of the formulation
parameters that are responsible for good in vivo performance and the detail that
relatively few in vivo studies in humans have been studied and reported in the literature
when being compared with conventional dosage forms (92). Perhaps most
significantly, at least from a developmental position, the absence of effective in vitro
tests that are extrapolative of in vivo correlation has significantly hindered the
successful development of SEDDS. In the context of oral solid dosage forms, it has
generally been recognized that there are multiple roles for in vitro dissolution testing.
For example, it is engaged to guide the drug development and the selection of
appropriate formulations for further in vivo studies. It is also used as a preliminary test
for the detection of possible bioequivalence between products before and after changes
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in manufacturing and/or formulation. As a quality control tool, in vitro dissolution can
be used to set specifications for batch release and ensure batch-to-batch uniformity.
With appropriate methods, in vitro dissolution can be further correlated with in vivo
performance and employed as a surrogate for bioequivalence studies. Additionally, the
USP II dissolution testing can be employed. The conventional in vitro dissolution
methods, however, may not be appropriate for predicting in vivo performance of
SEDDS since the dissolution of the drug and GI processing of the lipid vehicle
(including digestion and dispersion) are intrinsically linked to each other. Ideally, the
in vitro release testing should incorporate the dynamics of lipid digestion, the formation
of various intermediate colloidal products, and the solubilization of the drug under the
study. To date, considerable researches have been undertaken in an attempt to develop
appropriate in vitro models that mimic the dispersion and digestion phenomena
observed in vivo for SEDDS. The improvement of SEDDS products has been slow,
which is probably due, in part, to the perceived problems of physical and chemical
instability, as well as unpredictable bioavailability and in vivo performance of these
preparation (93, 94). The lack of predictability for product quality and performance
may be attributed to the empirical and iterative processes conventionally used for the
design of these products.
2.6.5 Drug absorption by SEDDS and in vivo test
The appropriately designed in vivo studies of formulations, generally
performed in the early phase of drug development, can provide important information
about the impact of the excipients on the overall bioavailability and the
pharmacokinetic profile of drug. Rats and dogs are the most frequently utilized animal
species for estimating the performance of oral SEDDS. During initial development,
rats are generally suitable for studies. The preparation is delivered by a syringeable
liquid which can be administered via oral gavage and provided that the study does not
require the administration of a human-sized dosage form. Some investigators have
questioned the use of the rat for evaluating oral SEDDS performance due to a species-
specific difference in bile secretion. Bile flow from gallbladder is deficient in rat (95-
97). By comparison, bile flow in the dog is more similar to man, suggesting that this
species may be more relevant for projecting the clinical performance of oral SEDDS.
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On the other hands, other investigators have suggested that the rat (96), in comparison
to the dog (98), is a more proper model for predicting drug absorption in man, which
would rationally be probable to influence the relevance of these species with regarding
to projecting drug absorption from SEDDS. The choice of animal species for
preclinical evaluation of a SEDDS is probably best anticipated by the stage of drug
development and the specific questions that the formulator wishes to address. Due to
lower cost and greater ease of management, small animals (e.g., rats) typically represent
the best choice for most initial stage of investigations, while a larger animal, such as a
dog, is most appropriately utilized for the final stages of testing which require the
evaluation of a prototype dosage form intended for administration to humans.
The lymphatic system in the body consists of a network of lymphatic vessels
and lymph nodes, which permit the absorption of interstitial fluid holding
macromolecules (proteins) and particulate cellular matter (97). The route of the access
to the lymphatic system has been utilized for targeting therapeutic agents to regional
lymph nodes after local parenteral administration (99). This can be exemplified by the
use of colloidal systems such as emulsion and liposomes for subcutaneous injection.
Some highly lipophilic drugs, oral administration, have also been shown to the achieved
access to the systemic circulation via intestinal lymphatic transport, avoiding the
hepatic first-pass metabolism and providing a higher drug bioavailability. However,
Hauss (99) described that while the principal physiological purpose of the intestinal
lymphatic system is to digest food lipid from the gut, lymphatic transport can be
responsible for a portion of the total absorb of oil-soluble vitamins and lipophilic drugs,
as well (11). These drugs are transported to the systemic circulation in association with
chylomicrons and very low-density lipoproteins (99-103) and by-pass the liver as well
as any potentially hepatic first-pass metabolism, which offers a further dramatically
increased bioavailability. The process by which lipophilic drugs associate with
chylomicrons is not clearly understood, but it appears to be governed, at least in part,
by relative drug hydrophobicity (e.g., octanol:water LogP) and solubility in
triglyceride, which constitutes 95% of the chylomicron bulk (11, 104, 105). The drug
targeted for lymphatic system has been investigated by Muranishi (106). Ontazolast is
extensive hepatic first pass metabolism drug and it has solubility in soybean oil of 55
mg/ml, and a LogP of 4. The formulations of ontazolast investigated include a
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suspension, a 20% soybean o/w emulsion, two SEDDS containing Gelucire® 44/14 and
glycerol monooleates in the ratios 50:50 and 80:20, respectively, and a solution of the
drug in glycerol monooleates alone. All the lipid formulations increase the
bioavailability of ontazolast, while the SEDDS provides more rapid absorption. The
emulsions prolong lymphatic transport and this may be related to triglyceride vehicle
as association with slow gastric emptying time. The glycerol monooleates solution
provides the highest rate of lymphatic triglyceride transport, thus resulting in
improvement the partition of drug into the lymph. The SEDDS formulations result in
the highest concentration of ontazolast in the chylomicron triglyceride. The authors
suggested that SEDDS provides rapid absorption of ontazolast, produced higher
concentrations of the drug in the enterocyte and improves lymphatic drug transport by
a concentration partitioning phenomenon (106).
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CHAPTER 3
Formulation of SEDDS based on HLB value
3.1 Introduction
3.2 Materials and methods
3.2.1 Materials
3.2.2 Determination of drug solubility in various vehicles
3.2.3 Preparation of mixed surfactant system
3.2.4 Preparation of SEDDS formulations
3.2.4.1 Preparation of liquid SEDDS
3.2.4.2 Preparation of solid SEDDS
3.2.5 Characterization of SEDDS
3.2.5.1 Visual observation of self-emulsification
3.2.5.2 Droplet size analysis
3.2.5.3 Morphology examination of solid SEDDS
3.2.5.4 Solid state characterization of solid SEDDS
3.2.6 In vitro dissolution study
3.2.7 Statistical analysis
3.3 Results and discussion
3.3.1 Solubility of NDP in various vehicles
3.3.2 Preparation and characterization of SEDDS
3.3.3 Preparation and characterization of solid SEDDS
3.3.4 In vitro dissolution test
3.4 Conclusion
30
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3.1 Introduction
The HLB of surfactant offers essential information on its potential use in
formulation of SEDDS. The SEDDS formulation with high HLB surfactant can form
oil-in-water nanoemulsions immediately and rapidly spread in aqueous medium. It
would keep drug solubilized for a prolonged period of time at absorption site for
effective absorption and prevent drug precipitation within GI lumen (15). More than
one surfactant may be blended together to achieve the desired HLB. Mixture of
different surfactant types often exhibit synergism in their effects in the properties of a
system. This synergism can be attributed to non-ideal mixing effects in the aggregates,
resulting in critical micellization concentration and interfacial tension that are
substantially lower than would be expected on the basis of the properties of the unmixed
surfactants (107). In addition to an appropriate HLB value, the constitution and
molecular structure of mixed surfactants on the water/oil interface is also an important
factor affecting the formation of nanoemulsions after dispersion in a medium.
Recently, Wang et al. (51) reported that different pairs of surfactants with similar
structure (i.e., ethoxylated sorbitan monoester and sorbitan monoester) at the optimum
HLB value provide different droplet sizes depending on molecular structure of
surfactant. To date, there are a limited number of published reports available in the
literature that have prepared the SEDDS by using mixed surfactants of polysorbates,
based on HLB of the mixture (51, 108). The pharmaceutical nanoemulsions are often
composed of other surfactants with different structures, for example, polyoxyls, which
has not been reported in the literatures. Therefore, it is interesting to investigate the
effect of the HLB of different blends of surfactants.
In this chapter, the SEDDS and solid SEDDS containing NDP was
developed based on the HLB of mixed surfactants. To select the oil and surfactant in
the formulation, the solubility of NDP in various vehicles including oil and surfactant
was determined. Different surfactants and their combinations, depending on HLB
value, were used for preparing SEDDS. Solid SEDDS was prepared by mixing the
SEDDS with inert solid carriers. The SEDDS and solid SEDDS were then
characterized for their size after dispersion, morphology, physicochemical properties
and drug dissolution behavior.
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3.2 Materials and methods
3.2.1 Materials
NDP (lot number 20091217) was purchased from Xilin Pharmaceutical Raw Material
Co., Ltd. (Jiangsu, China). As NDP was light sensitive, all samples were kept in an
amber-colored container or wrapped in aluminum foil during whole experimental
process. Olive oil (lot number 4023275325), castor oil (lot number 315362532),
sunflower oil (lot number 2007082023), almond oil (lot number 2153272653), apricot
oil (lot number 51260512202) and coconut oil (lot number 2053254242) were
purchased form P.C. Drug Center (Thailand). Caprylic/capric triglycerides (Miglyol®
812 (lot number080708)) and Miglyol® 810 (lot number 070706)) and caprylic/capric
glyceride (Imwitor® 742 (Lot Number 090809), referred as CCG) were purchased form
Sasol (Hamburg, Germany). Miglyol® 812 and Miglyol® 810 differ only in C8/C10
ratio. Miglyol® 810 has lower C10 content than Miglyol® 812. Hexanoic acid (lot
number 54396PH), octanoic acid (lot number 1463420), decanoic acid (lot number
BCBB4747), oleic acid (lot number 60298PJ459) and richinoleic acid (lot number
1433410) were purchased form Sigma-Aldrich (Missouri, USA). Polyoxyethylene 20
sorbitan monolaurate or polysorbate 20 (Tween® 20, HLB 16.7, lot number G190074),
polyoxyethylene 20 sorbitanmonooleate or polysorbate 80 (Tween® 80, HLB 15.0, lot
number 24174), sorbitan monolaurate (Span® 20, HLB 8.6, lot number SCA04) and
sorbitan monooleate (Span® 80, HLB 4.3, lot number 2011413) were purchased form
P.C. Drug Center (Bangkok, Thailand). Polyoxyl 40 hydrogenated castor oil
(Cremophor® RH40 referred to as P40, HLB 14-16, lot number 04770897V0) and
polyoxyl 35 castor oil (Cremophor® EL referred to as P35, HLB 12-14, lot number
29000716K0) were a gift form BASF (Thai) Co., Ltd. (Bangkok, Thailand). The
chemical structure of investigated surfactants is shown in Figure 3.1. Fumed silica;
hydrophilic grade (Aerosil® 200 referred to as FS200, lot number3152082016) and
hydrophobic grade (Aerosil® R972 referred to as FSR, lot number 7631869) were
supplied by Evonik Industries (Hanua, Germany). Other chemicals were of reagent or
analytical grade and used without further purification. Distilled water was used in all
preparations. The simulated gastric fluid USP without pepsin (SGF) was prepared by
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dissolving 2 g of sodium chloride and 7 mL of hydrochloric acid into distilled water
and adjusting volume to 1000 mL, pH to 1.2, and used as test medium.
Figure 3.1 Chemical structure of oil and surfactants investigated in this study.
Cremophor® EL (P35)
Cremophor® RH40 (P40)
Imwitor® 742 (CCG)
Span® 80 (Sorbitan monooleate)
Tween® 80 (Polysorbate 80)
Tween® 20 (Polysorbate 20) Span® 20 (Sorbitan monolaurate)
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3.2.2 Determination of drug solubility in various vehicles
Solubility of NDP was determined in various vehicles by adding excess
amount of NDP (500 mg) in 1 mL of a pure vehicle in glass tubes. The drug suspension
was equilibrated at 25 C in a thermostatically controlled bath for 72 h. After
equilibration, the tubes were centrifuged at 3,500 rpm for 15 min and the clear
supernatants were analyzed for NDP with a high performance liquid chromatography
(HPLC, model JASCO PU-2089plus quaternary gradient inert pump, and a JASCO
UV-2070plus multiwavelength UV–vis detector, Jasco, Japan) using Luna 5u C18
column (5 μm, 4.6 nm 25 cm) (Phenomenex, USA). The mobile phase composing
of water, acetonitrile and methanol (50:25:25) was filtered through a 0.22-μm
membrane filter, and degassed in a sonicator bath before use. The flow rate of mobile
phase was 1 mL/min, and the UV detection wavelength was 235 nm.
3.2.3 Preparation of mixed surfactant system
A frequently used method for selection of surfactants is known as the HLB
method. The hydrophilic surfactant (polysorbate 20, polysorbate 80, P40 or P35) was
mixed with hydrophobic surfactant (sorbitan monolaurate or sorbitan monooleate).
There were 8 binary mixed surfactant systems obtained as followed:
polysorbate 20/sorbitan monolaurate, polysorbate 20/sorbitan monooleate, polysorbate
80/sorbitan monolaurate, polysorbate 80/sorbitan monooleate, P40/sorbitan
monolaurate, P40/sorbitan monooleate, P35/sorbitan monolaurate, and P35/sorbitan
monooleate. The HLB number of each mixed surfactant system (HLBmix) was
calculated by the following equation:
HLBmix = fA HLBA + fB HLBB (1)
where HLBA, HLBB are HLB values, and fA, fB are the weight fractions of surfactant A
and surfactant B, respectively. The HLBmix required in this study ranged from 8 to 15
(109). The surfactant mixing ratio calculated from the above-mentioned equation was
defined as the weight percent of corresponding surfactants, as shown in Table 3.1.
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Table 3.1 Ratio of mixed surfactants used in the formulations prepared at various HLB values.
HLB Surfactant mixing ratio (weight percent) Polysorbate20/ Sorbitan monolaurate
Polysorbate20/ Sorbitan monooleate
Polysorbate80/ Sorbitan monolaurate
Polysorbate80/ Sorbitan monooleate
P35/ Sorbitan monolaurate
P35/ Sorbitan monooleate
P40/ Sorbitan monolaurate
P40/ Sorbitan monooleate
8.0 n/a 29.8/70.2 n/a 34.6/65.4 n/a 42.5/57.5 n/a 34.6/65.4 8.5 n/a 33.9/66.1 n/a 39.3/60.7 n/a 48.3/51.7 n/a 39.3/60.9 8.6 0/100 34.7/65.3 0/100 40.2/59.8 0/100 49.4/50.6 0/100 40.2/59.8 9.0 4.9/95.1 37.9/62.1 6.3/93.2 43.9/56.1 9.1/90.9 54.0/46.0 6.3/93.7 43.9/56.1 9.5 11.2/88.9 41.9/58.1 14.1/85.9 48.6/51.4 20.5/79.5 59.8/40.2 14.1/85.9 48.6/51.4 10.0 17.3/82.7 46.0/54.0 21.9/78.1 53.3/46.7 31.8/68.2 65.5/34.5 21.9/78.1 53.3/46.7 10.5 23.5/76.5 50.0/50.0 29.7/70.3 57.9/42.1 43.2/56.8 71.3/28.7 29.7/70.3 57.9/42.1 11.0 29.6/70.4 54.0/46.0 37.5/62.5 62.6/37.4 54.5/45.5 77.0/23.0 37.5/62.5 62.5/37.4 11.5 35.8/64.2 58.1/41.9 45.3/54.7 67.3/32.7 65.9/34.1 82.8/17.2 45.3/54.7 67.3/32.7 12.0 42.0/58.0 62.1/37.9 53.1/46.9 72.0/28.0 77.3/22.7 88.5/11.5 53.1/46.9 72.0/28.0 12.5 48.1/51.9 66.1/33.9 60.9/39.1 76.6/23.4 88.6/11.4 94.3/5.7 60.9/39.1 76.6/23.4 13.0 54.3/45.7 70.2/29.8 68.8/31.3 81.3/18.7 100/0 100/0 68.8/31.2 81.3/18.7 13.5 60.5/39.5 74.2/25.8 76.6/23.4 86.0/14.0 n/a n/a 76.6/23.4 86.0/14.0 14.0 66.7/33.3 78.2/21.8 84.4/15.6 90.7/9.3 n/a n/a 84.4/15.6 90.7/9.3 14.5 72.8/27.2 82.3/17.7 92.2/7.8 95.3/4.7 n/a n/a 92.2/7.8 95.3/4.7 15.0 79.0/21.0 86.3/13.7 100/0 100/0 n/a n/a 100/0 100/0
Note: n/a = not applicable
35
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3.2.4 Preparation of SEDDS formulations
3.2.4.1 Preparation of liquid SEDDS
The formulations were prepared by mixing oil (CCG) with mixed surfactant
systems at a ratio of 1:1. The formulations were stored at ambient temperature (25ºC)
until further use. Selected formulations those corresponded to HLBmix of 10 were
loaded with NDP at the concentration of 30 mg/mL. Drug-loaded formulations were
stored in the amber glass container, at 25ºC, for 3 days in order to observe immediate
stability. Unstable formulations (e.g., precipitation of drug crystals and/or phase
separation) were excluded from the study.
3.2.4.2 Preparation of solid SEDDS
Selected SEDDS formulations were simply adsorbed onto two types of
silicon dioxide, i.e., FS200 (hydrophilic grade) and FSR (hydrophobic grade) by
trituration using 20, 30, 40, 50% (w/w) silicon dioxide in formulation (Table 3.2).
3.2.5 Characterization of SEDDS
3.2.5.1 Visual observation of self-emulsification
Evaluation of the self-emulsifying properties of SEDDS were visually
observed. The formulations were diluted with gentle mixing in distilled water at a
dilution ratio of 1:100. The mixtures were gently folded and stored at ambient
temperature (25ºC) for 2 h before further characterization. The emulsion formation
(i.e., until a clear homogenous system was obtained) was observed visually.
3.2.5.2 Droplet size analysis
The droplet size of emulsion formed after reconstitution was determined by static
laser light scattering (model LA-950, Horiba, Japan). SEDDS was diluted with
distilled water at a dilution ratio of 1:100. Solid SEDDS was centrifuged at 2000 rpm
for 10 minutes to remove the solid carriers. All measurements were repeated 3 times
and the values of mean diameter were reported.
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Table 3.2 Composition SEDDS and solid SEDDS formulation
Formulation P40 (%)
Sorbitan monooleate (%)
CCG (%) Solid carriers (%)
Solid carriers type
Liquid SEDDS 55.3 46.7 50.0 - -
A20 21.3 18.7 40.0 20.0 FS200
A30 18.7 16.3 35.0 30.0 FS200
A40 16.0 14.0 30.0 40.0 FS200
A50 13.3 11.7 25.0 50.0 FS200
R20 21.3 18.7 40.0 20.0 FSR
R30 18.7 16.3 35.0 30.0 FSR
R40 16.0 14.0 30.0 40.0 FSR
R50 13.3 11.7 25.0 50.0 FSR
3.2.5.3 Morphology examination of solid SEDDS
The external structure of the solid SEDDS was investigated by a scanning
electron microscope (SEM; model Maxim-2000, CamScan Analytical, England) with
an accelerating voltage of 15 keV. The samples were fixed on a stub using double-
sided adhesive tape and coated in a vacuum with thin gold layer before investigation.
3.2.5.4 Solid state characterization of solid SEDDS
3.2.5.4.1 Differential scanning calorimetry (DSC)
Thermal analysis of NDP, solid SEDDS and the physical mixture of NDP
and solid carrier was performed by differential scanning calorimeter (model Sapphire,
Perkin Elmer, USA). An accurate amount of samples (abount 2.5 mg) was placed inside
standard crimped aluminum pan and heated from 25 to 200°C at a heating rate of
10°C/minute.
3.2.5.4.2 Powder X-ray diffractometry (PXRD)
PXRD patterns of NDP in various solid SEDDS formulations were carried
out with powder X-ray diffractometer (model MiniFlex II, Rigaku, Japan), at 30 kV, 15
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mA and angle speed of 4o/min over the range of 5°-45° 2θ using Cu Kα radiation
wavelength of 1.5406 Å.
3.2.6 In vitro dissolution study
The dissolution test was carried out using a USP dissolution apparatus II
(model PWS3C, Pharma Test, Germany) with 900 mL of simulated gastric fluid USP
without pepsin (SGF, pH 1.2) as a dissolution medium at 37±0.5oC. The paddle speed
was adjusted to 50 rpm. NDP powder, liquid SEDDS and solid SEDDS (equivalent to
10 mg of NDP) that filled in hard capsules was put into a sinker before placing in a
dissolution vessel, which was protected from light. At predetermined time intervals
(i.e., 5, 10, 15, 30, 60, 90, and 120 min), 5-mL aliquots of the medium were collected,
filtered through 0.45-μm nylon membrane filters to remove the agglomerated silicon
dioxide and analyzed for the NDP concentration by HPLC analysis as mentioned above.
The same volume (5 mL) of fresh medium was added to compensate for the loss due to
sampling. The dissolution experiments were carried out in triplicate.
3.2.7 Statistical analysis
Analysis of variance (ANOVA) and Levene’s test for homogeneity of
variance were carried out using SPSS version 10.0 for Windows (SPSS Inc., USA).
Post hoc testing (p<0.05) of the multiple comparisons was performed by either the
Scheffé or Games-Howell test depending on whether Levene’s test was insignificant or
significant, respectively.
3.3 Results and discussion
3.3.1 Solubility of NDP in various vehicles
In the formulation of SEDDS, the selection of suitable oil, surfactant and
co-surfactant plays an important role to enhance the solubility of drug and drug loading.
The components in SEDDS formulation should be selected to have maximum drug
solubility along with good miscibility with each other to produce a stable formulation
(55). The solubility of NDP in various vehicles was presented in Table 3.3. Higher
solubility of NDP in the oil phase was important criterion, as it would help the
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Table 3.3 Solubility of nifedipine in various vehicles (n=3)
Vehicle Solubility of nifedipine (μg/mL)
Oils
Almond oils 1,322.6±207.4
Apricot oils 1,209.6±22.3
Caster oils 7,656.5±2,003.2
Coconut oils 1,869.6±206.3
Imwitor® 742 11,828.4±1,655.3
Miglyol® 810 4,027.0±258.2
Miglyol® 812 3,867.8±152.0
Olive oils 1,244.9±208.8
Sunflower oils 1,511.7±174.9
Fatty acids
Decanoic acid 1,590.5±166.3
Hexanoic acid 4,020.3±247.0
Octanoic acid 2,579.3±199.8
Oleic acid 452.8±66.8
Ricinoleic acid 3,271.5±309.4
Surfactants
Cremorphor® EL (HLB 12-14) 61,270.3±6,150.7
Cremorphor® RH40 (HLB 14-16) 67,214.5±9,823.5
Span® 20 (HLB 8.6) 3,073.3±69.2
Span® 80 (HLB 4.3) 2,822.1±535.1
Tween® 20 (HLB 16.7) 76,066.3±22,768.9
Tween® 80 (HLB 15) 66,988.4±2,479.5
Solvents
Acetonitrile 8,461.4±433.2
Ethanol 25,038.4±6,540.4
Isopropanol 20,458.0±6,596.8
Water 5.8±0.1
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nanoemulsion to maintain the drug in solubilized form. Among the oils and fatty acids
tested in this study, CCG (caprylic/capric glyceride), which is amphiphilic compound
with surface active property, showed the highest solubility of NDP and was then
selected as an oil component. CCG can promote water penetration, self dispersibility
of lipid formulations and had good solvent capacity for NDP. Some hydroxyl groups
within the glycerol ester of CCG are free, contributing to its polarity and excellent
solvent properties for many drugs. NDP solubility in fatty acids was comparable to the
vegetable oils and fatty acid esters (Miglyol®) but much lower than CCG.
Various hydrophilic non-ionic surfactants with a relatively high HLB, such
as the polysorbates (Tween®) and polyoxyls (Cremophor®) have been widely used due
to their relatively low toxicity (11). The results shown in Table 3.3 suggest that NDP
was highly soluble in polysorbates and polyoxyls. Polysorbate 20 (HLB 16.7) was
found to have the maximum solubilizing capacity while sorbitan monooleate (HLB 4.3)
demonstrated the minimum solubilizing capacity for NDP. It could be seen that the
solubility of NDP was depended on the HLB of surfactant, that is, the higher the HLB,
the higher the solubility of NDP. The solubility of NDP in some organic solvents has
also been tested as shown in Table 3.3. This information can be used for selecting
suitable system for HPLC analysis.
3.3.2 Preparation and characterization of SEDDS
A surfactant dissolved in liquid can either adsorb at the interface or self-
assemble to form micelles, resulting from the hydrophobic effect. The lyophobic group
of the surfactant tends to be expulsed from the liquid in which the surfactant is
dissolved. The adsorption of surfactants at the interface induces a structural change of
the interfacial area, and in many cases, a decrease of the interfacial tension. It seems
obvious that, by changing the surfactant, the interfacial tension decreases to a different
degree which affects the final droplet size (110). The HLB method has been
demonstrated to be a useful tool in selecting the optimal type of surfactants for a certain
oil phase (108). SEDDS was prepared with 50% (w/w) oil phase and 50% (w/w) mixed
surfactants at HLB values ranging from 8 to 15. Eight series of mixed surfactants,
consisting of four different types of hydrophilic surfactant (i.e., polysorbate 20,
polysorbate 80, P40, P35) and two types of lipophilic surfactant (i.e., sorbitan
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monolaurate, sorbitan monooleate), were examined to determine the suitable HLB to
obtain SEDDS. Blends of surfactants at various ratios were used to prepare mixed
surfactants with a range of HLB values (Table 3.1). The effect of HLB of different
mixed surfactants on the droplet size of emulsions obtained after dispersion in aqueous
medium is shown in Figures 3.2 and 3.3. The results suggested that even though the
HLB values were the same, there is a wide difference in the emulsion droplet size. It
is obvious that the droplet size depended primarily on surfactant molecular structure.
Nanoemulsions could be formed from mixtures of polyoxyls and sorbitan monoester at
suitable HLB (Figure 3.2). It could be seen that the droplet size decreased when the
HLB of mixed surfactants (polyoxyls/sorbitan monoester) was higher than 9 for those
using sorbitan monooleate and 11.5 for those using sorbitan monolaurate. At HLB 10,
for example, mixtures of polyoxyls (polyethoxylated castor oil which is a blend of
ricinoleic acid, polyglycol ester, glyerol polyglycol esters, and polyglycols) and
lipophilic surfactant with longer CH chain length (C18, sorbitan monooleate) produced
the nano-sized emulsion while those with shorter CH chain length (C12, sorbitan
monolaurate) provided only micron-sized emulsion. From Figure 3.2, it is observed
that the increase in HLB exhibited a declined trend, that is, the emulsion droplet size
decreased with a higher HLB. According to HLB calculation, higher values indicated
surfactants owned higher hydrophilicity which facilitated reducing curvature of
interface for the oil that owned relatively high solubility, leading to smaller droplet size
(111). This is the possible reason for the decreasing trend in emulsion droplet size.
In contrast, nano-sized emulsions could not be obtained in the system
containing polysorbate and sorbitan monoester (Figure 3.3). In any combination of
polysorbate and sorbitan monoester, the emulsion droplet size was not significant
different (about 10 m). The correlation between HLB and mean droplet size
demonstrates the nearly linear line rather than the sigmoid curve reported previously
(51). This is probably attributable to the absence of co-surfactant in our experiments.
In their formulations, however, the co-surfactant (i.e., 1, 2-octanediol) is added in the
formulations containing mixtures of polysorbate 80 and sorbitan monolaurate. The
addition of 1,2-octanediol decreases the surfactant content necessary to produce
nanoemulsions and significantly affects the droplet size (51).
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Figure 3.2 Droplet size of emulsions containing CCG and polyoxyls/sorbitan
monoester system (ratio of 1:1) as a function of HLB
(b)
(a)
10
100
1000
10000
100000
7 8 9 10 11 12 13 14 15HLB
Size
(nm
)
10
100
1000
10000
100000
7 8 9 10 11 12 13 14 15HLB
Size
(nm
)P40/sorbitan monolaurate
P40/sorbitan monooleate
P35/sorbitan monolaurate
P35/sorbitan monooleate
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(a)
Figure 3.3 Droplet size of emulsions containing CCG and polysorbate/sorbitan
monoester system (ratio of 1:1) as a function of HLB
(b)
10
100
1000
10000
100000
7 8 9 10 11 12 13 14 15HLB
Size
(nm
)
10
100
1000
10000
100000
7 8 9 10 11 12 13 14 15
Size
(nm
)
HLB
polysorbate 80/sorbitan monolaurate polysorbate 80/sorbitan monooleate
polysorbate 20/sorbitan monolaurate
polysorbate 20/sorbitan monooleate
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Without the co-surfactant, it is difficult to reduce the effective HLB to a value within
the range required for nanoemulsion formation.
Figure 3.4 shows the schematic representation of the configuration into oil-
in-water (nano)emulsion. The results were in agreement with Dai et al. (112) who
reported that molecular structure of surfactant has a significant effect on the final
emulsion droplet size. However, the change of hydrophilic surfactant (P35 and P40) in
the mixed surfactants, when the lipophilic surfactant remained unchanged, did not
influence the emulsion droplet size. This means that the structure of polyoxyls has a
greater effect on the droplet size than that of sorbitan monoester. These results
suggested that the difference in CH chain length between polyoxyls and sorbitan
monoester assisted the formation of nanoemulsions. However, at HLB = 12-13,
nanoemulsions can be produced from all polyoxyls and sorbitan monoester blends. It
seems that a branch alkyl structure of both P35 and P40 had an effect on the penetration
of oil onto the curved film interface, thus resulting in the self-formation of
nanoemulsion (113). Molecular modeling and docking studies of P35 and γ-tocotrienol
were reported by Alayoubi et al. (114). The low energy docked structures clearly
suggested that γ-tocotrienol binds to P35 deep inside the hydrophobic pocket. For P35,
it was observed that most of the low energy structures are formed when the isoprenyl
group of γ-tocotrienol is docked near the hydrophobic acyl chains, forming a hydrogen
bond with the hydroxyl group of P35. In this study, the molecule of sorbitan monoester,
which is structurally similar to γ-tocotrienol, may be docked in the hydrophobic pocket
size in P35. Chemically, sorbitan monooleate featuring unsaturated fatty acid side
chains may repulse the hydrophobic chain in P35, attributing to smaller droplet size of
emulsion than Sorbitan monolaurate (saturated fatty acid) as presented in Figure 3.4.
From the results obtained, the SEDDS formulation containing a mixture of
P40 and sorbitan monooleate at a ratio corresponded to HLB 10 was selected for
loading a poorly water-soluble drug, NDP (about 30 mg/mL). The NDP-loaded
SEDDS was incubated at 25°C for 3 days. A yellow and clear solution was apparently
observed without drug precipitation and phase separation. The SEDDS formulation
was diluted (100 folds) with distilled water and then kept for 2 h before droplet size
measurement. Droplet size of both blank and NDP-loaded SEDDS after diluting in
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aqueous medium was found to be similar (about 73-74 nm), as shown in Table 3.3.
This confirmed the self-nanoemulsifying nature of SEDDS.
Figure 3.4 Schematic representation of the micellar configuration into oil-in-water
(nano) emulsion containing (a) polyoxyls/sorbitan monooleate, (b) polyoxyls/sorbitan
monolaurate, and (c) polysorbate/sorbitan monooleate.
Table 3.4 Droplet size of SEDDS using a mixed surfactant of
P40/sorbitan monooleate, prepared at HLB 10, after dispersion in water (n=3).
Formulation Size (nm) ± S.D.
Blank SEDDS 73.1±1.0
NDP-loaded SEDDS 74.0±0.8
NDP-loaded solid SEDDS 75.0±2.0
Polyoxyls
Sorbitan monolaurate
Sorbitan monooleate
Polysorbate
H bond interaction
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3.3.3 Preparation and characterization of solid SEDDS
The selected NDP-loaded SEDDS formulation (using CCG and mixed
surfactant of P40 and sorbitan monooleate, at HLB value of 10) was adsorbed on to
fumed silica (amorphous anhydrous colloidal silicon dioxide), i.e., FS200 or FSR.
When the amount of hydrophilic adsorbent, FS200, in the formulation was 20%, a
paste-like, semisolid mass was obtained after incorporating liquid SEDDS to the
adsorbent. However, free-flowing powders were obtained when the amount of FS200
was 30% or more, according to its large surface area (200 m2/g). Jannin et al. (33)
stated that up to 70% w/w of SEDDS is possible to be adsorbed on to suitable solid
carriers. By using hydrophobic adsorbent, FSR (surface area of 110 m2/g), liquid
SEDDS was readily transformed to highly viscous oleogels regardless of the amount of
adsorbent (i.e., 20-50% in the formulation). Figure 3.5 demonstrates SEM images of
FS200, FSR and solid SEDDS containing 40% of FS200 or FSR. Both FS200 and FSR
appeared with a rough surface with porous particles (Figures 3.5a, b). However, the
solid SEDDS appeared as smooth surface particles agglomerated to form larger
particles (Figures 3.5c, d). This indicated that the liquid SEDDS is adsorbed or coated
on the surface of fumed silica. Moreover, the solid SEDDS containing FSR showed
smoother surface than that containing FS200, resulting from its appearance as gel. No
distinct crystal was evident on the surface of the particles after adsorbing the liquid
SEDDS on the surface of fumed silica. The solid state properties of NDP in the solid
SEDDS were investigated since it would have an important influence on the in vitro
dissolution and in vivo release characteristics.
DSC curves of NDP, physical mixture of NDP and FS, SEDDS and solid
SEDDS formulations containing a mixture of P40 and sorbitan monooleate are shown
in Figure 3.6. Pure NDP showed a sharp endothermic peak at about 174 C. FS200 and
FSR did not show any peak over the whole range of the temperature tested. The
physical mixture showed a small endothermic peak for NDP. No representative peak of
NDP was observed for solid SEDDS formulations, indicating that the drug was present
in molecularly dissolved state in solid SEDDS (115).
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(a)
(d) (c)
(b)
Figure 3.5 SEM images of (a) FS200, (b) FSR, (c) solid SEDDS containing 40%
FS200, and (d) solid SEDDS containing 40% FSR.
The PXRD patterns of NDP, physical mixture of NDP and FS, SEDDS and
solid SEDDS formulations containing a mixture of P40 and sorbitan monooleate are
shown in Figure 3.7. NDP raw material is crystalline as demonstrated by sharp and high
intensity peaks. Both fumed silicon dioxide powders are amorphous having no
crystalline structure. The same characteristic peaks of NDP but with low intensity were
observed in the physical mixture of NDP and fumed silica. All the SEDDS and solid
SEDDS formulations did not show the characteristic peaks of NDP. These findings
suggest that the NDP crystals were molecularly dispersed in the SEDDS.
10 μm
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Figure 3.6 DSC thermograms of NDP, physical mixture, SEDDS and solid SEDDS
formulations containing P40 and sorbitan monooleate. Note: NDP = nifedipine;
PMFS200 = physical mixture of NDP and FS200; PMFSR = physical mixture of NDP
and FSR; A20 = solid SEDDS containing 20% FS200; A50 = solid SEDDS containing
50% FS200; R20 = solid SEDDS containing 20% FSR; R50 = solid SEDDS containing
50% FSR.
Temperature (oC)
FS200
R20 R50
A20
PMFS200
NDP
A50
PMFSR
FSR
20 40 60 80 100 120 140 160 180 200
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Figure 3.7 Powder X-ray diffractograms of NDP, physical mixture, SEDDS and solid
SEDDS formulations containing P40 and Sorbitan monooleate. Note: NDP =
nifedipine; PMFS200 = physical mixture of NDP and FS200; PMFSR = physical
mixture of NDP and FSR; A20 = solid SEDDS containing 20% FS200; A50 = solid
SEDDS containing 50% FS200; R20 = solid SEDDS containing 20% FSR; R50 = solid
SEDDS containing 50% FSR.
5 10 15 20 25 30 35 40 45
2θ (degree)
FS200
R20
R50
A20
PMFSR
PMFS200
NDP
A50
FSR
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3.3.4 In vitro dissolution test
In vitro dissolution experiments were conducted to evaluate the effect of
different types and amounts of adsorbent on the dissolution of NDP from the solid
SEDDS formulations. Figure 3.8 shows the percentage of NDP dissolved from
different formulations in SGF. The dissolution of NDP powder in SGF was incomplete,
i.e., about 10% of NDP dissolved, and precipitation of NDP was observed. In the self-
emulsifying system, a mixture of oil, surfactant and drug forms oil-in-water emulsions
when introduced into an aqueous phase. It is suggested that the oil/surfactant and water
phases effectively swell, decrease the oil droplet size and eventually increase the
dissolution rate. As seen in Figure 3.8, the dissolution of NDP from SEDDS and solid
SEDDS was significantly improved, compared with the NDP powder, and no
precipitation was noticed until the end of the experiment. This might be due to the
increased effective surface area and alteration in the native crystalline form of the drug,
as discussed above.
The liquid SEDDS formulation gave dissolution of about 90% within 10
min, after the dissolution of hard gelatin capsule, as a result of fast self-emulsion
formation. The drug dissolution from solid SEDDS formulations was lower than that
of liquid SEDDS. It is possible that desorption process from the adsorbent may delay
the first step of drug dissolution. Moreover, the excipients such as fumed silica may
have a relatively strong interaction with the adsorbed SEDDS, impairing the dissolution
and extent of NDP. The percentage of NDP dissolved in SGF at 20 and 120 min is
shown in Table 3.4. The NDP dissolved from most of the formulations containing FSR
was lower than that containing FS200 at the same amount. It is likely that the viscous
oleogels of the formulations containing FSR retarded the drug dissolution from the solid
SEDDS. Furthermore, the drug dissolution was improved when the amount of FS200
was increased. This may result from the free-flowing characteristics of the solid
SEDDS obtained from the higher amount of FS200.
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Figure 3.8 Percentage of NDP released from different formulations, in simulated
gastric fluid USP without pepsin, at 37oC. Note: NDP = nifedipine; A50 = solid SEDDS
containing 50% FS200; A40 = solid SEDDS containing 40% FS200.
0
20
40
60
80
100
0 20 40 60 80 100 120
% D
rug
diss
olve
d
Time (min)
A40
A50
nifedipinepowderlipid-basedcapsule
A40
A50
NDP powder
Liquid SEDDS
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Table 3.5 Dissolution of nifedipine in SGF, after 20 and 120 min (n=3).
Sample % Drug dissolved
At 20 min At 120 min
A20 11.23 19.88
A30 11.96 19.82
A40 28.79 41.20
A50 54.00 80.05
R20 15.50 30.51
R30 11.87 15.34
R40 16.20 20.62
R50 20.51 32.80
Nifedipine powder 1.15 13.58
Liquid SNEDDS 92.89 103.35
3.4 Conclusion
The present study has demonstrated the development of the SEDDS based
on HLB of mix surfactants. Depending on the molecular structure of surfactants used,
the change of HLB affected the size of emulsion droplets after diluting in aqueous
medium. The use of polyoxyls/sorbitan monooleate blends resulted in the SEDDS that
can produce nano-sized emulsions after dilution. The selected formulation was
adsorbed on to FS200 or FSR to produce solid SEDDS. The formulations using higher
amount (30-50% w/w) of FS200 exhibited good flow properties with smooth surface
and preserved the self-emulsifying properties of liquid SEDDS. The DSC and PXRD
analysis indicated that NDP in the solid SEDDS may be in the molecular dispersion
state. In vitro dissolution study demonstrated greater drug dissolution profiles of solid
SEDDS compared with NDP. It is suggested that the NDP-loaded solid SEDDS
containing mixed surfactants for the oral administration is a promising dosage form
with good in vitro pharmaceutical results.
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CHAPTER 4
Formulation of SEDDS based on ternary phase diagram
4.1 Introduction
4.2 Materials and methods
4.2.1 Materials
4.2.2 Construction of ternary phase diagram
4.2.3 Preparation of SEDDS formulations
4.2.4 Analysis of NDP content
4.2.5 Robustness to dilution
4.2.6 Determination by small angle X-ray scattering (SAXS)
4.2.7 Transmission electon microscopic examination
4.2.8 In vitro dissolution study
4.2.9 Statistical analysis
4.3 Results and discussion
4.3.1 Construction of ternary phase diagram
4.3.2 Robustness to dilution
4.3.3 SAXS analysis
4.3.4 In vitro dissolution study
4.4 Conclusion
53
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4.1 Introduction
SEDDS can be defined as an anhydrous form of nanoemulsions. It is an
isotropic mixture of oil, surfactant, co-surfactant and drug, which spontaneously forms
thermodynamically stable oil-in-water nanoemulsions (usually with droplet size
between 100 and 300 nm) when introduced into aqueous phase under gentle agitation
conditions (7). The availability of drug for absorption can be enhanced by presentation
of the drug in solubilized form within a colloidal dispersion (4). The benefits of SEDDS
also include possibility of filling them into unit dosage forms (e.g., soft/hard gelatin
capsules), preserving physical and chemical stability upon long-term storage,
improving the bioavailability of poorly water-soluble drugs, and reducing the blood
profile variation in the patients faced with GI problem (8, 9). SEDDS can be prepared
based on hydrophilic-lipophilic balance (HLB) of surfactant or ternary phase diagram
(e.g., (56) and (57)). By using ternary phase diagram, every ratio of selected surfactant
and oil can be compared easily to select the surfactant, co-surfactant and oil
combinations. Upon contact with aqueous medium, the SEDDS formulations are self-
emulsifying and very fine dispersions (or nanoemulsions) are then formed
spontaneously (48) because the free energy required to form the emulsion is either low
and positive or negative. This dilution behavior is a characteristic for the formulations
although the final droplet size is further affected by the digestion process in the body
(28). In fact, the volume of aqueous fluid used for dilution of SEDDS may influence
the size of the emulsion droplets formed as well as the drug dissolution profile. Mostly,
the amount of aqueous fluid used for dilution study was fixed to 100 (51, 66) or 250 (5,
77) folds of the dose. Different aqueous volumes used for dilution would perhaps be
the topic for investigation, in order to ensure the robustness to dilution of the SEDDS
formulations.
The process of spontaneous emulsification proceeds through formation of
liquid crystals (LC) and gel phases. Release of drug from SEDDS is highly dependent
on LC formed at the interface, since it is likely to affect the angle of curvature of the
droplet formed and the resistance offered for partitioning of drug into aqueous media.
Currently, knowledge about the phase transition during the emulsification process of
SEDDS is rather limited. SAXS can be used to probe the structure of SEDDS. Using
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short wavelengths, λ < 10 Å, compared to the droplet size, it is possible to obtain
accurate measurements of the structure factor. Phase behavior of o/w emulsion as
spontaneous emulsion was studied after equilibrating in aqueous medium for 48 h (52,
116). However, the spontaneous emulsification of SEDDS at the time relevant to
gastric emptying (1-2 h) has not been reported.
The aim of this study was to prepare NDP-loaded SEDDS by ternary phase
diagram and investigate the physical properties and drug dissolution behavior. The
effect of volume of water used for diluting SEDDS on spontaneous emulsification was
also studied.
4.2 Materials and methods
4.2.1 Materials
Diethylene glycolmonoethyl ether; HLB 4.0 (Transcutol® HP, lot number
450829025, referred to as DGE) was a gift form Gattefosse (Saint-Priest Cedex,
France). All other materials were described in section 3.2.1.
4.2.2 Construction of ternary phase diagram
The range of the self-emulsifying formulations that could form spontaneous
emulsification under dilution and gentle agitation was identified from ternary phase
diagram of systems containing oil, surfactant and co-surfactant. A series of self-
emulsifying formulations were prepared using various concentrations of oil (CCG, 10-
98% v/v), surfactant (P35 or P40, 0-90% v/v) and co-surfactant (DGE, 2-90% v/v), at
25 C. The obtained formulations (0.1 mL) were introduced into 19.9 mL (199 folds)
of water in a test tube and then mixed gently. The tendency to spontaneously emulsify
was observed visually while the progress of emulsion droplets was observed, in
triplicate, by laser diffraction particle size analyzer (model LA-950, Horiba Ltd.,
Japan). The formulations with emulsion droplet size of 100-300 nm, resulting from
dilution, were selected for preparing of SEDDS formulations.
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4.2.3 Preparation of SEDDS formulations
According to the results from the ternary phase diagram, selected ratios of
CCG/P35/DGE and CCG/P40/DGE that provided the droplet sizes between 100 and
300 nm were used for NDP loading (80 mg/mL). The oil, surfactant and co-surfactant
were mixed at 25 C, under light protected condition, until clear solution was obtained.
Then, excess amount of NDP (500 mg) was added to the mixtures and mixed
thoroughly. The resultant formulations were shaken at 25 C for 72 h, in dark
conditions, before further analysis of NDP content. The formulations with the highest
NDP loading (dissolved NDP) were chosen for further investigation.
4.2.4 Analysis of NDP content
After equilibration for 72 h, the mixtures were centrifuged at 3,500 rpm
(1166 ×g) for 15 min to remove the undissolved NDP and supernatants were analyzed
for NDP content using high performance liquid chromatography (HPLC, model JASCO
PU-2089plus quaternary gradient inert pump, and a JASCO UV-2070plus
multiwavelength UV–vis detector, Jasco, Japan) using Luna 5u C18 column (5 μm, 4.6
nm × 25 cm) (Phenomenex, USA). The mobile phase composing of water, acetonitrile
and methanol (50:25:25) was filtered through a 0.22-μm membrane filter, and degassed
in a sonicator bath before use. The flow rate of mobile phase was 1 mL/min, and the
UV detection wavelength was 235 nm.
4.2.5 Robustness to dilution
Robustness to dilution is important for SEDDS formulation to ensure that
the emulsion formed have similar properties at different dilutions to achieve uniform
drug release behavior and that the drug will not precipitate at higher dilution in the
body, which may retard the absorption of the drug from the formulation (7).
Robustness of SEDDS formulation to dilution was studied by diluting them with water
at different dilutions (e.g., 0.01-1000 folds) and equilibrating for 30 min before
investigation. The sign of phase separation or precipitation was also observed. Droplet
size and size distribution of the formed emulsions (n=3) were investigated by photon
correlation spectroscopy (model Nano ZS, Malvern, England).
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4.2.6 Determination by small angle X-ray scattering (SAXS)
The samples for SAXS determination were prepared by diluting selected
SEDDS containing NDP (80 mg/mL) with various amounts of water or SGF (0.01,
0.02, 0.04, 0.06, 0.09, 0.11, 0.18, 0.25, 0.67, 1.5, 4, 99, 199 and 302 folds) to perform
emulsions. The obtained emulsions were incubated at 25 C for 1 or 2 h. The
experiments were performed with SAXS instrument, beamline BL2.2 : SAXS
(small/wide angle X-ray scattering), installed at Synchrotron Light Research Institute
(Public Organization), Nakhon Ratchasima, Thailand. The SAXS scattering data were
acquired using a large area pixel detector (165 mm diameter CCD; model Mar SX165,
Marresearch Ltd., USA) with pixel size of 165 mm × 165 mm. The sample was filled
into a cell placed between polyimine film (Kapton®, DupontTM, USA) window (at q
0.074-1.100 nm-1). The distance from sample to detector was 2930 mm and the X-ray
energy was 8 keV. The SAXS measurements were performed at 25 C. The raw
scattering data were background corrected, integrated and calibrated using a SAXS
Image Tool (SAXSIT) analysis suite, version 3.3 (SLRI, Thailand), which is available
at the beamline.
4.2.7 Transmission electon microscopic examination
Selected SEDDS formulations were examined under transmission electron
microscope (model JEM-1230, JOEL corp., Japan) by diluting in distilled water (199
folds) before dropping and drying on the copper grid. The samples were determined at
TEM accelerating voltage of 200 keV.
4.2.8 In vitro dissolution study
The dissolution test was examined as described in section 3.2.6.
4.2.9 Statistical analysis
Statistical analysis were carried out as described in section 3.2.7
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4.3 Results and discussion
4.3.1 Construction of ternary phase diagram
Ternary phase diagram was constructed in the absence of NDP in order to
find the self-emulsifying regions and suitable concentration of oil, surfactant and co-
surfactant. Based on the results in Chapter 3, P40 and P35 were used as surfactant,
CCG was used as oil and DGE was used as co-surfactant for constructing different
ternary phase diagrams. The spontaneous emulsifying properties were observed
visually as well as by particle size analysis. The ternary phase diagrams containing
CCG/P40/DGE and CCG/P35/DGE are presented in Figure 4.1. It was found that
incorporation of surfactant of at least 10% resulted in clear or slightly bluish emulsions
with droplet size between 100 and 300 nm while the surfactant concentration less than
10% resulted in turbid emulsions with droplet size more than 300 nm. Similar results
were observed between the two surfactants (P40 and P35). The incorporation of co-
surfactant, DGE, within the self-emulsifying region increased the spontaneity of self-
emulsifying process. Clear microemulsions with the size less than 100 nm were
obtained when concentration of CCG was 10-30% (for P40) or 10-20% (for P35).
These formulations were not select for further investigation because too high
concentration of DGE was used.
Among all formulations having the droplet size between 100 and 300 nm,
17 formulations, for each surfactant, were chosen for NDP loading, as shown in Figure
4.2. The drug loading capacity of NDP-loaded SEDDS formulation was determined
(Table 4.1). It is clearly seen that the formulations with high concentration of surfactant
(formulation 1-6 for P35 and formulation A-F for P40) and those with high
concentration of CCG (formulation 15-17 for P35 and formulation O-Q for P40) had a
low drug loading capacity (i.e., 18-35 mg/mL). Higher drug loading (35-96 mg/mL)
was obtained when the formulation with high concentration of co-surfactant (DGE),
i.e., formulation 7-14 and G-N for those using P35 and P40, respectively. The highest
drug loading (about 93-96 mg/mL) was found in formulations containing CCG
/P35/DGE of 1:1:8 and CCG/P40/DGE of 1:1:8. Zhang et al. (60) reported that the
formulation containing Labrafil® M1944 CS/P40/DGE of 3:5:3 has the highest drug
loading with a mean particle size approximately 140 nm. However, they formulated in
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Figure 4.1 Ternary phase diagrams composing of (a) CCG, P40 and DGE, (b) CCG, P35 and DGE.
(a)
(b)
P40
CCG DGE
Micromulsion (d<100 nm)
Emulsion 100 nm>d>300 nm
Emulsion (d>300 nm)
P35
CCG DGE
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Figure 4.2 Ternary phase diagrams showing the SEDDS formulations loading with
NDP; ternary phase diagram composing of (a) CCG, P40 and DGE at positions A-Q
and (b) CCG, P35 and DGE at positions 1-17.
(b) P35
CCG DGE
(a) P40
CCG DGE
A
B
F E D
Q
O
P
N M
C L K
J G H I
1
2 3
4 5 10 6 9 8 7
15
13 12 11
17 16
14
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Table 4.1 Solubility of NDP in different formulations of SEDDS (n=3)
Position CCG/P35/DGE NDP in
SEDDS
(mg/mL)
Position CCG/P40/DGE NDP in
SEDDS
(mg/mL)
1 7:3:0 20.80± .0 37 A 7:3:0 27.46±1.66
2 8:2:0 26.35±1.05 B 8:2:0 32.93± .1 80
3 7:2:1 22.77±1.86 C 7:2:1 42.94±1.16
4 9:1:0 23.08±3.24 D 9:1:0 18.61±1.28
5 8:1:1 31.76±1.03 E 8:1:1 34.27±2.70
6 7:1:2 41.11±3.01 F 7:1:2 45.40±1.28
7 4:1:5 54.98±0.13 G 4:1:5 55.31±0.61
8 3:1:6 34.56±0.14 H 3:1:6 47.69±0.05
9 2:1:7 84.87±0.67 I 2:1:7 92.35±0.40
10 1:1:8 95.83±0.35 J 1:1:8 92.63±0.51
11 3:2:5 65.58±0.52 K 3:2:5 65.40±0.42
12 2:2:6 81.03±0.35 L 2:2:6 79.97± .0 30
13 1:2:7 81.51±3.93 M 1:2:7 78.49±0.08
14 3:3:4 57.74±0.06 N 3:3:4 60.85±0.16
15 2:6:2 27.31±3.74 O 2:6:2 29.83±3.92
16 3:5:2 25.65±3.87 P 3:5:2 30.26±4.66
17 2:5:3 29.15±4.38 Q 2:5:3 35.81±5.39
Note: Solubility of NDP in P35, P40, CCG and DGE was 61.27, 67.21, 11.83 and
175.03 mg/mL, respectively.
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a narrow range of P40 (30-70%) and DGE (25-40%). It has been reported that the drug
incorporated in the SEDDS may occasionally have some effects on the self-emulsifying
performance and/or emulsion droplet size (61). However, in this study, no significant
difference was observed in self-emulsifying performance between the SEDDS and
NDP-loaded SEDDS formulations. Table 4.2 demonstrates the droplet size of SEDDS
formulations (without and with NDP loading) after diluting (199 folds) in water and
SGF. It can be seen that, after diluting in water or SGF, the droplet size of NDP-loaded
SEDDS was significantly larger than SEDDS formulation. The results are consistent
with those of other studies (51, 69) that reported the notable increase in droplet size
after drug loading in the nanoemulsions. It has been suggested that drug molecules
reduce the flexibility of surface film. Drug molecules may also participate at the
interface, resulting in closer and more compact interfacial film. Therefore, the self-
emulsification of SEDDS was hindered and nanoemulsions with larger droplet sizes
were obtained (51). However, the increase in droplet size was less affected by NDP
loading in formulation containing P35. It is possibly due to the less interfacial tension
of P35 (42.0 mN/m), compared to that of P40 (44.0 mN/m) (69, 117). SEDDS without
and with drug were examined under transmission electron microscope (Figure 4.3).
The emulsion droplet containing NDP clearly showed the existence of solid phase in
emulsion drop. Size of emulsion was confirmed by TEM that round shaped diameter
was below 200 nm as shown in TEM images.
Figure 4.3 TEM images of SNEDDS/P35 after diluting in water (199 folds); (a)
without drug, and (b) with NDP, at a magnification of 120,000x
(a) (b)
200 nm
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4.3.2 Robustness to dilution
Different fold dilutions of selected formulations were exposed to aqueous
medium to simulate the in vivo conditions where the formulation would come across
gradual dilution. Table 4.3 demonstrates the emulsion droplet size after diluting in
different amounts of water. It was found that the droplet size of emulsions decreased
when the amount of water increased except that of SEDDS/P40 diluting with 4-fold
water. However, the size of emulsion was still in nanometer range, suggesting their
robustness to dilution. At high amount of water, e.g., 500-100 folds, the droplet size
was very small and could not be measured by the equipment used. This result agreed
with Balakumar et al. (89) who reported the acceptable droplet size (nanometer range)
after dilution in 50, 100 and 1000 folds of water, providing the robustness to dilution.
Table 4.2 Droplet size of SEDDS after diluting (199 folds) in water and SGF (n=3)
Formulation Size (nm) ± S.D. (polydispersity index)
In water In SGF
SEDDS/P40 without NDP 127.6±0.9 nm (0.375) 154.9±0.1 nm (0.390)
SEDDS/P35 without NDP 129.5±0.4 nm (0.395) 124.8±0.1 nm (0.315)
NDP-loaded SEDDS/P40 187.9±5.3 nm (0.358) 185.4±0.5 nm (0.352)
NDP-loaded SEDDS/P35 132.9±0.5 nm (0.183) 132.3±0.4 nm (0.178)
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Table 4.3 Droplet size after dilution various amount of water (n=3).
Percentages
of water in
samples
Folds of
water
Size±SD (Polydispersity index)
SEDDS/P35 SEDDS/P40
1 0.01 n.d. n.d.
2 0.02 n.d. n.d.
4 0.04 n.d. n.d.
6 0.06 n.d. n.d.
8 0.09 n.d. 175.9±6.4 nm (0.390)
10 0.11 n.d. 435.3±2.4 nm (0.149)
15 0.18 n.d. 498.3±6.9 nm (0.119)
20 0.25 167.3±21.3 nm (0.350) 298.7±1.6 nm (0.166)
40 0.67 558.1±28.8 nm (0.136) 198.5±1.9 nm (0.244)
60 1.5 224.5±1.9 nm (0.193) 130.1±1.0 nm (0.317)
80 4 298.0±8.6 nm (0.669) 315.7±17.4 nm (0.669)
99 99 132.9±5.3 nm (0.158 ) 187.9±5.0 nm (0.366)
99.5 199 129.5 ±0.4 nm (0.395) 127.6 ±0.9 nm (0.375)
99.67 302 114.5±0.0 nm (0.194) 155.6±0.6 nm (0.540)
99.80 499 n.d. n.d.
99.90 999 n.d. n.d.
n.d.= not detected (due to the detection limit of the equipment)
4.3.3 SAXS analysis
The SAXS curves of SEDDS/P35 diluting with different amounts of SGF
are shown in Figure 4.4a. In distilled water, the SAXS patterns were similar to those in
SGF (Figure 4.4b). The ordered structure was not found in this study, suggesting a
simple, nano-sized, emulsion without any ordered structure. Formation of
nanoemulsions by low-energy method has been related to phase transition during the
emulsification process, involving liquid crystal phase (52). Hexagonal and lamellar
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liquid crystals are determined in nanoemulsions composing of 35% water, 65% P35,
10% CCG, and 18% water, 72% P35, 10% CCG (52). Previous study (118) suggested
that SEDDS containing resveratrol, P35, CCG and water has ordered structure with the
lamellar distances (d-spacing) of less than 20 nm. It seemed that the dilution of the
prepared SEDDS in water results in both large oil droplets (200-400 nm) in water and
small micelles with the size of 10-20 nm. Surprisingly, this was not found in the case
of formulations containing P35 (or P40), CCG and DGE. The DGE as co-surfactant
may influence the liquid crystal formation. Choi et al. (119) reported the effect of short
chain alcohols as co-surfactant on pseudoternary phase diagram, the liquid crystal
region gradually increased in longer carbon chain of alcohol molecule. The liquid
crystal regions are not observed with short chain alcohol (ethanol) in all regions of
pseudoternary phase diagram.
4.3.4 In vitro dissolution study
The dissolution profiles of NDP, NDP-loaded SEDDS/P35 and NDP-loaded
SEDDS/P40 are shown in Figure 4.5. SEDDS was immediately dispersed after capsule
shell was dissolved within 5 min, suggesting high efficiency of spontaneous dispersion.
At 60 min, the SEDDS formulation provided drug dissolution more than 80% while the
dissolution of NDP powder was less than 20%. This may be due to low free energy
required to form an emulsion of self-emulsifying systems that allowed spontaneous
formation of an interface between oil droplets and water. The drug dissolution of NDP-
loaded SEDDS/P35 provided slightly higher than the dissolution of NDP-loaded
SEDDS/P40. This result may due to the critical micelle concentration (CMC) of P35
(0.009 %w/v) are lower than P40 (0.039 %w/v). Balakrishnan et al. [30] suggested that
the mixture of oil, surfactant and co-surfactant and water phases swells, the emulsion
droplet size decreases and ultimately the drug dissolution increases. Moreover, in this
study, the improvement in NDP loading and dissolution was achieved, compared to our
previous study ; the NDP loading was increased from 30 to 80 mg/mL and the NDP
dissolution, at 60 min, was increased from about 70% to 88-98%.
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0
5E-10
1E-09
1.5E-09
2E-09
2.5E-09
3E-09
3.5E-09
4E-09
4.5E-09
0 0.2 0.4 0.6 0.8 1 1.2
Inte
nsity
(x10
-9cm
-1)
q (nm-1)
1%4%6%10%40%80%
Figure 4.4 SAXS curves of SEDDS/P35 loaded with NDP, diluted with 1, 4, 6, 10,
40 and 80 % of (a) water and (b) SGF.
0.5
1.5
2.0
2.5
3.0
3.5
4.0
4.5
1.0
0
5E-10
1E-09
1.5E-09
2E-09
2.5E-09
3E-09
3.5E-09
4E-09
4.5E-09
0 0.2 0.4 0.6 0.8 1 1.2
Inte
nsity
(x10
-9cm
-1)
q (nm-1)
1%4%6%10%40%80%
0.5
1.5
2.0
2.5
3.0
3.5
4.0
4.5
1.0
(a)
(b)
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Figure 4.5 Drug dissolution profiles of NDP powder, commercial product, NDP-
loaded SEDDS/P35, NDP-loaded SEDDS/P40.
4.4 Conclusion
SEDDS was used to improve the dissolution of NDP. After SEDDS was
diluted with water, the droplet size of about 120 nm was obtained. The non-ordered
structure was obtained after dilution at different percentages of water, according to the
scattering experiment by SAXS. The dissolution studies revealed that SEDDS
formulations attributed to higher and faster dissolution of NDP than NDP powders.
0
20
40
60
80
100
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
NDP-loaded SNEDDS/P35
NDP-loaded SNEDDS/P40
NDP powder
commercial
NDP-loaded SEDDS/P35
NDP-loaded SEDDS/P40
NDP powder
Commercial product
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CHAPTER 5
Effect of solid carrier on drug dissolution from solid SEDDS
5.1 Introduction
5.2 Materials and methods
5.2.1 Materials
5.2.2 Preparation of solid SEDDS
5.2.3 Zeta potential measurement
5.2.4 Surface free energy determination
5.2.5 Determination of emulsion droplet size
5.2.6 Morphology examination
5.2.7 Physicochemical characterization
5.2.8 In vitro dissolution evaluation
5.2.9 Stability of solid SEDDS formulations
5.2.10 Statistical analysis
5.3 Results and discussion
5.3.1 Development of solid SEDDS 5.3.2 Effect of concentration of solid carrier on drug dissolution from
solid SEDDS
5.3.3 Effect of solid carrier type on drug dissolution from solid
SEDDS
5.3.4 Stability of SEDDS and solid SEDDS formulations
5.4 Conclusion
68
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5.1 Introduction
The advent of the self-emulsification approach has reinstated the interest of
researchers for examining application of emulsions for oral drug delivery. The self-
emulsifying drug delivery system (SEDDS), an anhydrous form of emulsion, is
isotropic mixture of natural or synthetic oils, solid or liquid surfactants and alternatively
one or more hydrophilic solvents and co-solvents/co-surfactants (8, 16). SEDDS
rapidly forms a fine oil-in-water emulsion (usually with droplet size between 100 and
300 nm) when exposed to aqueous media under conditions of gentle agitation or
digestive motility that would be encountered in the GI tract (120) and thus improves
drug dissolution by providing a large surface area for partitioning of drug between oil
and GI fluids (8, 16).
However, the liquid SEDDS has limitations, for example, low drug loading
capacity, low stability, drug leakage, interaction of SEDDS with capsule shell, etc. In
order to overcome potential problems mentioned above, the liquid SEDDS is
transformed into solid dosage forms. This combines advantages of SEDDS with those
of a solid dosage form. Spray-drying and extrusion/spheronization techniques using
silicon dioxide or fumed silica (e.g., Aerosil®) as a solid carrier have generally been
employed to prepare solid dosage forms of SEDDS (55, 67). Moreover, most of the
previous studies focused on solid SEDDS prepared with silicon dioxide. In recent
years, low density porous silica (e.g., Sylysia®) has been used for solidifying the
SEDDS, in order to improve dissolution and bioavailability of poorly water-soluble
drugs such as carvedilol (75), carbamazepine (121). However, in this study, we intend
to prepare so-called solid SEDDS, a powder form of SEDDS, by physical mixing in
mortar and pestle. This technique involved adsorption of the liquid SEDDS on to solid
carriers. The major advantage of using this technique is good content uniformity and
high levels (up to 70% w/w) adsorption onto suitable carriers.
The objectives of the present study were to compare the drug dissolution
profiles of solid SEDDS prepared from different solid carriers. Drug dissolution
profiles of solid SEDDS using different solid carriers were compared and discussed in
terms of surface area, particle size and porosity of solid carriers.
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5.2 Materials and methods
5.2.1 Materials
Various types of fumed silica, i.e., Aerosil® 130 (lot number 3151072015,
referred to as FS130), Aerosil® 200 (lot number 3152082016, referred to as FS200),
Aerosil® 300Pharma (lot number 112945-52-5, referred to as FS300) Aerosil® 380 (lot
number 7631-86-1, referred to as FS380) and Aeroperl® 300 (lot number 112945-52-5,
referred to as FS300/30000) were supported by Evonik Industries (Hanua, Germany).
Porous silicon dioxide, i.e., Sylysia® 720 (lot number MD-0581, referred to as PSD700)
and Sylysia® 320, (lot number LJ-1060, referred to as PSD), were supported by Fuji
Silysia Chemical, Ltd. (Aichi, Japan). Syloid® 244 (lot number 1000204461, referred
to as PSD311) and Syloid® 72FP (lot number 100193697, referred to as PSD340) were
a gift from Grace Davison (Worms, Germany). Porous calcium silicate (Florite® RE,
lot number S20967, referred to as PCS120) was a gift from Eisai R&D Management
Co., Ltd. (Kobe, Japan). All other materials were described in section 4.2.1.
5.2.2 Preparation of solid SEDDS
SEDDS was prepared, according to section 4.2.3. To find the suitable
concentration of solid carriers in formulation, various percentages of three groups of
inert solid carriers, i.e., FS, PSD and PCS (Table 5.1) were used to develop the novel
solid SEDDS by mixing NDP-loaded SEDDS/P35 with solid carriers (20-50%) using
mortar and pestle. Table 5.2 shows the composition of SEDDS and solid SEDDS
formulations.
The angle of repose (α) was used to characterize the flow property of solid
SEDDS. The funnel was fixed at 20 cm from base and the diameter of flat base was 10
cm. The samples were placed in funnel and freely fallen. Symmetric cone on flat base
was formed. The determination of angle of repose were calculated from measured
height and base of cone, α, by the following equation.
(2)
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Among the various concentrations of solid carriers, the solid SEDDS
formulation prepared with adsorbent at concentration of 50% was selected to study the
effect of solid carrier type on drug dissolution. All inert solid carriers, i.e., FS (6
grades), PSD (4 grades) and PCS were used (Table 5.1) to prepare solid SEDDS by
mixing liquid SEDDS with solid carriers (50%) using mortar and pestle.
Table 5.1 Properties of solid carriers used in this study.
Note; n/a = not available
5.2.3 Zeta potential measurement
The zeta potential of SEDDS and solid SEDDS formulations after diluting
in water was measured by zeta potential analyzer (model Zeta Plus, Brookhaven, USA).
SEDDS and solid SEDDS formulations were dispersed in SGF (199 folds) and electric
field applied was 1 V.
Type of silica
derivatives
Code Trade name Surface
area
(m2/g)
Particle
size
(nm)
Pore size
(nm)
Oil
adsorption
(mL/100g)
Fumed silica FS130 Aerosil® 130 130 16 no pore n/a
FS200 Aerosil® 200 200 12 no pore n/a
FS300 Aerosil® 300 300 7 no pore n/a
FS380 Aerosil® 380 380 7 no pore n/a
FS300/3500 Adsolider® 101 300 3,500 no pore n/a
FS300/30000 Aeroperl® 300 300 30,000 no pore n/a
Porous silicon
dioxide
PSD300 Sylysia® 320 300 3,000 21 310
PSD311 Syloid® 244 311 3,100 19 300
PSD340 Syloid® 72 340 4,000 15 220
PSD700 Sylysia® 730 700 4,000 2.5 95
Porous calcium
silicate
PCS120 Florite® RE 120 21,600 150 4800
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Table 5.2 Composition of SEDDS and solid SEDDS formulations.
Formulation P35 (%)
P40 (%)
CCG (%)
DGE (%)
Solid carrier Amount of solid carrier (%)
NDP-loaded SEDDS/P35 10 - 10 80 - - NDP-FS130/P35/50 5 - 5 40 FS130 50 NDP-FS200/P35/20 8 - 8 64 FS200 20 NDP-FS200/P35/30 7 - 7 56 FS200 30 NDP-FS200/P35/40 6 - 6 48 FS200 40 NDP-FS200/P35/50 5 - 5 40 FS200 50 NDP-FS300/P35/50 5 - 5 40 FS300 50 NDP-FS380/P35/50 5 - 5 40 FS380 50 NDP-FS300/3500/P35/50 5 - 5 40 FS300/3500 50 NDP-FS300/30000/P35/50 5 - 5 40 FS300/30000 50 NDP-PSD300/P35/20 8 - 8 64 PSD300 20 NDP-PSD300/P35/30 7 - 7 56 PSD300 30 NDP-PSD300/P35/40 6 - 6 48 PSD300 40 NDP-PSD300/P35/50 5 - 5 40 PSD300 50 NDP-PCS120/P35/20 8 - 8 64 PCS120 20 NDP-PCS120/P35/30 7 - 7 56 PCS120 30 NDP-PCS120/P35/40 6 - 6 48 PCS120 40 NDP-PCS120/P35/50 5 - 5 40 PCS120 50 NDP-PSD311/P35/50 5 - 5 40 PSD311 50 NDP-PSD340/P35/50 5 - 5 40 PSD340 50 NDP-PSD700/P35/50 5 - 5 40 PSD700 50 NDP-loaded SEDDS/P40 - 10 10 80 - - NDP-FS130/P40/50 - 5 5 40 FS130 50 NDP-FS200/P40 /50 - 5 5 40 FS200 50 NDP-FS300/P40/50 - 5 5 40 FS300 50 NDP-FS380/P40/50 - 5 5 40 FS380 50 NDP-FS300/3500/P40/50 - 5 5 40 FS300 50 NDP-FS300/30000/P40/50 - 5 5 40 FS300 50 NDP-PSD300/P40/50 - 5 5 40 PSD300 50 NDP-PSD311/P40/50 - 5 5 40 PSD311 50 NDP-PSD340/P40/50 - 5 5 40 PSD340 50 NDP-PSD700/P40/50 - 5 5 40 PSD700 50 NDP-PCS120/P40/50 - 5 5 40 PCS120 50
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5.2.4 Surface free energy determination
The polarity and surface free energy (surface tension) of all solid SEDDS
formulations were indirectly estimated through contact angle measurement (n=3),
which was carried out by sessile drop method using a drop shape instrument (model
FTA 1000, Data Physics Corporation, USA). The percent polarity were determined
based on proportion of polarity and surface free energy of all samples, their components
and the contact angle measurement of two different standard liquids, which the values
of surface free energy and their components were known, i.e., distilled water (72.8
mN/m) and formamide (58.2 mN/m) at 25°C using Wu harmonic method equation
(122).
(3)
(1 + Cos ) = [ 4 ( )/( + ) + 4 ( )/( + ) ] (4)
where is total surface free energy of solid surface, is polarity force of solid
surface and is dispersion force of solid surface. and are polarity and dispersion
forces of standard liquid surface, respectively. is the contact angle of liquid formed
on solid surface.
5.2.5 Determination of emulsion droplet size
SEDDS and solid SEDDS formulations were diluted with water or SGF
(199 folds), and then kept for 2 h. Samples were centrifuged (666 g) for 10 min to
remove the solid carriers. Sizes of emulsion were determined using photon correlation
spectroscopy (model Zetasizer Nano ZS, Malvern, England).
5.2.6 Morphology examination
The external structure of the solid SEDDS was investigated as described in
section 3.2.5.3.
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5.2.7 Physicochemical characterization
5.2.7.1 Differential scanning calorimetry (DSC)
Thermal analysis of NDP, solid SEDDS and the physical mixture of NDP
and solid carrier was performed as described in section 3.2.5.4.1.
5.2.7.2 Powder X-ray diffractometry (PXRD)
PXRD analysis of NDP, solid SEDDS and the physical mixture of NDP
and solid carrier was examined as described in section 3.2.5.4.2.
5.2.8 In vitro dissolution evaluation
The dissolution test was carried out as described in section 3.2.6. To
understand the extent of NDP dissolution enhancement from its formulations, the
dissolution data were used to calculate the mean dissolution time (MDT). The MDT
was computed by curve fitting software, KinetDS, which is free open source software
and available at http://sourceforge.net/projects/kinetds/ (123), using following equation
(124):
(5)
where is the midpoint of the time period during which the fraction ΔQi of the drug
has been released from the dosage form, i is the dissolution sample number, and n is
the number of dissolution sampling time points.
5.2.9 Stability of solid SEDDS formulations
The solid SEDDS formulations were kept for 6 months in two conditions,
i.e., ambient condition (25°C) and stress condition (40°C/75%RH), before the
investigation of droplet size after emulsification, NDP content and dissolution. The
analysis was performed in triplicate.
5.2.10 Statistical analysis
Statistical analysis were carried out as described in section 3.2.7
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5.3 Results and discussion
5.3.1 Development of solid SEDDS
A series of SEDDS was prepared and their self-emulsifying properties were
reported in section 4.3.1. Ternary phase diagrams were constructed in the absence of
drug to identify the self-emulsifying regions and to optimize the concentrations of oil,
surfactant and co-surfactant in the SEDDS. It was found that the SEDDS containing
CCG, P35 and DGE at a ratio of 1:1:8 provides the highest NDP loading and, therefore,
was used in this chapter.
The solid SEDDS formulations were developed to overcome the
disadvantages associated with liquid SEDDS by adsorbing onto FS, PSD or PCS at
various percentages of solid carriers (Table 5.2) using mortar and pestle. The adsorbing
method used in this study was simple and required no organic solvent. In several studies
reported in literature, the lipid-based formulations were adsorbed onto solid carriers by
first dissolving them in volatile organic solvents and then adding dry carrier powders
to the solutions, followed by drying of the mixtures (125, 126). Moreover, the amount
of solid carrier adsorbed to produce the free flowing powder was not high (from 30%
solid carrier (0.6 g/g of SEDDS) to 50% solid carrier (1 g/g of SEDDS)), compared to
other report (10) that using microcrystalline cellulose (1.5 g/g of SEDDS). The low
amount of FS, PSD and PCS required to produce free flowing property may be due to
larger surface area (120-300 m2/g) of solid carriers used in this study. Powder
flowability is evaluated using the angle of repose. It is defined as the angle formed
when a cone of powder is poured on to flat surface. The excellent and good flow
properties were found in the formulation using solid carriers 30-50%. (Table 5.3). The
higher amount of solid carrier, the better powder flow ability.
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Table 5.3 The angle of repose of solid SEDDS formulations using different solid
carriers at concentration of 20-50%.
Formulation Angle of repose (o) Flow property*
FS200 27.1±0.8 excellent
NDP-FS200/P35/20 37.7±2.4 Fair
NDP-FS200/P35/30 31.4±1.5 good
NDP-FS200/P35/40 29.2±1.2 excellent
NDP-FS200/P35/50 27.2±1.4 excellent
PSD300 25.2±0.9 excellent
NDP-PSD300/P35/20 31.9±1.6 good
NDP-PSD300/P35/30 30.1±0.9 good
NDP-PSD300/P35/40 28.3±0.8 excellent
NDP-PSD300/P35/50 25.9±0.6 excellent
PCS120 25.3±1.7 excellent
NDP-PCS3120/P35/20 31.6±2.5 good
NDP-PCS3120/P35/30 29.6±1.6 excellent
NDP-PCS3120/P35/40 27.4±1.2 excellent
NDP-PCS3120/P35/50 25.6±0.9 excellent
* according to USP 29-NF 24 (127)
NDP-loaded solid SEDDS formulations were inspected for 24 h to confirm the
stability and no drug crystal was observed in the equilibrium condition. After dilution
with water and SGF (199 folds), the emulsion droplet size was less than 200 nm with a
low polydispersity index (<0.5). The zeta potential measurement was used to find the
surface charge of SEDDS and solid SEDDS formulations. The zeta potential value of
NDP-loaded SEDDS/P35 was 1 mV in water and SGF; the charge was near zero
possibly due to the large proportion of non-ionic surfactant and co-surfactant (Figure
5.1). NDP-loaded solid SEDDS formulations were more stable than NDP-loaded
SEDDS/P35 as the zeta potential values were higher (ranged from 6 to 12 mV). The
zeta potential results also suggested that the liquid SEDDS was successfully adsorbed
onto the solid carriers as evidenced by the higher surface charge of NDP-loaded solid
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SEDDS than that of solid carriers alone. The exception is for those used mesoporous
solid carrier (i.e., PCS). It is possible that, in case of NDP-PCS120/P35/50, the liquid
SEDDS was not fully adsorbed or covered on the surface of particles but might be
overlaid in the pores of PCS (Figure 5.2). Another reason is that liquid SEDDS
dispersed rapidly after dilution so the zeta potential measure is that of the PCS120
alone.
Figure 5.1 Zeta potential of solid carriers, SEDDS and solid SEDDS formulations in
(a) water and (b) SGF (n=3).
-50
-40
-30
-20
-10
0
10
20
Zet
a po
tent
ial (
mV
) ND
P-lo
aded
SED
DS/
P35
PCS1
20
ND
P- P
CS1
20/P
35/5
0
ND
P- F
S200
/P35
/50
FS20
0
-50
-40
-30
-20
-10
0
10
20
Zeta
pot
entia
l (m
V)
PCS1
20
ND
P- P
CS1
20/P
35/5
0
ND
P- F
S200
/P35
/50
PSD
300
(a) (b)
ND
P- P
SD30
0/P3
5/50
ND
P-lo
aded
SED
DS/
P35
FS20
0
PSD
300
ND
P- P
SD30
0/P3
5/50
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Figure 5.2 Schematic diagram showing the adsorption of SEDDS composing of
oil/surfactant/co-surfactant onto solid carriers and their spontaneous emulsification
after exposure to water.
5.3.2 Effect of concentration of solid carrier on drug dissolution from
solid SEDDS
The dissolution test of NDP-loaded SEDDS and NDP-loaded solid SEDDS
formulations was carried out using dissolution apparatus. Drug dissolution profiles of
SEDDS and solid SEDDS formulations in SGF are shown in Figure 5.3. The drug
NDP-PCS120/P35/50
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dissolution from NDP-loaded SEDDS/P35 was significantly higher than NDP powder
(Figure 5.3a). Drug dissolution of NDP-loaded solid SEDDS prepared with various
amounts of solid carriers, the highest drug dissolution was obtained from the
formulations using 50% solid carrier, in all solid carriers used. It is likely that high
content of solid carriers provided the large surface that allowed a greater interaction
with the dissolution medium and subsequently enhanced the drug dissolution. In case
of low amount of solid carrier, the over-wetted and large granule provided a small
surface area and then slow drug dissolution.
Different solid carriers with different properties (Table 5.1) influenced the
drug dissolution in the different extent. The NDP dissolution, at 60 min, was about
100%, 83% and 71% from solid SEDDS using 50% of PCS120, FS200 and PSD300,
respectively. FS200 gave an incomplete drug dissolution (Figure 5.3b), similar to those
reported in previous chapter (section 3.3.4). The surface charge of FS200 (and also
PSD300) was changed from negative to positive in water and to less negative in acid
condition (Figure 5.1) after mixing with SEDDS. This implied that the liquid SEDDS
adsorbed onto hydrophobic areas of the silica surface (Figure 5.2) (128), causing the
agglomeration of the particles. As a result of agglomeration, the particles could not
disperse well in the dissolution medium, especially FS200 at concentration of 20-40%;
therefore, the agglomerated FS200 hindered the dissolution of NDP-loaded
SEDDS/P35 trapped within the agglomerated particles. This may result in the slower
drug dissolution of solid SEDDS formulations containing FS200 or PSD300, as shown
in Figure 5.3. It is clearly observed that NDP-PCS120/P35/50 provided the highest
drug dissolution (Figure 5.3c), compared to that used PSD300 and FS200. It is
suggested that the solid carrier having larger surface area is considered to show lower
drug dissolution. In other words, PCS300 having smaller surface area provided a higher
dispersibility of the drug in the medium (Figure 5.3c) and consequently faster drug
dissolution. The formulations using P40 showed similar results (Figures 5.3d, e, f).
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Figure 5.3 Drug dissolution profiles of SEDDS and solid SEDDS formulations in SGF
(n=3).
(a)
(b)
(c)
0
20
40
60
80
100
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
NDP-loaded SEDDS/P35NDP-PSD300/P35/50NDP-PSD300/P35/40NDP-PSD300/P35/30NDP-PSD300/P35/20NDP powder
0
20
40
60
80
100
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
NDP-FS200/P35/50NDP-FS200/P35/40NDP-FS200/P35/30NDP-FS200/P35/20
0
20
40
60
80
100
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
NDP-PCS120/P35/50NDP-PCS120/P35/40NDP-PCS120/P35/30NDP-PCS120/P35/20
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0
20
40
60
80
100
120
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
Liquid-SEDDS/P40NDP-PSD300/P35/50NDP-PSD300/P35/40NDP-PSD300/P35/30NDP-PSD300/P35/20
0
20
40
60
80
100
120
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
NDP-FS200/P35/50 NDP-FS200/P35/40
NDP-FS200/P35/30 NDP-FS200/P35/20
0
20
40
60
80
100
120
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
NDP-PCS120/P40/50
NDP-PCS120/P40/40
NDP-PCS120/P40/30
NDP-PCS120/P40/20
Figure 5.3 (continued)
(d)
(e)
(f)
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Ito et al. (74) also reported the faster drug dissolution from the oral solid
gentamicin preparation using emulsifier and PCS120, compared to that using PSD300
or magnesium aluminometasilicate. The faster drug dissolution from NDP-
PCS120/P35/50 is possibly due to the high wettability of PCS120. This statement was
supported by the surface free energy of solid SEDDS formulations (Table 5.4). Surface
free energy is sensitive to the chemistry of the surface, the morphology and the presence
of adsorbed materials. The adsorption of liquid SEDDS on a surface can lower its
surface free energy (wettability). Solid carriers with higher surface energy (i.e.,
PCS120) have a stronger tendency to adsorb liquid SEDDS. NDP-PCS120/P35/50 also
demonstrated the highest surface energy, suggesting the formulation was easily wet in
the dissolution medium, compared to other NDP-loaded solid SEDDS formulations.
The insignificant change of the surface charge between PCS120 and NDP-
PCS120/P35/50 suggested that the adsorption might not occur on the surface of
PCS120. It is likely that the PCS120 can adsorb liquid SEDDS inside the pores,
limiting drug exposure to the surface, thus preventing drug precipitation and particle
agglomeration (121), as shown in Figure 5.3c. It is suggested that NDP-
PCS120/P35/50 demonstrated the fastest drug dissolution. From the above results, it
was found that the solid carrier at the concentration of 50% w/w produced an excellent
free-flowing solid SEDDS formulation with the highest drug dissolution and was then
used in further studies.
Table 5.4 Surface free energy of solid carriers and solid SEDDS formulations (n=3).
Surface free energy
(mN/m)
Polarity
(mN/m)
Polarity (%)
FS200 39.45±0.87 25.84±1.71 65.47±2.91
PSD300 38.16±0.52 25.42±0.12 64.77±1.21
PCS120 43.59±0.36 28.12±1.58 64.53±4.0.9
NDP-FS200/P35/50 66.67±0.37 40.75±0.77 61.11±0.81
NDP-PSD300/P35/50 65.45±1.64 40.07±0.19 60.01±1.93
NDP-PCS120/P35/50 71.80±0.12 46.13±0.14 64.25±0.09
Adhesive on glass slide (control) 39.41±0.02 21.33±0.02 54.11±0.04
Glass slide surface (control) 56.74±1.17 31.92±0.28 56.27±1.15
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5.3.3 Characterization of SEDDS and solid SEDDS
SEDDS was prepared according to section 4.2.3. Various types of solid
carrier at the concentration of 50% were used to prepare solid SEDDS. The
compositions of solid SEDDS are shown in Table 5.2. Figure 5.4 illustrates the SEM
images of different solid carriers and their corresponding solid SEDDS formulations
using P35 and P40. It is observed that NDP appeared as rectangular crystals with a
smooth compact surface. FS series were observed as aggregates of amorphous particles
with rough surfaces. Similar in morphology was observed from the solid SEDDS
formulations using FS; however, a smoother surface was seen, indicating that the liquid
SEDDS was adsorbed on the surface of FS. Moreover, no distinct crystal was detected
on the surface of aggregates after adsorbing the SEDDS on the surface of FS. The solid
SEDDS formulations prepared with PCS120 (porous calcium silicate) appeared as
rough-surfaced particles, suggesting that the SEDDS was adsorbed or coated inside the
pores of PCS. Also, the solid SEDDS prepared with PSD700 contained excipient
bridges linked with the liquid SEDDS, indicating that it produced an agglomerated solid
SEDDS. The morphology of solid SEDDS formulations using P40 showed similar
results to those using P35.
Since the physical state of NDP in the solid SEDDS would have an
important impact in the in vitro dissolution and in vivo absorption, the thermal
properties of NDP, different solid carriers, physical mixtures of NDP and solid carrier,
and solid SEDDS formulations were determined by DSC (Figure 5.5). The physical
mixtures were prepared by simply mixing the solid carriers and NDP. Pure NDP
exhibited a sharp endothermic peak at 174oC, corresponding to its melting point and
indicating its crystalline nature. All solid carriers did not show any peak over the entire
range of the tested temperature. The relative endothermic peak of NDP was remained
in the physical mixtures but relative intensity of the peak was decreased, which may be
due to dilution of the drug. No obvious endothermic peak corresponding to the melting
of crystalline NDP was found in all solid SEDDS formulations, indicating that the drug
was present in amorphous or molecularly dissolved state in solid SEDDS (51, 55). The
physical state of NDP in the solid SEDDS was further verified using PXRD
diffractograms (Figure 5.6). Pure NDP powder and physical mixtures exhibited sharp
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and highly intense diffraction peaks of drug at 2θ of 8.1°, 10.4°, 11.8°, 19.6° and 24.6°.
No obvious peaks representing crystals of NDP was observed for all NDP-loaded solid
SEDDS/P35 formulation, indicating the absence of crystalline structure of NDP in the
formulation. The NDP-loaded solid SEDDS/P40 formulations have shown similar
results.
Figure 5.4 SEM micrographs of solid carriers and solid SEDDS (1000x).
NDP-FS130/P35/50
NDP-FS200/P35/50
NDP-FS300/P35/50
FS130
FS200
NDP-FS380/P35/50
NDP-FS300/30000/P35/50
NDP-FS300/3500/P35/50
FS300
FS380
FS300/30000
FS300/3500
Fumed silica
20 μm
NDP-FS130/P40/50
NDP-FS200/P40/50
NDP-FS300/P40/50
NDP-FS380/P40/50
NDP-FS300/30000/P40/50
NDP-FS300/3500/P40/50
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Figure 5.4 (continued)
NDP-PSD340/P35/50 PSD340
NDP-PCS120/P35/50
NDP-PSD300/P35/50
NDP-PSD700/P35/50
NDP
PCS120
Porous calcium silicate
20 μm
PSD311
PSD700
PSD300
NDP-PSD311/P35/50
Porous silicon dioxide
NDP-PSD700/P40/50
NDP-PSD300/P40/50
NDP-PSD311/P40/50
NDP-PSD340/P40/50
NDP-PCS120/P40/50
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2 theta
Figure 5.5 Thermograms of NDP, solid carriers and physical mixture (PM) of NDP
and solid carriers and solid SEDDS.
Figure 5.6 Powder X-ray diffractograms of NDP, solid carriers and physical mixture
(PM) of NDP and solid carriers and solid SEDDS.
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The droplet size is a crucial factor in spontaneous emulsification
performance, because it predicts the rate and extent of drug release as well as in vivo
absorption. The smaller droplet size permits a faster release rate and provides a larger
interfacial surface area for drug absorption (129). The droplet size of emulsion
produced after diluting NDP-loaded SEDDS/P35 and NDP-loaded solid SEDDS/P35
in water or SGF was found to be in the range of 122-155 nm with low polydispersity
index while SEDDS/P40 and solid SEDDS/P40 gave mean droplet size in the range of
128-185 nm. The mean size of emulsion formed after diluting in water or SGF is given
in Table 5.5. The size of emulsion droplets formed after diluting in water was found to
be similar with that in SGF. The emulsion droplet size of formulations using P40 was
mostly bigger than that using P35. This is probably due to the difference in surfactant
molecular structure as discussed in Chapter 3. Moreover, the types of solid carrier did
not influence to the emulsion droplet size after diluting in water or SGF.
5.3.4 Effect of solid carrier type on drug dissolution from solid SEDDS
Figure 5.7 shows the dissolution profiles, in SGF, of NDP powder, SEDDS
and solid SEDDS formulations using different solid carriers. After 45 min, the drug
dissolution from NDP powder and NDP-PSD700/P35/50 were about 10% and 20%,
respectively (Figure 5.7a). The drug dissolution from NDP-FS200/P35/50 and NDP-
FS300/P35/50 was about 60%. The dissolution rate of liquid formulation, i.e., NDP-
PSD700/P35/50, was found to be higher than NDP-FS200/P35/50 and NDP-
FS300/P35/50. The porous calcium silicate-based formulation (i.e., NDP-
PCS120/P35/50), however, provided the highest drug dissolution. Similar results were
observed when P40 was used as oil component (Figure 5.7b). It is obvious that the
FS200 and PSD300 hindered the dissolution of NDP from solid SEDDS. The gelation
of silicon dioxide formed a barrier that may retard drug dissolution from the
formulations using FS200 and PSD300 (130). PCS300 having smaller surface area
provided a higher dispersibility of the drug in the medium and consequently faster drug
dissolution.
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Table 5.5 Emulsion droplet size of SEDDS and solid SEDDS formulations after
diluting in water or SGF (n=3).
Formulation Size ± S.D. (polydispersity index)
Water SGF
NDP-loaded SEDDS/P35 129.5±0.4 nm (0.395) 114.5±0.0 nm (0.204)
NDP-FS130/P35/50 132.5±0.1 nm (0.133) 145.4±0.5 nm (0.310)
NDP-FS200/P35/50 132.2±0.1 nm (0.158) 149.2±0.6 nm (0.124)
NDP-FS300/P35/50 132.9±0.5 nm (0.183) 155.4±0.5 nm (0.352)
NDP-FS380/P35/50 128.9±0.5 nm (0.177) 155.2±0.5 nm (0.312)
NDP-FS300/3500/P35/50 133.9±0.4 nm (0.197) 139.4±0.4 nm (0.127)
NDP-FS300/30000/P35/50 122.0±0.2 nm (0.183) 150.4±0.5 nm (0.252)
NDP-PSD300/P35/50 132.9±0.1 nm (0.143) 130.4±0.1 nm (0.132)
NDP-PSD311/P35/50 129.8±0.1 nm (0.177) 133.1±0.4 nm (0.222)
NDP-PSD340/P35/50 128.9±0.2 nm (0.103) 130.2±0.3 nm (0.130)
NDP-PSD700/P35/50 129.8±0.1 nm (0.143) 131.2±0.4 nm (0.142)
NDP-PCS120/P35/50 131.9±0.1 nm (0.123) 135.4±0.5 nm (0.132)
NDP-loaded SEDDS/P40 127.6±0.9 nm (0.375) 154.9±0.1 nm (0.390)
NDP-FS130/P40/50 167.9±3.3 nm (0.255) 165.4±0.5 nm (0.242)
NDP-FS200/P40 /50 187.9±5.3 nm (0.358) 185.4±0.5 nm (0.352)
NDP-FS300/P40/50 169.8±1.2 nm (0.285) 161.4±0.4 nm (0.293)
NDP-FS380/P40/50 178.5±1.3 nm (0.381) 171.4±0.7 nm (0.303)
NDP-FS300/3500/P40/50 179.5±1.0 nm (0.301) 169.3±0.6 nm (0.271)
NDP-FS300/30000/P40/50 168.3±1.7 nm (0.271) 177.3±0.2 nm (0.269)
NDP-PSD300/P40/50 170.3±1.5 nm (0.301) 169.5±0.4 nm (0.321)
NDP-PSD311/P40/50 177.3±1.1 nm (0.291) 170.1±0.3 nm (0.201)
NDP-PSD340/P40/50 175.3±0.7 nm (0.321) 174.7±0.5 nm (0.351)
NDP-PSD700/P40/50 172.3±0.5 nm (0.225) 173.5±0.7 nm (0.231)
NDP-PCS120/P40/50 169.2±0.3 nm (0.251) 170.3±0.2 nm (0.239)
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Figure 5.7 Dissolution profiles in SGF of NDP, SEDDS and solid SEDDS
formulations using different solid carriers; (a) P35 and (b) P40 (n=3).
0
20
40
60
80
100
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
0
20
40
60
80
100
0 20 40 60 80 100 120
Dru
g di
ssol
ved
(%)
Time (min)
(b)
(a)
NDP-loaded SEDDS/P35 NDP-PCS120/P35/50 NDP-FS200/P35/50 NDP-PSD300/P35/50 NDP-PSD700/P35/50 NDP powder
NDP-loaded SEDDS/P40 NDP-PCS120/P40/50 NDP-FS200/P40/50 NDP-PSD300/P40/50 NDP-PSD700/P40/50
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The MDT, which is the arithmetic mean value of dissolution profile, reflects
the time for the drug to dissolve and is first statistical moment for the cumulative
dissolution process that provides an accurate drug release rate (124). A lower MDT
value indicates faster dissolution rate. The MDT calculated from the drug dissolution
profiles of SEDDS was about 18.1 min and 13.9 min for NDP-loaded SEDDS/P35 and
NDP-loaded SEDDS/P40, respectively. Table 5.6 demonstrates the MDT of different
solid SEDDS formulations containing P35 or P40. It is evident that different solid
carriers having different surface areas or pore sizes influenced the MDT of solid
SEDDS formulations. The MDT of solid SEDDS formulations containing both P35 and
P40, using non-porous solid carriers (i.e., FS), was in the order of FS200 < FS380 <
FS300/30000 < FS300 < FS300/3500 < FS130. The linear relationship between the
MDT of solid SEDDS formulations and the surface area of solid carriers was also
investigated. The correlation coefficient (r) of about 0.73-0.77 was observed, implying
the moderate correlation between MDT and surface area of non-porous solid carriers.
The result is in agreement with the study of Agarwal et al. (72) who reported that the
drug dissolution from adsorbed SEDDS on carrier is found to be dependent on surface
area of solid carriers. The dissolution rate increases with an increase in surface area
and is independent of the chemical nature of the adsorbents (72). The dissolution
profiles of controlled release lipid microparticles containing solid carriers (e.g., FS200
and FS300) appear to be closely related to the physicochemical properties of solid
carriers, especially to their gelation properties, which are a function of its specific
surface area; the drug dissolution decreases with an increase in surface area of solid
carrier (130). The MDT of solid SEDDS formulations containing both P35 and P40,
using porous solid carriers (i.e., PSD and PCS) was in the order of PCS120 < PSD311
< PSD340 < PSD300. For the formulations using PSD700, the MDT could not be
calculated as the drug dissolution was incomplete; only about 30% of NDP was
dissolved within 120 min. It is apparent that the drug dissolution from the formulations
using PSD700 was retarded by gelation of PSD700, as confirmed in Figure 5.4. For
porous solid carriers, the results indicated that NDP dissolution was influenced by pore
size of solid carriers. It is quite difficult for SEDDS to enter inside the very small pores
(ranged from 15 to 21 nm) of PSD300, PSD311, and PSD340; therefore, the outer
surface of silica particles were covered with SEDDS and subsequently provided limited
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surface area for drug dissolution. On the other hand, PCS120, which has the particle
size of 21.6 μm and pore size of 150 nm, offered larger pores allowing SEDDS to enter
and fill in the pores of PCS120. This resulted in a higher dispersibility of the drug in
the medium after dilution and consequently faster drug dissolution. These results were
also supported by the study of Ito et al. (74) who reported that the oral solid gentamicin
preparations using emulsifier and containing large-pore adsorbent (PCS120) provided
higher drug dissolution than those containing PSD300 and Neusilin® US2 (pore size of
21 and 50 nm, respectively).
For porous solid carriers, the degree of linear relationship between MDT
and surface area was very low (i.e., r less than 0.1), suggesting no correlation between
MDT and surface area of porous solid carriers. In contrast, the strong correlation (r of
about 0.78-0.80) between MDT and pore size of porous solid carriers was observed.
Similar results were reported by Gao et al. (131) and Jia et al. (132). The dissolution of
drug is improved and the dissolution rate can be controlled by the pore size of solid
carriers.
Table 5.6 Mean dissolution time of SEDDS and solid SEDDS using several types of
solid carrier at 50% in the formulations and containing P35 or P40 (n=3).
Formulation Mean dissolution time ± S.D. (min) P35 P40
NDP-loaded SEDDS 18.1±0.8 13.9±1.1 FS130 37.2±1.4 40.3±6.1 FS200 14.1±0.2 14.5±1.0 FS300 20.1±1.2 20.9±2.6 FS380 14.3±1.8 18.3±2.1 FS300/3500 25.3±4.9 24.4±2.1 FS300/30000 15.0±3.7 18.9±1.3 PSD300 41.7±4.0 41.3±3.1 PSD311 20.7±0.5 21.0±2.9 PSD340 17.6±0.4 28.0±3.2 PSD700 n/a n/a PCS120 4.8±1.4 7.1±0.9
Note; n/a = not applicable
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5.3.4 Stability of SEDDS and solid SEDDS formulations
The stability of NDP in selected formulations was evaluated in term of the
emulsion droplet size after diluting in water or SGF, drug content and MDT of SEDDS
or solid SEDDS formulations under accelerated stress conditions of 40°C/75%RH for
6 months. The real-time stability at ambient condition (25°C) was also studied. Table
5.7 demonstrates the stability test results of different formulations containing P35. Both
SEDDS and solid SEDDS did not show any physical change during the study period.
Drug content of SEDDS/P35, FS200/P35 and PCS120/P35 before the stability test was
100.00±0.42%, 100.00±0.21% and 100.00±0.54%, respectively. Drug content was
found to be more than 99% at the end of 6 months in both accelerated and long-term
conditions. No significant drug loss was observed from the formulations tested.
Generally, solid SEDDS formulations possess the risk of in vivo drug
precipitation upon dilution in stomach and intestine which can lead to failure in
bioavailability enhancement. The stability of the selected solid SEDDS formulations
was evaluated by diluting 199 times in each case with water or SGF, and measuring the
emulsion droplet size (Table 5.7). It was found that the droplet size of all formulations
was still less than 200 nm (127-139 nm), similar to the initial day. Polydispersity index
in each case was also extremely low. The experiment confirmed that the selected
formulations had no effect upon dilution and were stable in both water and acidic
condition (in SGF). It is likely that the surfactant/co-surfactant used in the formulation
brought sufficient reduction in free energy of the system to resist thermodynamic
instability.
The physicochemical properties, i.e., DSC and PXRD, of selected solid
SEDDS formulations after keeping in accelerated and long-term conditions for 6
months were also investigated. No endothermic peak corresponding to the melting of
crystalline NDP was found, by DSC, in all solid SEDDS formulations after 6-month
storage in both conditions (Figure 5.8). The PXRD results also showed the halo-type of
amorphous solid for all solid SEDDS formulations after 6-month storage in both
conditions, indicating the absence of crystalline structure of NDP in the formulation
(Figure 5.9). This is similar to the PXRD patterns of solid SEDDS formulations before
stability test. The dissolution properties of the solid SEDDS formulations kept for 6
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months in both conditions were similar to those of freshly prepared solid SEDDS
formulations. The MDT of all solid SEDDS formulations kept in both storage
conditions was nearly the same as that of freshly prepared solid SEDDS formulations.
These results indicated the effectiveness of solid SEDDS to maintain the dissolution
properties over 6 months when storage in both accelerated and long-term conditions.
Table 5.7 Stability test results of selected SEDDS and solid SEDDS formulations containing P35 (n=3). SEDDS/P35 FS200/P35 PCS120/P35
Initial day
Size after diluting in water ± S.D.
(nm) [Polydispersity index]
192.5±0.4
[0.950]
132.2±0.1
[0.158]
131.9±0.1
[0.123]
Size after diluting in SGF ± S.D.
(nm) [Polydispersity index]
114.5±0.0
[0.204]
149.2±0.6
[0.124]
135.4±0.5
[0.132]
Mean dissolution time ± S.D. (min) 18.1±0.8 14.1±0.4 4.8±1.4
Drug content ± S.D. (%) 100.00±1.21 100.00±0.56 100.00±0.78
Accelerated stability testing
Size after diluting in water ± S.D.
(nm) [Polydispersity index]
132.5±0.3
[0.360]
135.2±0.1
[0.130]
133.8±0.1
[0.110]
Size after diluting in SGF ± S.D.
(nm) [Polydispersity index]
127.5±0.0
[0.210]
138.2±0.5
[0.130]
132.3±0.4
[0.140]
Mean dissolution time ± S.D. (min) 20.8±4.9 14.4±0.7 5.8±0.1
Drug content ± S.D. (%) 99.84±0.21 100.00±0.25 99.90±0.22
Long-term stability testing
Size after diluting in water ± S.D.
(nm) [Polydispersity index]
131.7±0.4
[0.350]
132.2±0.2
[0.110]
137.1±0.3
[0.120]
Size after diluting in SGF ± S.D.
(nm) [Polydispersity index]
130.1±0.0
[0.240]
135.2±0.2
[0.120]
135.1±0.3
[0.130]
Mean dissolution time ± S.D. (min) 22.7±3.9 14.6±0.5 5.6±0.3
Drug content ± S.D. (%) 99.86±0.50 99.96±0.64 100.13±0.50
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Figure 5.8 Thermograms of NDP, solid carriers and physical mixture (PM) of NDP
and solid carriers and solid SEDDS, solid SEDDS under accelerated stress condition;
NDP-PCS120/P35/50/Ac, NDP-FS200/P35/50/Ac, NDP-PSD700/P35/50/Ac and
long-term condition study; NDP-PCS120/P35/50/Lo, NDP-FS200/P35/50/Lo, NDP-
PSD700/P35/50/Lo
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Figure 5.9 Powder X-ray diffractograms of NDP, solid carriers and physical mixture
(PM) of NDP and solid carriers, solid SEDDS under accelerated stress condition; NDP-
PCS120/P35/50/Ac, NDP-FS200/P35/50/Ac, NDP-PSD700/P35/50/Ac and long-term
condition study; NDP-PCS120/P35/50/Lo, NDP-FS200/P35/50/Lo, NDP-
PSD700/P35/50/Lo
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5.4 Conclusion
The solid SEDDS formulations were developed using various types of solid
carriers, i.e., FS, PCS and PSD. Drug dissolution was found to depend on the type of
solid carriers and pore size at the liquid SEDDS/solid carrier interface. Among the
solid SEDDS formulations tested, the solid SEDDS formulation prepared with PCS at
the concentration of 50% (i.e., PCS120/P35/50) showed the highest dissolution rate.
PCS also had significant and positive effect on crystalline properties of drug-loaded
solid SEDDS formulations. PCS120/P35/50 improved the dissolution rate of drugs
tested due to the fast self-emulsion formation. The stability of NDP in selected
formulations was evaluated. No significant drug loss was observed from the
formulations tested. The results shown the effectiveness of solid SEDDS to maintain
the dissolution properties over 6 months when storage in both accelerated and long-
term conditions.
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CHAPTER 6
Effect of dietary state on oral bioavailability of nifedipine by SEDDS
6.1 Introduction
6.2 Materials and methods
6.2.1 Materials
6.2.2 Preparation of solid SEDDS formulations
6.2.3 In vivo absorption study in rats
6.2.4 Statistical analysis
6.3 Results and discussion
6.3.1 In vivo absorption study in rats
6.4. Conclusion
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6.1 Introduction
The in-vitro evaluation of SEDDS was used to compare the developed
products, assess batch-to-batch consistency and to ensure the performance of the
formulation. With appropriate method, in vitro dissolution may be correlated with in
vivo performance and employed as a surrogate for bioequivalence study. Although, the
conventional USP dissolution evaluation is required as a quality control tool for
pharmaceutical products, it is rarely appropriate for predicting in-vivo performance of
SEDDS since the dissolution of drug and GI processing of lipid vehicle (including
digestion and dispersion) are intrinsically associated to each other (33). In particularly,
lipids and lipid-based ingredients are subject to digestion occurring in GI tract. Gastric
and pancreatic lipases can metabolize glycerides as well as other esters of fatty acids
and alcohol, e.g., PEG esters contained in polyoxyglycerides. Lipase may also
influence the dispersion of SEDDS properties of fatty acid esters, hence altering their
solubilization capability in-vivo. For these causes, the development of SEDDS products
has been required the in vivo studies.
A number of experiments have been published where SEDDS increased the
bioavailability of a BCS Class II compounds (133, 134) but a limited number of
publications have shown how these systems behave with concurrent food intake. The
effect of food on drug absorption should be investigated and compared with the fasted
condition in animals or in clinical tests. Nielsen et al. (135) found no significant food
effect on probucol in mini-pigs when formulated in lipid-based formulations. Woo et
al. (136) administered itraconazole formulated as self-microemulsifying drug delivery
systems (SMEDDS) in capsules to eight healthy volunteers in both fed and fasted states
and found a pronounced food effect on itraconazole absorption from Sporanox® capsule
(commercial product). The influence was less pronounced for the SMEDDS containing
itraconazole.
The objective of the present study was to compare the drug absorption of
NDP-loaded solid SEDDS prepared from different solid carriers. The influence of food
intake on drug absorption in rats was also investigated.
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6.2 Materials and methods
6.2.1 Materials
All materials used in this chapter were described in section 5.2.1.
6.2.2 Preparation of solid SEDDS formulations
Selected SEDDS and solid SEDDS formulations (Table 6.1) were prepared
as described in section 5.2.2.
Table 6.1 The composition of SEDDS and solid SEDDS formulations.
Formulation CCG P35 DGE FS200 PCS120
NDP-loaded SEDDS/P35 10% 10% 80% 0% 0%
NDP-FS200/P35/50 5% 5% 40% 50% 0%
NDP-PCS120/P35/50 5% 5% 40% 0% 50%
6.2.3 In vivo absorption study in rats
The in vivo absorption of NDP from solid SEDDS formulations (FS200/P35
and PCS120/P35) was compared to that of NDP powder and commercial product (lot
number 11017C, Berlin Pharmaceutical Industry Co. Ltd., Thailand). The in vivo
studies were modified form the study of Burapapadh and coworkers (137). The
experiments were performed in male Wistar rats (8 weeks, 300-350 g, Southern
Laboratory Animal Facility, Prince of Songkla University, Thailand) and less than 3
rats per cage were stored, subjected to 12 h – 12 h cycles of light and darkness, with
free access to food and water. The rats were divided into 2 groups, i.e., fasting group
and feeding group. In case of fasting group, the rats were fasted for 24 h before
experiment in order to avoid food influence on drug absorption. The rats were
administrated with the formulation at a dose of 10 mg of NDP/kg body weight (n= 5).
Before administration to rats, the samples, equivalent to 5 mg of NDP, were dispersed
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in 1 mL of 0.5% (w/v) sodium carboxymethylcellulose solution by vortexing the
mixtures for 5 min. Then, 1 mL of dispersion composing of NDP (5 mg/mL) was orally
administered into rats. Before collecting the blood sample, the catheters were flushed
with heparin solution not more than 1 day. Blood samples of approximately 600 μL
were collected from the jugular vein at 0, 0.5, 1, 2, 4, 6, 12, and 24 h after dosing, and
then placed into microcentrifuge tubes with light protection. The collected samples
were centrifuged at 10,000 rpm (3330 g) for 5 min, and then plasma was extracted and
transferred to a microcentrifuge tube. All samples were kept at -20°C before drug
content determination with HPLC (137).
Prior to HPLC analysis, plasma was removed from the frozen samples and
allowed to equilibrate to room temperature. The 200 μL of plasma were placed to
another tube and the protein was precipitated by adding 800 μL of acetonitrile and
mixed by vortex mixer for a minute. The mixtures were held still for 20 min before
evaporation of solvent. The precipitates were dissolved in 150 μL of methanol and then
determined the drug content by HPLC. The area under the plasma concentration-time
curve (AUC) was calculated. The samples were analyzed by a HPLC (model Agilent
1100 Series HPLC System equipped with a photodiode array detector, Agilent
Technologies, USA) using Luna 5u C18 column (5 μm, 4.6 nm 25 cm)
(Phenomenex®, USA). The analysis methods were applied form the studies reported (138, 139). The solvent system composed of solvent A (100% methanol) and solvent B
(0.05% phosphoric acid). A 30-min linear gradient from 70% B to 0% B was applied
at a flow rate of 1 mL/min, followed by a 10-min isocratic elution at 0% B and then a
10-min wash at 0% B, before return to the starting condition. NDP was detected by
monitoring of UV absorbance at 235 nm, and it was quantified by comparison of peak
areas to a standard curve. All experiments were approved by the ethics committee for
the use of laboratory animals, Faculty of Pharmacy, Silpakorn University, under the
permission number 001/2013 and monitored by Department of Physiology, Faculty of
Science, Prince of Songkla University.
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6.2.4 Statistical analysis
Statistical analysis was carried out as described in section 3.2.7.
6.3 Results and discussion
6.3.1 In vivo absorption study in rats
The formulation effect on the pharmacokinetics of NDP given orally was
evaluated in rats and the results are shown in Figure 6.1 and Table 6.2. It is well-known
that the intake of food concurrent to lipophilic drugs can improve drug absorption
significantly. Therefore, in this study, the effect of food in absorption from SEDDS or
solid SEDDS formulations was investigated. Selected formulations were tested in both
fasted and fed rats. The in vivo plasma concentration-time profiles after oral
administration of SEDDS and solid SEDDS to fasted rats are demonstrated in Figure
6.1a. Administration of the NDP powder led to fairly low plasma concentrations. The
median Tmax for NDP powder formulation was 1 h, ranging from 0.5 to 2 h. The Cmax
and AUC of NDP powder were about 1,146 ng/mL and 1,413 ng h/mL, respectively.
The AUC of commercial product was slightly higher than that of NDP powder. This is
probably that the commercial product was available as liquid formulation which can
provide higher drug dissolution and drug absorption. All SEDDS and solid SEDDS
formulations investigated in this study improved the AUC of NDP significantly,
compared with the NDP powder in fasted rats (Table 6.2), that is 2.9, 6.8 and 7.1 folds
for SEDDS/P35, FS200/P35 and PCS120/P35, respectively. All SEDDS and solid
SEDDS formulations also showed significantly higher Cmax than NDP powder but no
difference in the median Tmax. It is apparent that an increase in drug absorption of
SEDDS, compared to NDP powder, was fairly low (2.9 folds for AUC). It is possible
that digestion of lipid in the formulation could reduce the solubility of NDP in the gut
lumen, which would result in precipitation of the drug and a decrease in the absorption
rate (140). Compared to the solid SEDDS formulations, SEDDS was found to exhibit
a lower AUC. No significant difference in AUC between solid SEDDS formulations
using different solid carriers (i.e., FS200 or PCS120) was observed though the PCS120
exhibited slightly higher AUC than FS200. Moreover, PCS120 also demonstrated the
highest Cmax. PCS in the formulations may provide a higher dispersibility of the NDP
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Figure 6.1 In vivo plasma profiles of commercial product, NDP-loaded SEDDS/P35,
NDP-PCS120/P35/50 and NDP-FS200/P35/50 and the NDP powder in the (a) fed and
(b) fasted conditions (n=5).
NDP-FS200/P35/50
NDP powder
Commercial product
NDP-loaded SEDDS/P35
NDP-PCS120/P35/50
NDP-FS200/P35/50
NDP-loaded SEDDS/P35
NDP-PCS120/P35/50
NDP powder
Commercial product
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Table 6.2 Pharmacokinetic parameters of SEDDS and solid SEDDS formulations in the fasted and fed conditions in vivo (n=5).
Fasted condition Fed condition AUC ratio
(Fed/Fasted) AUC0-12h (ng·h/mL) ± SE Tmax
(h)* Cmax
(ng/mL) ± SE AUC0-12h (ng·h/mL) ± SE Tmax
(h)* Cmax
(ng/mL) ± SE
NDP powder 1413.4 ± 388.4 1 [0.5-2] 1145.9 ± 664.8 2487.8 ± 497.4 1 [0.5-2] 725.2 ± 131.1 1.8
NDP-loaded SEDDS/P35 4082.6 ± 621.7 1 [0.5-2] 1857.8 ± 585.5 11718.4 ± 599.9 2 [2-4] 2660.9 ± 180.3 2.9
NDP-FS200/P35/50 9651.3 ± 723.6 2 [1-2] 1707.6 ± 102.3 7628.2 ± 444.5 4 [1-4] 1496.9 ± 394.6 0.8
NDP-PCS120/P35/50 9998.3 ± 599.0 2 [2] 2367.9 ± 113.6 14147.0 ± 719.6 1 [1-2] 2636.0 ± 274.5 1.4
Commercial product 1880.0 ± 244.4 2 [1-2] 706.6 ± 35.5 3053.5 ± 1006.9 1 [1] 956.7 ± 258.2 1.6
* Median range in brackets
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in the medium, a faster drug dissolution and subsequently a higher drug absorption. In
vivo plasma concentration-time profiles following oral administration to fed rats are
shown in Figure 6.1b. The absorption of NDP powder under fed condition was higher
than those under fasted condition. It is possible that NDP, a poorly water-soluble
lipophilic compound, was emulsified into small lipid droplets in the stomach and further
incorporated into mixed micelles by the action of bile salts (140). Solid SEDDS
formulations that rely on their own spontaneous emulsifying abilities presented the
enhanced absorption of NDP in rats. As shown in Table 6.2, the solid SEDDS
formulations containing PCS120 exhibited a slightly faster absorption compared to the
SEDDS and other solid SEDDS formulations and noticeable faster than NDP powder.
No significant difference was observed between the median Tmax in the fed rats. The
Cmax after administration of solid SEDDS formulations was found to be significantly
higher than that of the NDP powder and commercial product (Table 6.2). The AUC
values of NDP were in the order of PCS120/P35 > SEDDS/P35 > FS200/P35 >
commercial product > NDP powder. The marked increase in the absorption rate of NDP
from PCS120/P35 may be due to the increased drug dissolution from solid SEDDS
formulations and can then enhance the oral bioavailability of NDP.
Table 6.2 also demonstrated that the plasma NDP concentrations under fed
condition were higher than those under fasted condition. The result suggested that food
effect on bioavailability of NDP appeared to be significant. Specially, the NDP powder,
commercial product and SEDDS/P35 revealed a higher AUC ratio (i.e., 1.6-2.9),
compared to solid SEDDS formulations. The results are in agreement with Ueno et al.
(141) who reported that the food increases the bioavailability (AUC ratio of 1.31) NDP
sustained release preparation. Similar results were reported by Kawakami et al. (142)
who found that the oral absorption of nitrendipine reveals a pronounced food effect
when administered as a suspension in fed rats as compared to fasted rats. The AUC
ratio of NDP was 0.8 and 1.4 for FS200/P35 and PCS120/P35, respectively. It is
suggested that the reduction of food effect on drug absorption was found when using
solid SEDDS formulations. Nielsen and co-workers (135) have reported that probucol
shows no significant food effect, when formulated in a lipid and surfactant based
formulations
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6.4. Conclusion
In this study, solid carriers (particularly porous calcium silicate) had
significant and positive effect in oral bioavailability of NDP in the solid SEDDS.
Comparing the absorption (i.e., AUC) in the fasted and fed rats, NDP powder and
commercial products exhibited a significant food effect. The difference in
bioavailability of NDP in fed compared to fasted state can be avoided by using solid
SEDDS formulations.
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CHAPTER 7
Effect of drug lipophilicity on dissolution of drug-loaded solid SEDDS
7.1 Introduction
7.2 Materials and methods
7.2.1 Materials
7.2.2 Preparation of solid SEDDS formulations
7.2.3 Physicochemical characterization
7.2.3.1 DSC
7.2.3.2 PXRD
7.2.4 Analysis of drug content
7.2.5 In vitro drug dissolution test
7.3 Results and discussion
7.3.1 Characterization of drug-loaded SEDDS
7.3.2 In vitro drug dissolution
7.4. Conclusion
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7.1 Introduction
Drugs with low solubility present a major problem during formulation of
SEDDS (24). The semi-synthetic hydrophilic oils and surfactants usually dissolve
hydrophobic drugs to a greater extent than conventional oils. The addition of solvents
i.e., ethanol, PG and PEG, may also contribute to the improvement of drug solubility in
the lipid vehicle. The ability of drug incorporation into a SEDDS is generally specific
to each case depending on the physicochemical compatibility of the drug. In most cases,
the physical properties of the drug influence to formation of emulsion, leading to a
change in the optimal oil/surfactant ratio. The efficiency of a SEDDS can be altered
either by interaction with the LC phase (49), or by penetration into the surfactant
interface (143). The interference of the drug compound with the self-emulsification
process may result in a change in droplet size distribution that can vary as a function of
drug concentration (120, 143). It is suggested that the only one universal SEDDS
formulation was not solved the problem of poorly water-soluble drugs (144).
The formulation abilities of 10 drugs with SMEDDS (4 systems) were
reported by Thi et al. (145). Grisiofluvin and itraconazole have been felted in the
development by limitation of drug solubility. Methylprednisolone, fenofibrate and
danazole are formed SMEDDS with only two systems. The other 5 drugs which can
form SMEDDS with all 4 systems. It is obvious that the drug compounds should first
be able to dissolve in surfactants and oils to formulate a SMEDDS.
One of the limitations of SEDDS formulations is that different poorly water-
soluble drugs behave differently in similar vehicles, thus highlighting the need to assess
candidate compounds on an individual basis. To the best of our knowledge, a very few
published reports has assessed the effect of physicochemical properties of different
poorly water-soluble drugs on the dissolution behavior of SEDDS formulations.
Therefore, in this study, the effect of drugs with similar structure but different
lipophilicity (LogP), that is, nifedipine (NDP), felodipine (FDP), manidipine (MDP)
and itraconazole (ITZ), on dissolution was investigated.
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7.2 Materials and methods
7.2.1 Materials
Felodipine (lot number 20090502, referred to as FDP, LogP 4.46) was
purchased from Xilin Pharmaceutical Raw Material Co., Ltd (Jiangsu, China).
Manidipine dihydrochloride (lot number 07100825, referred to as MDP, LogP 5.46)
was supported by Sriprasit Pharma Co., Ltd. (Bangkok, Thailand). Itraconazole (lot
number ITD0511008, referred to as ITZ, LogP 5.66) was purchased from Megafine
Pharma Co., Ltd. (Mumbai, India). The properties and chemical structure of the drugs
studied are shown in Figure 7.1. All other materials were described in section 5.2.1.
7.2.2 Preparation of solid SEDDS formulations
A mixture of P35 (or P40), CCG and DGE at a ratio of 1:1:8 was prepared
as described in section 4.2.3, at ambient temperature (25°C). The solubility of FDP,
MDP and ITZ was determined in the mixture as described in section 3.2.2. To
investigate the effect of drugs with different lipophilicity (LogP), SEDDS was loaded
with NDP, FDP, MDP and ITZ, at concentration of 80 mg/mL, 10 mg/mL, 15 mg/mL
and 3 mg/mL, respectively, according to their solubility in SEDDS. SEDDS containing
drugs was subsequently mixed with PCS120 (50%) using mortar and pestle to obtain
drug-loaded solid SEDDS.
7.2.3 Physicochemical characterization
7.2.3.1 DSC
Thermal analysis of drug, solid SEDDS and the physical mixture of drug
and solid carrier was performed as described in section 3.2.5.4.1.
7.2.3.2 PXRD
PXRD analysis of samples were examined as described in section 3.2.5.4.2.
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Properties Chemical structure
Nifedipine (NDP) MW = 346.34 g/mol
LogP = 2.50
pKa = 3.93
Felodipine (FDP) MW = 384.20 g/mol
LogP = 4.46
pKa = 5.07
Manidipine (MDP) MW = 647.17 g/mol
LogP = 5.46
pKa = 9.4
Itraconazole (ITZ) MW = 705.63 g/mol
LogP = 5.66
pKa = 3.7
Figure 7.1 Properties and structure of various poorly water-soluble drugs used in this
study.
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7.2.4 Analysis of drug content
NDP content in SEDDS and solid SEDDS formulations was analyzed with
a high performance liquid chromatography, HPLC (model JASCO PU-2089plus
quaternary gradient inert pump, and a JASCO UV-2070plus multiwavelength UV–vis
detector, Jasco, Japan), using Luna 5u C18 column (5 μm, 4.6 nm 25 cm)
(Phenomenex®, USA). The flow rate of mobile phase (water, acetonitrile and methanol
at a ratio of 50:25:25) was 1 mL/min and the detection wavelength was 235 nm. The
content of MDP, FDP and ITZ were also analyzed using the HPLC at detection
wavelength of 228, 254 and 263 nm, respectively. The mobile phase for MDP was
changed to pH 4.6 phosphate buffer:acetonitrile (49:51) while that for FDP was
changed to phosphatebuffer: acetonitrile: methanol (40:40:20). The mobile phase for
ITZ consist of acetonitrile: water: diethylamine (63:37:0.05) adjusting pH to 2.45 with
phosphoric acid.
7.2.5 In vitro drug dissolution test
The dissolution test of SEDDS containing NDP, MDP, FDP and ITZ
(equivalent to drug 10, 3, 10 and 0.3 mg, respectively) was carried out as described in
section 3.2.6.
7.3 Results and discussion
7.3.1 Characterization of drug-loaded SEDDS
Different drugs, i.e., NDP, FDP, MDP and ITZ (Figure 7.1) were loaded in
selected SEDDS, consisting of CCG, P35and DGE at a ratio of 1:1:8. The solubility of
NDP, FDP, MDP and ITZ are 98.83±0.35, 10.36±0.86 mg/mL, 15.58±0.25 mg/mL and
3.45±0.17 mg/mL, respectively. The drug-loaded SEDDS was adsorbed onto PCS120
(at 50% of solid carrier). The self-emulsifying properties of different drug-loaded
SEDDS and solid SEDDS formulations were visually observed. It has been reported
that drug incorporation in the SEDDS may have some effects on its self-emulsifying
performance (145). However, in this study, no significant difference was found in the
self-emulsifying performance when compared to the corresponding formulations
containing different drugs. Moreover, the average droplet size of all formulations were
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found to be less than 200 nm with low polydispersity index (<0.5), irrespective of the
type of drug and the pH of the medium (Table 7.1). The consistency on the emulsion
droplet size obtained after dilution implied that the formulations were stable in the GI
tract and that the SEDDS can be applied to different drugs. Besides, small droplet size
leads to larger interfacial surface area for drug absorption (88).
The scanning electron micrographs of PCS120/P35/50 loading with
different drugs are shown in Figure 7.2. It is evident from this Figure that PCS120 is
granular and highly porous material with small (nano-sized) pores. The appearance of
the PCS120/P35/50 was almost the same as PCS120 raw material, suggesting that most
of the liquid SEDDS was adsorbed into mesopores and deep into the channels of pores
of the calcium silicates. The liquid SEDDS might have also partially spread on the
surface of PCS120. The results are consistent with previous report (76) that has found
the adsorption of oily liquid into the pores and spread on the surface of magnesium
aluminometasilicate (Neusilin® US2). Furthermore, no drug crystal was observed on
the surface of PCS120. Figure 7.3 shows the DSC thermograms of drug powders, drug-
loaded PCS120/P35/50 and physical mixtures of drug and PCS120. The physical
mixtures were prepared by simply mixing the drug and PCS120. Pure drug powders
showed a sharp endothermic peak at about 174.3, 143.5, 175.9 and 166.4 C for NDP,
FDP, MDP and ITZ, respectively, corresponding to their melting points and indicating
their crystalline nature (Figure 7.3). The melting peak was observed with a reduced
intensity in the physical mixtures of different drugs and PCS. However, the melting
peak of the drugs was absent in all of the PCS120/P35/50 formulations. It is likely that
the drugs might be in an amorphous state in the solid SEDDS formulations. The PXRD
patterns revealed that the drugs had sharp distinct characteristic peaks at 2 theta
diffraction angles of 11.9°, 19.6° and 24.1° for NDP, 10.2°, 16.3° and 23.2° for FDP,
10.0°, 21.3° and 22.9° for MDP, and 7.3°, 17.4°, 17.9°, 20.3° and 23.4° for ITZ,
showing a typical crystalline pattern (Figure 7.4). PCS showed no sharp peak. All of
the major characteristic crystalline peaks for the drugs and PCS120 were observed in
their physical mixtures. The PCS120/P35/50 formulations containing different drugs
showed no peak at diffraction angles, indicating an amorphous nature. From the DSC
and PXRD results, all drugs were present in an amorphous state in the PCS120/P35/50
formulations.
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Table 7.1 Emulsion droplet size of SEDDS and solid SEDDS loading with different
drugs, diluted in water or SGF (n=3).
Formulation Size±S.D. (Polydispersity index)
Water SGF
SEDDS (with no drug) 129.5 ±0.4 nm (0.395) 114.5±0.0 nm (0.204)
NDP-loaded SEDDS 132.9±0.5 nm (0.183) 132.3±0.4 nm (0.178)
NDP-FS200/P35/50 132.2±0.1 nm (0.158) 149.2±0.6 nm (0.124)
NDP-PSD300/P35/50 132.9±0.1 nm (0.143) 130.4±0.1 nm (0.132)
NDP-PCS120/P35/50 131.9±0.1 nm (0.123) 135.4±0.5 nm (0.132)
FDP-loaded SEDDS 155.2±10.5 nm (0.227) 145.1±17.5 nm (0.207)
FDP-FS200/P35/50 112.9±0.1 nm (0.199) 140.2±0.1 nm (0.224)
FDP-PSD300/P35/50 130.9±0.1 nm (0.213) 128.4±0.1 nm (0.140)
FDP-PCS120/P35/50 126.8±0.1 nm (0.133) 128.1±0.2 nm (0.210)
MDP-loaded SEDDS 142.4±21.5 nm (0.234) 148.3±16.6 nm (0.241)
MDP-FS200/P35/50 128.2±0.2 nm (0.131) 134.2±0.5 nm (0.164)
MDP-PSD300/P35/50 132.6±0.1 nm (0.166) 129.4±0.1 nm (0.213)
MDP-PCS120/P35/50 125.9±0.1 nm (0.134) 125.4±0.5 nm (0.192)
ITZ-loaded SEDDS 139.4±11.2 nm (0.132) 138.1±15.6 nm (0.232)
ITZ-FS200/P35/50 128.2±0.1 nm (0.118) 133.2±0.6 nm (0.181)
ITZ-PSD300/P35/50 122.5±0.1 nm (0.123) 120.4±0.1 nm (0.112)
ITZ-PCS120/P35/50 129.9±0.1 nm (0.100) 129.4±0.5 nm (0.202)
Transformation from crystalline state to amorphous state favors the faster
dissolution of drug there by improved solubility and dissolution rate as later contains
high internal energy and improved thermodynamic properties compared to pure
crystalline drug. Similar results were reported by Kang et al. (146) that flurbiprofen is
in an amorphous state in the solid self-nonoemulsifying drug delivery system using
different solid carriers.
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Figure 7.2 SEM micrographs of PCS120/P35/50 loaded with different drugs
(magnification of 1000X (left) and 5000X (right)).
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NDP-PCS120/P35/50
FDP-PCS120/P35/50
MDP-PCS120/P35/50
ITZ-PCS120/P35/50
PCS120
NDP
NDP/PCS120_PM
FDP/PCS120_PM
FDP
MDP/PCS120_PM
MDP
ITZ/PCS120_PM ITZ
Figure 7.3 DSC thermograms of drug powders, drug-loaded PCS120/P35 formulations
and physical mixtures (PM) of drug and PCS120 (1:5).
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NDP-PCS120/P35/50
FDP-PCS120/P35/50
MDP-PCS120/P35/50
ITZ-PCS120/P35/50
PCS120
NDP
NDP/PCS120_PM
FDP/PCS120_PM
FDP
MDP/PCS120_PM
MDP
ITZ/PCS120_PM
ITZ
Figure 7.4 Powder X-ray diffractrograms of drug powders, drug-loaded PCS120/P35
formulations and physical mixtures (PM) of drug and PCS120 (1:5)
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7.3.2 In vitro drug dissolution
The drug dissolution profiles of drug powders (NDP, FDP, MDP and ITZ),
SEDDS and PCS120/P35/50 formulations, in SGF, are shown in Figure 7.5. Only small
or negligible amounts of the drugs were dissolved within 120 minutes. The higher drug
dissolution was obtained from the SEDDS formulations. The maximum drug dissolved,
at 60 min, from each formulation was found to be 99%, 74%, 52% and 33% for SEDDS
loaded with NDP, FDP, MDP and ITZ, respectively. It was found that the dissolution
of drug decreased when the lipophilicity (LogP) of drugs was increased. The inverse
dependency (with a good linear relationship) between the drug dissolution and
lipophilicity of drugs was clearly seen (Figure 7.6a). The results suggested that the
lipohilicity of drug played an important role in drug dissolution. Sawant et al. (147)
reported that the drug dissolution from hydroethanolic formulations depends on the
lipophilicity (LogP) of drugs, that is, the dissolution of drug with lower lipohilicity
(lidocaine hydrochloride; LogP ≤ 0) is faster and demonstrates a burst effect, compared
to that with higher lipohilicity (lidocaine; LogP= 2.6).
The dissolution profiles of solid SEDDS formulations loaded with different
drugs were shown in Figure 7.5b. The drug dissolution from solid SEDDS formulations
has higher drug dissolution than drug powders, ensuring that the solid SEDDS
preserved the improvement of drug dissolution of liquid SEDDS. More than 80% of
drugs were dissolved at the end of study (120 minutes). Among these formulations,
NDP-PCS120/P35/50 showed the fastest dissolution rate, almost 100% of NDP
dissolved within 10 minutes. It is apparent from the dissolution study that the drug
dissolution was faster for the solid SEDDS, compared to drug powders and drug-loaded
SEDDS, which may be due to the increased effective surface area and alteration in the
crystalline properties of the drugs. Moreover, the solid SEDDS formulations resulted
in spontaneous formation of nanoemulsions with a small droplet size permitting faster
drug dissolution into aqueous phase, compared to drug powders. It also seen that the
effect of lipophilicity was reduced by solid SEDDS formulation (Figure 7.6b) as the
slope of the plot between LogP and % drug dissolved at 60 min was decreased. This
result may due to increase of surface area exposure of solid SEDDS.
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Figure 7.5 Drug dissolution profiles of (a) drug powders and SEDDS formulations,
and (b) solid SEDDS formulations loaded with different drugs, in SGF (n=3).
NDP-loaded SEDDS MDP-SEDDS
NDP FDP
MDP ITZ
FDP-loaded SEDDS MDP-loaded SEDDS
ITZ-loaded SEDDS
NDP-PCS/PCS120/P35/50
FDP-PCS/PCS120/P35/50
MDP-PCS/PCS120/P35/50
ITZ-PCS/PCS120/P35/50
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0
20
40
60
80
100
120
0 1 2 3 4 5 6% d
rug
diss
olve
d at
60
min
LogP
y = -6.6087x + 120.54R² = 0.9973
0
20
40
60
80
100
120
0 1 2 3 4 5 6
% D
rug
diss
olve
d at
60
min
LogP
y = -18.725x+149.09 R2 = 0.9029
(a)
(b)
Figure 7.6 Relationship between lipophilicity (LogP) and % drug dissolved at 60 min
of (a) SEDDS formulations and (b) solid SEDDS formulations.
7.4. Conclusion
In this study, solid SEDDS formulation were prepared using different drugs
by adsorption of drug-loaded SEDDS onto PCS120 at the concentration of 50%. The
solid characterization by SEM, DSC and PXRD revealed the absence of drug
crystallinity in the formulations. Solid SEDDS also demonstrated excellent
spontaneous emulsification properties similar to SEDDS. The other poorly water-
soluble drugs i.e., FDP, MDP and ITZ could be applied in SEDDS and solid SEDDS
formulations. The linear relationships between drug dissolution and lipophilicity were
clearly observed. Moreover, PCS120 had significant and positive effects in drug
dissolution in the solid SEDDS.
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CHAPTER 8
Summary and general conclusion
Nearly 40% of new drug candidates are poorly water-soluble drug, which
leads to poor oral bioavailability, high variable absorption and lack of dose
proportionality. The absorption rate of poorly water-soluble drug from the GI lumen is
governed by dissolution step. The beneficial effects of food or oil on hydrophobic drug
were reported and several successful oral pharmaceutical products have been marketed
as lipid-based formulation. Consequently, there is considerable interest in the potential
of lipid-based formulation. The oral lipid-based formulations can also enhance drug
absorption by several auxiliary mechanisms including inhibition of P-glycoprotein-
mediated drug efflux and pre-absorptive metabolism by gut membrane-bound
cytochrome enzymes, promotion of lymphatic transport. In this reason, the drug will be
delivered directly to the systemic circulation while avoiding hepatic first-pass
metabolism (11).
SEDDS, which is isotropic mixture of oil, surfactant, solvent and co-
solvent/co-surfactant, can be used for the design of lipid-based formulations in order to
improve the oral absorption of highly lipophilic compounds. SEDDS rapidly form a
fine oil-in-water emulsion (a droplet size between 100 and 300 nm) when exposed to
aqueous media under conditions of gentle agitation or digestive motility that would be
encountered in the GI tract. The selected techniques for improving the dissolution and
absorption were based on approaches, HLB value and ternary phase diagram. The
impacts of HLB and molecular structure of surfactants on the formation of SEDDS
were investigated (Chapter 3). After screening of various oils and surfactants, NDP-
loaded SEDDS was formulated with CCG as oil, and polysorbate/sorbitan monoester
or polyoxyls/sorbitan monoester as mixed surfactant. Droplet size of emulsions
obtained after diluting SEDDS containing polysorbate/sorbitan monoester in aqueous
medium was independent of the HLB of a mixed surfactant.
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The use of polyoxyls/sorbitan monoester blends gave nano-sized emulsions
at higher HLB. Structure of surfactant is found to influence the emulsion droplet size.
Solid SEDDS was then prepared by adsorbing NDP-loaded SEDDS comprising
P40/sorbitan monooleate onto FS200 or FSR as inert solid carrier. Solid SEDDS
formulations using higher amount (30-50% w/w) of FS200 exhibited good flow
properties with smooth surface and preserved the self-emulsifying properties of liquid
SEDDS. Although the HLB system is not absolute in prediction of the formulation
behavior, it is a very good starting point for achieving emulsification.
SEDDS was also prepared by using ternary phase diagram, and their
spontaneous emulsifying property as well as dissolution of NDP were investigated
(Chapter 4). The results showed that the composition of the SEDDS was a great
importance for the spontaneous emulsification. Based on ternary phase diagram, the
region giving the SEDDS with emulsion droplet size of less than 300 nm after diluting
in aqueous medium was selected for further formulation. The SAXS curves of the
developed formulations showed no sharp peak after dilution at different percentages of
water, suggesting non-ordered structure. The system was found to be robust in different
dilution volumes. In vitro dissolution study showed remarkable increase in dissolution
of NDP from SEDDS formulations compared to NDP powders.
The solid carriers, e.g., FS, PSD and PCS at the concentration of 20-50%
were incorporated in the formulations to select the suitable formulations (Chapter 5).
Drug dissolution was found to depend on the type of solid carrier and pore size at the
SEDDS/solid carrier interface. The results revealed that the formulation NDP-
PCS120/P35/50 provided a free-flowing behavior and highest drug dissolution. The
solid carriers (particularly PCS120) had significant and positive effect in drug
dissolution; the MDT of solid SEDDS containing PCS120 was considerably improved.
Solid SEDDS also provided a good stability after storage for 6 months in accelerated
and long-term conditions. The bioavailability resulted showed the increased values of
Cmax and AUC for solid SEDDS formulations, when tested in both fasted and fed rats
(Chapter 6). Furthermore, comparing the AUC in fasted and fed rats, NDP powder
exhibited a significant food effect. The food effect of NDP in fed compared to fasted
state was reduced by using SEDDS and solid SEDDS.
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The selected SEDDS formulations were tested if they could be as universal
SEDDS formulations by applying other poorly water-soluble drugs with different
lipophilicity (LogP), NDP, FDP, MDP and ITZ in the selected formulations (Chapter
7). It found that drug dissolution from SEDDS was different, depending on lipophilicity
of drug, i.e., 98.6, 74.3, 52.5% and 33% for NDP (LogP 2.50), FDP (LogP 4.46), MDP
(LogP 5.46) and, ITZ (LogP 5.66), respectively. The results suggested the inverse
linearly relationship between drug dissolution from SEDDS and LogP. The inverse
dependency between the drug dissolution and lipophilicity was observed; the decrease
in amount of drug dissolved was probably caused by an increased lipophilicity of the
drugs.
In this research, the SEDDS formulations were developed based on HLB
and the construction of ternary phase diagram. The solid carriers were used to produce
the solid SEDDS with free-flowing behavior. The enhancement of drug dissolution and
absorption was achieved by selected formulations of SEDDS and solid SEDDS.
Moreover, the other drugs ,i.e., FDP, MDP and ITZ were successfully applied in
SEDDS formulations.
Future direction of research
This study has developed the solid SEDDS using oil, surfactant, co-
surfactant and various types of solid carriers, which can increase dissolution and
absorption of NDP. The in vivo absorption study of solid SEDDS containing the other
drugs (e.g., MDP, FDP and ITZ) should be also studied.
The functional surface group of solid carriers and micro/mesoporous
materials could be applied to solid SEDDS for discussion improvement and decreased
the inactive gradients in the formulations.
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140. Nepal PR, Han H-K, Choi H-K. Preparation and in vitro–in vivo evaluation of
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141. Ueno K, Kawashima S, Uemoto K, Ikada T, Miyai K, Wada K, et al. Effect of
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142. Kawakami K, Yoshikawa T, Hayashi T, Nishihara Y, Masuda K. Microemulsion
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al. Formulate-ability of ten compounds with different physicochemical
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146. Kang JH, Oh DH, Oh YK, Yong CS, Choi HG. Effects of solid carriers on the
crystalline properties, dissolution and bioavailability of flurbiprofen in solid
self-nanoemulsifying drug delivery system (solid SNEDDS). Eur J Pharm
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147. Sawant PD, Luu D, Ye R, Buchta R. Drug release from hydroethanolic gels.
Effect of drug's lipophilicity (logP), polymer-drug interactions and solvent
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BIOGRAPHY
Name Mr. Yotsanan Weerapol
Date of birth 13 April 1985
Place of birth Sing Buri, Thailand
Nationality/Religion Thai/Buddism
Home address 28 M1 Angkeaw, Pothong, Angthong 14120 Thailand
Telephone number +66863690676
Email address [email protected]
Education
2008 (June)-2014 (December) Doctor of Philosophy (Pharmaceutical Technology) Silpakorn University, Thailand
2003 (June)-2007 (January) Bachelor of Pharmacy, Silpakorn University, Thailand
Publications
1. Sriamornsak P, Thirawong N, Weerapol Y, Nunthanid J, Sungthongjeen S.
Swelling and erosion of pectin matrix tablets and their impact on drug
release behavior. European Journal of Pharmaceutics and
Biopharmaceutics 2007; 67(1): 211-219.
2. Sriamornsak P, Nunthanid J, Luangtana-anan M, Weerapol Y,
Puttipipatkhachorn S. Alginate-based pellets prepared by
extrusion/spheronization: Effect of the amount and type of sodium alginate
and calcium salts. European Journal of Pharmaceutics and
Biopharmaceutics 2008; 69(1): 274-284.
3. Weerapol Y, Cheewatanakornkool K, Sriamornsak P. Impact of gastric pH and
dietary fiber on calcium availability of various calcium salts. Silpakorn
University Science and Technology Journal 2010; 4(1): 17-25.
4. Sriamornsak P, Kontong S, Weerapol Y, Nunthanid J, Sungthongjeen S,
Limmatvapirat S. Manufacture of ternary solid dispersions composed of
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nifedipine, Eudragit® E and adsorbent. Advanced Materials Research
2011; 317-319:185-188.
5. Weerapol Y, Kumpugdee-Vollrath M, Sriamornsak P. Behaviour of lipid-based
formulations containing nifedipine in aqueous media as observed by small
angle X-ray scattering. Advanced Materials Research 2013; 747:139-142.
6. Nernplod T, Weerapol Y, Sriamornsak P. Preparation of solid self-emulsifying
drug delivery system of manidipine hydrochloride. Advanced Materials
Research 2013; 747: 143-146.
7. Weerapol Y, Limmatvapirat S, Nunthanid J, Sriamornsak P, Self-
nanoemulsifying drug delivery system of nifedipine: Impact of hydrophilic-
lipophilic balance and molecular structure of mixed surfactants. AAPS
PharmSciTech 2014;15 (2):456-64.
8. Kumpugdee-Vollrath M, Weerapol Y, Schrader K, Sriamornsak P.
Investigation of nanoscale structure of self-emulsifying drug delivery
system containing poorly water-soluble model drug. Advanced Materials
Research 2014; 970: 272-278.
9. Weerapol Y, Limmatvapirat S, Kumpugdee-Vollrath M, Jansakul C,
Sriamornsak P. Spontaneous emulsification of nifedipine-loaded self-
nanoemulsifying drug delivery system. AAPS PharmSciTech 2014;
accepted 31 October 2014.
10. Weerapol Y, Limmatvapirat S, Sriamornsak P. Fabrication of spontaneous
emulsifying powders for improved dissolution of poorly water-soluble
drugs. Powder Technology 2015; 271: 100-108.
Patents/Patent applications
1. Sriamornsak P, Weerapol Y. Process of drying for incubated broth using porous
adsorbent. Thai patent application 0901005886, 30 December 2009.
2. Sriamornsak P, Weerapol Y. Composition of products in powders and solid
dosage forms containing incubated broth for plant pathogen control. Thai
patent application 1001000228, 15 February 2010.
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Presentations
1. Sriamornsak P, Charrennit P, Weerapol Y, Churasri Y, Loudlerdwilai S,
Ungphaiboon S. Effect of sterilization treatment on the viscosity of selected
polymer solutions. The 4th Thailand Pharmacy Congress, Bangkok, 6-7
December 2007.
2. Weerapol Y, Cheewatanakornkool K, Sriamornsak P. Effect of type of calcium
and dietary fiber on calcium availability of calcium supplement tablets. The
Thai Journal of Pharmaceutical Sciences 2008; 32(supp): 61.
3. Weerapol Y, Cheewatanakornkool K, Sriamornsak P. Effect of gastric pH on
calcium availability of various calcium salts. The 3rd Asian Pacific
Regional International Society for the Study of Xenobiotics (ISSX)
Meeting, Bangkok, 10-12 May 2009.
4. Weerapol Y, Sriamornsak P. Characterization of product derived from Bacillus
subtilis for plant disease control. The 5th Thailand Pharmacy Congress,
Bangkok, 27-28 December 2009.
5. Weerapol Y, Sriamornsak P. Development of solid dosage forms containing
bacteria (Bacillus subtilis) for plant pathogen control. Proceedings of the
3rd Silpakorn University Research Fair 2010; 3: P124-P128. [Nakhon
Pathom, 28-29 January 2010]
6. Sriamornsak P, Burapapadh K, Weerapol Y, Cheewatanakornkool K.
Improvement of dissolution characteristics of itraconazole, a poorly water-
soluble drug, by various techniques. Special Lecture at Gifu
Pharmaceutical University, supported by Pharmaceutical Society of
Japan, Gifu, Japan. 21 July 2010.
7. Sriamornsak P, Thirawong N, Burapapadh K, Weerapol Y,
Cheewatanakornkool K. Biopolymer as nanocarriers for oral drug delivery.
NRCT-CPS Conference V. Drug Discovery: Development of Drug
Design-based Pharmaceuticals, Rayong, 3-5 September 2010.
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