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Centers for Education & Research on Therapeutics™
Interaksi obat
Dr. Risdawati Djohan, M.Kes.,Apt
Blok Emergency/ TA 2014-2015
Centers for Education & Research on Therapeutics™
a
Blok Emergency/ TA 2014-2015
Centers for Education & Research on Therapeutics™
a
Blok Emergency/ TA 2014-2015
Interaksi yang menguntungkan:
penisilin dengan probenesid, probenesid
menghambat sekresi penisilin di tubuli ginjal
kadar penisilin dalam plasma
efektivitasnya dalam
terapi gonore
kombinasi obat antihipertensi meningkatkan efektivitas
dan mengurangi efek
samping
kombinasi obat antiasma meningkatkan efektivitas
kombinasi obat antidiabetik meningkatkan
efektivitas;
kombinasi antibiotik antipseudomonas meningkatkan efektivitas
kombinasi obat antikanker juga meningkatkan
efektivitas
Centers for Education & Research on Therapeutics™
a
Blok Emergency/ TA 2014-2015
kombinasi antibiotik
antipseudomonas
meningkatkan efektivitas
kombinasi obat antikanker juga meningkatkan
efektivitas
kombinasi obat anti-HIV memperlambat timbulnya
resistensi virus terhadap
obat
kombinasi obat antihepatitis meningkatkan efektivitas
kombinasi obat untuk H. pylori meningkatkan efektivitas
kombinasi antibiotik betalaktam
dengan penghambat penghambat
betalaktamase
meningkatkan efektivitas
kombinasi sulfametoksazol dengan
trimetoprim
meningkatkan efektivitas
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Faktor yang memudahkan terjadinya
interaksi obat: polifarmasi
Survei (1977)
– insidens efek samping pada pasien dirawat di rumah sakit karena polifarmasi :
3,5% pada pemberian 0-5 macam obat
54% pada pemberian 16-20 macam obat
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Interaksi obat penting secara klinik, jika
meningkatkan toksisitas dan/atau
mengurangi efektivitas terutama jika menyangkut obat dengan batas keamanan yang sempit (indeks terapi yang rendah atau slope log DEC yang curam) misalnya:
glikosida jantung
antikoagulan
obat-obat sitostatik.
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Dosis terapi median atau dosis efektif median (=ED50): Dosis yang menimbulkan efek terapi pada 50% individu disebut
Dosis letal median (=LD50): dosis yang menimbulkan kematian pada 50% individu, atau menimbulkan keracunan pada 50% individu (dosis toksik 50% = TD50)
Dalam studi farmakodinamik di laboratorium, indeks terapi suatu obat dinyatakan dalam rasio berikut:
Batas Keamanan
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Centers for Education & Research on Therapeutics™
Monahan BP et al. JAMA 1990;264(21):2788–2790.
Case 1: Torsades de Pointes
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Monahan BP et al. JAMA 1990;264(21):2788–2790.
Ventricular Arrhythmia (Torsades de Pointes) with Terfenadine Use
39-year-old female Rx with terfenadine 60 mg bid and cefaclor 250 mg tid 10 d
Self-medicated with ketoconazole 200 mg bid for vaginal candidiasis
2-day Hx of intermittent syncope
Palpitations, syncope, torsades de pointes (QTc 655 msec)
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Monahan BP et al. JAMA 1990;264(21):2788–2790.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Day of Administration
Terfenadine
Cefaclor
Ketoconazole
Medroxyprogesterone
Symptomatic
H
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Adapted from: Sinoway L, Li J. J Appl Physiol 2005;99:5–22.
Case 2: Rhabdomyolysis
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Kahri J et al. Rhabdomyolysis in a patient receiving atorvastatin and fluconazole. Eur J Clin
Pharmacol 2005;60:905–907.
Rhabdomyolysis:Atorvastatin & Fluconazole
76-year-old male with Hx of chronic atrial fibrillation and aortic stenosis
Initial prescription medications:
– Bisoprolol
– Digoxin
– Warfarin
– Doxicycline
– Fucidic acid
– Prednisolone
– Esomeprazole
– Pravastatin
– Fluconazole
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Kahri J et al. Eur J Clin Pharmacol 2005;60:905–907
Rhabdomyolysis in Association with Atorvastatin and Fluconazole Use
Pravastatin dosage increased from 40mg to 80mg/day
Pravastatin changed to Atorvastatin 40mg
After 7 days – Extreme fatigue
After 3 weeks – Hospitalized for dyspnea
– Creatinine 1.36
– CK 910 I.U.
Dx: Renal Failure and DEATH
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Weeks
Fluconazole
Pravastatin 80mg
Pravastatin 40 mg
Atorvastatin
Fatigue
Dyspnea & CK 910
Death
Fatal Rhabdomyolysis
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Insidens interaksi obat sulit diperkirakan, k/
1.dokumentasi masih sangat kurang
2. seringkali lolos dari pengamatan dokter (k/ pemahaman
mekanisme dan kemungkinan terjadinya interaksi obat
kurang baik)
interaksi obat berupa peningkatan toksisitas reaksi idiosinkrasi
interaksi obat berupa penurunan efektivitas diduga akibat
bertambahnya keparahan penyakit
terlalu banyak obat yang saling berinteraksi sehingga sulit untuk
diingat
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
3. kejadian atau keparahan interaksi dipengaruhi oleh
variasi individual:
pasien lanjut usia
penyakit parah
kapasitas metabolisme
polimorfisme genetik
Penyakit tertentu:
gagal ginjal a/ penyakit hati yang kronik
penyakit jantung kongestif
faktor-faktor lain
dosis besar
obat ditelan bersama-sama
penggunaan obat bebas/suplemen/ herbal, merokok, dll.
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Istilah
Hiperreaktif efek dihasilkan pada dosis rendah sekali
Hiporeaktif efek dihasilkan pada dosis dosis tinggi
sekali
Hipersensitif efek yang berhubungan dengan alergi
obat.
Supersensitif keadaan hiperreaktif akibat denervasi atau
akibat pemberian kronik suatu bloker reseptor yang
merupakan denervasi farmakologik.
Toleransi keadaan hiporeaktif akibat pajanan obat
bersangkutan sebelumnya.
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Istilah
Takifilaksis atau toleransi akut toleransi yang terjadi
dengan cepat setelah pemberian hanya beberapa dosis
obat
Resisten Jika toleransi timbul akibat pembentukan
antibodi terhadap obat, misalnya terhadap insulin.
Idiosinkrasi istilah yang digunakan untuk efek obat
yang aneh (bizzare), ringan maupun berat, tidak
tergantung dari besarnya dosis, dan sangat jarang terjadi.
– digunakan secara simpang siur istilah ini berubah menjadi
reaksi alergi obat atau akibat perbedaan genetik.
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
Mekanisme interaksi obat
1. interaksi farmaseutik atau inkompatibilitas (datap terjadi sebelumdan sesudah pemakaian obat)
2. interaksi farmakokinetik
– GI tract
– Plasma
– Liver
– Kidney
3. interaksi farmakodinamik
– Dpt terjadi di organ target
– Dpt terjadi sistemik ( misal tekanan darah)
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
INKOMPATIBILITAS
Terjadi di luar tubuh antara obat yang tidakdapat dicampur (inkompatibel)
interaksi langsung secara fisik a/kimiawi inaktivasi obat
pembentukan endapan
perubahan warna dan lain-lain
perubahan yang tidak terlihat
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
INKOMPATIBILITAS (lanjutan)
Interaksi farmaseutik yang penting (bagi seorang dokter):
interaksi antar obat suntik
interaksi antara obat suntik dengan cairan infus.
i-a antara obat dg obat a/ obat dg vehicle
Gentamisin + karbenisilin inaktivasi gentamisin
penisilin G + vitamin C inaktivasi penisilin G
amfoterisin B dlm lrt garam fisiologis a/lrt Ringer
amfoterisin B mengendap
fenitoin dalam larutan dekstrosa 5% fenitoin mengendap
Centers for Education & Research on Therapeutics™Blok Emergency/ TA 2014-2015
INTERAKSI FARMAKOKINETIK
Salah satu obat mempengaruhi
– Absorpsi
– Distribusi
– Metabolisme atau
– Ekskresi
dari obat kedua,
kadar plasma obat kedua atau
Akibatnya: toksisitas atau efektivitas obat
– Interaksi farmakokinetik tidak dapat diekstrapolasikan
ke obat
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They Can Occur in the GI Tract
Sucralfate, some milk products, antacids, and oral iron preparations
Omeprazole, lansoprazole,H2-antagonists
Didanosine (givenas a buffered tablet)
Cholestyramine
Block absorptionof quinolones, tetracycline, and azithromycin
Reduce absorptionof ketoconazole, delavirdine
Reduces ketoconazole absorption
Binds raloxifene,thyroid hormone, and digoxin
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Interactions in the Plasma
To date, most protein “bumping” interactions described are transient and lack clinical relevance
The transient increase in free drug is cleared more effectively
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Spectrum of Consequences of Drug Metabolism
Inactive products
Active metabolites
– Similar to parent drug
– More active than parent
– New action unlike parent
Toxic metabolites
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Microsomal Enzymes
Cytochrome P450
Flavin mono-oxygenase (FMO3)
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Phases of Drug Metabolism
Phase I
–Oxidation
–Reduction
–Hydrolysis
Phase II
–Conjugation
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Interactions Due to Drug Metabolism
Nearly always due to interaction with Phase I enzymes, rather than Phase II
Commonly due to cytochrome P450 enzymes which have highly variable activity and, in some cases, are genetically absent or over-expressed
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Phase I - Drug Oxidation
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Cytochrome P450 Nomenclature, e.g., for CYP2D6
CYP = cytochrome P450
2 = genetic family
D = genetic sub-family
6 = specific gene
NOTE: This nomenclature is genetically
based; it does not imply chemical specificity
Centers for Education & Research on Therapeutics™
Major Human CYP450 Isoforms
CYP2D6
CYP2E1
CYP3A4
CYP3A5
CYP3A6
CYP1A2
CYP2B6
CYP2C8
CYP2C9
CYP2C19
Centers for Education & Research on Therapeutics™
Shimada T et al. J Pharmacol Exp Ther 1994;270(1):414.
CYP3A
CYP2D6
CYP2C
CYP1A2CYP2E1
Relative Importance of
P450s in Drug Metabolism
CYP3A
CYP2C
CYP1A2
CYP2E1
?
CYP2D6
Relative Quantities
of P450s in Liver
CYP450 Activity in the Liver
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Nu
mb
er
of
Su
bje
cts
Increasing Metabolic Capacity
EMPM URM
Polymorphic Distribution
Multiple groups of traits in which each constitutes >1% of the population
91%
9%
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Cytochrome P450 3A
Responsible for metabolism of:
– Most calcium channel blockers
– Most benzodiazepines
– Most HIV protease inhibitors
– Most HMG-CoA-reductase inhibitors
– Most non-sedating antihistamines
– Cyclosporine
Present in GI tract and liver
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CYP3A Inhibitors
Ketoconazole
Itraconazole
Fluconazole
Cimetidine
Clarithromycin
Erythromycin
Troleandomycin
Grapefruit juice
NOT Azithromycin
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CYP3A Inducers
Carbamazepine
Rifampin
Rifabutin
Ritonavir
St. John’s Wort
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Aklillu E et al. J Pharmacol Exp Ther 1996;278(1):441– 446.
Cytochrome P450 2D6
Absent in 7-9% of Caucasians,
1–2% of non-Caucasians
Over-expressed in up to 30% of East Africans
Catalyzes primary metabolism of:
Codeine Many -blockers
Many tricyclic antidepressants
Inhibited by:
Fluoxetine Haloperidol
Paroxetine Quinidine
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Cytochrome P450 2C9
Absent in 1% of Caucasians and
African-Americans
Primary metabolism of:
• Most NSAIDs (including COX-2)
• S-warfarin (the active isomer)
• Phenytoin
Inhibited by fluconazole
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Cytochrome P450 2C19
Absent in 20–30% of Asians,
3–5% of Caucasians
Primary metabolism of:
Diazepam Phenytoin
Omeprazole Clopidogrel
Inhibited by:
Omeprazole Isoniazid
Ketoconazole
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Cytochrome P450 1A2
Induced by smoking tobacco
Catalyzes primary metabolism of:
Theophylline Imipramine
Propranolol Clozapine
Inhibited by:
Many fluoroquinolone antibiotics
Fluvoxamine Cimetidine
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Drug Transporters
P-Glycoprotein and others
Pump drugs out of cells, which alters distribution
Found in the following tissues:
– Gut
– Gonads
– Kidneys
– Biliary system
– Brain (blood-brain barrier)
– Placenta
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Marchietti S, et al. Clinical relevance of drug-drug and herb-drug interactions mediated by the
ABC transporter ABCB1 (MDR1, P-glycoprotein). The Oncologist 2007;12:927-41.
P - Glycoprotein Tissue Distribution
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Digoxin and PGP
Digoxin is a PGP substrate
Increased digoxin plasma conc.
when combined with:
Quinidine Verapamil
Talinolol Clarithromycin
Erythromycin Itraconazole
Ritonavir
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Liver disease
Renal disease
Cardiac disease ( hepatic blood flow)
Acute myocardial infarction?
Acute viral infection?
Hypothyroidism or hyperthyroidism?
Drug-Disease Interactions
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Dresser GK, et al. Clin Pharmacol Ther 2000;68(1):28–34.
Hours after Dose Hours after Dose
Grapefruit Juice and Felodipine
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Drug-Herbal Interactions
St. John’s Wort with:
–Indinavir
–Cyclosporine
–Digoxin
–Tacrolimus
–Possibly many others
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After St. John’s Wort
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