BE studies- Part 3 : Statistical Phase, Special Situations, Guidelines

Dr. Ammar RazaClinician, Clinical Affairs Manager, Medical Advisor

Introduction

Performance will never be identical– Two formulations– Two batches of the same formulation?– Two tablets within a batch?

Purpose of bioequivalence (BE)– Demonstrate that performance is not

“significantly” different– Same therapeutic effect– What constitutes a ‘significant’

difference?

Phases of BE studies

Clinical Phase– Screening– Selection – ICF &

Recruitment – Dosing – Sampling– Monitoring– AEs

Bioanalytical Phase

– Storage of Samples

– Method Devpt– Method Validation – Analysis of

samples – QC checks

Statistical Phase – Data analysis– Anova (SAS)– PK (WinNonlin)-

AUC, Cmax etc. – T/R ratio– 90% CI

Focus on

BE Studies: Scientific Basis

Two different formulations of a drug resulting in SIMILAR systemic

concentration-time profiles will always achieve similar concentration time

profiles at the site of efficacy or toxicity

Metrics for BE studies

Concentration vs. time profiles– Area under the curve (AUC)

Observable exposure AUC-t (zero to last detectable concn) Complete exposure AUCinf

– Maximal concentration (Cmax)– Time to Cmax (Tmax)

Statistical measures of BE metrics– Mean– Variance

Stat BE: comparing the means of two products

Overall extent

Both rate & extent

PK analysis: Approaches

BE or rate & extent of BA or exposure can be proven using– Compartmental approach - not preferred in BE – Non-compartmental approach

Based on calculation of AUC –body’s exposure Favored to prove BE- robustness Min of 15 samples- to calculate AUC

Non-compartmental approach

Determination of BE

Modern concept of BE is based on a survey of physicians carried out by Westlake in 70s - a 20% diff in dose b/n 2 formulations - no clinical significance for most drugs

– BE limits were set at 80 - 120%. Pl concn. dependent measures - Cmax or AUC are

not normally distributed– Are log normal, – BE limits became 80 - 125% (or ± 0.225 on natural log

scale)

Statistical Determination of BE

Past method– tested null hypothesis- no difference between means

Not adequate in 1980s

Current method– proves similarity between two products– BE- diff <20%

Avg rate & extent of BA of T within ±20% that of R

– Log transformed scale- limits of ratio b/n 0.8 and 1.25

The statistical procedure ..

‘two one-sided test’– introduced by Hauck

Method – defines error α- probability of concluding BE when in reality it is not true

– Usually fixed to a min- 5%– BE concluded if 90% CI of the ratio is within 80-125– Power of study (regulatory)=80%– 20% probability of not demonstrating BE even if they are

truly BE– No of sub: based on variability of metric that study must

pass on Cmax: most variable metrics

Sample size

Analysis of Variance

ANOVA– Most common technique of analysis and estimation

Lognormal distribution– Raw data must be log transformed– Comparison of means & variances of transformed data– Geometric mean (GM)– Results reported in original scale

Confidence Intervals (CI)

Inference from study to wider world Range of values within which we can have a

chosen confidence that the population value will be found

Study findings expressed in scale of original data measurement

Confidence Intervals (cont.)

Width of CI indication of (im) precision of sample estimates

Width partially dependent on:– Sample size– Variability of characteristic being

measured Between subjects Within subjects Measurement error Other error

Confidence Intervals cont.

Degree of confidence required– More confidence = wider interval

Width of equivalence limits represents allowable boundary for ratio (or difference) of means b/n products in comparison

In other words, width of CI dependent on:– Standard error (SE)

Standard deviation, sample size– Degree of confidence required

Statistical Analysis (Two One-sided Tests Procedure)

Statistical analysis of pharmacokinetic measures– Confidence intervals– Two one-sided tests

AUC and Cmax– 90% Confidence Intervals (CI) must fit between

80%-125%

Typical BEAssessment Criteria

90% confidence interval Ratio of geometric means Acceptance criteria: 80 – 125% Log transformed AUCT & Cmax

Statistical Approaches for BE

Average bioequivalence Population bioequivalence Individual bioequivalence

Average BE Conventional method Compares only population averages Does not compare products variances Does not assess subject x formulation interaction

Statistical Approaches for BE

Population and individual BE– Include comparisons of means and variances

Population BE– Assesses total variability of the measure in the

population

Individual BE– Assesses within subject variability– Assesses subject x formulation interaction

Statistical effects in model

Sequence effect Subject (SEQ) effect Formulation effect Period effect Carryover effect Residual

Statistical Analysis Bioequivalence criteria

– Two one-sided tests procedure Test (T) is not significantly less than reference Reference (R) is not significantly less than testSignificant difference is 20% ( = 0.05 significance

level)– T/R = 80/100 = 80%– R/T = 80% (all data expressed as T/R so this

becomes 100/80 = 125%)

Special Situations

Highly variable drugs Endogenous substances Parent/ metabolite issues Long half-life drugs

Highly Variable Drugs (HVDs)

Intrasubject variability (CV%) ≥30%– Significant first pass metab or to a poor or erratic

absorption process Sample size in BE studies is determined -by

BA parameter with highest variability– most cases, Cmax has higher variability than

AUC May not pass even when the reference

product is tested against itself

Factors Contributing to the Variability

Related to Formulation– Disintegration– Dissolution– Permeability

NON-related to Formulation

Absorption:– Rate of GI transit: Stomach to the colon– Transport through GI mucosa

Pancreatic or bile acid secretion

Drug metabolism– induction– inhibition– Liver blood flow

Excretion– Renal blood flow

HVDP

highly variable drug product (HVDP) - formulation of poor pharmaceutical quality - drug itself is not highly variable- big component of within formulation variability (WFV)

– cannot be detected in traditional 2-treatment, 2-period, 2-sequence cross-over design studies

– Replicate designs- facilitate their detection - within-subject variabilities of test & reference formulations can be estimated separately

When they are v. different - one of the formulations is a HVDP

Approaches

Evaluate bioequivalence at steady-state– Variability expected at steady-state is < that after single dose– Always true?– Can not be applied to all HVD/HVDP

Assessment of BE on the metabolite– When parent undetectable- metabolite is less variable– smaller sample size - BE studies for HVD if based on the

metabolite Add-on Individual BE- may help overcome existing problems ABE Average BE with scaling approach & widen CI

IBE Vs. ABE

Study periods are duplicated 4 vs. 2– Bad: duration & cost x 2– Good: may reduce pool size of volunteers - HVD

Has not found unanimous consensus in the scientific community – Remains under investigation– Subject of discussion in future

Wider CI

Major regulatory agencies have provisions - can accommodate effect of higher variability associated with Cmax on design of BE studies

EMEA -expanded limits (e.g., 75-133%) for Cmax in certain cases -NO safety or efficacy concerns

MCC, SA - allow for expanded limits for Cmax in certain cases

Example

2 BE studies on formulations of drugs A & B– same no. of sub in each study – GMR is the same in both– Two One-Sided Test - only difference b/n 2 studies is

magnitude of CV Drug A - low within-subject variability (ANOVACV

15%) - 90% CI falls comfortably within BE limits Drug B is highly variable - ANOVA-CV of 35%

– Study on drug B was underpowered- simple remedy - repeat study with a greater no. of sub

ProgesteroneThe Poster Drug for High Variability

A repeat measures study of Prometrium® 2x200 mg caps in 12 healthy PM females yielded:

Intrasubject CV for AUC of 61%

Intrasubject CV for Cmax of 98%

Generic company calculated that a 2 period crossover BE study - require dosing in 300 PM women to achieve adequate statistical power

Endogenous substances

Pose a major problem Baseline levels present

– Administration of drug can alter levels / feedback mechanism

– Oral admin- frequently produces only a negligible inc in baseline; wide variability

– Baseline should be measured throughout the day before dosing

Endogenous substances

Issues 100s or 1000s of vols to operate with net post-dose

values– Not acceptable from ethical or financial point of view

Lesser no of vols- post dose values without baseline subtraction

Steady state studies– preferred design when possible

Assay sensitivity issues

Predominating active metabolite

Parent/ metabolite issues Parent more variable Difficult to get detectable concn. (absent or

marginally present) Rate of abs- adequately evaluated only assaying

parent Measure metabolite

– Less of subs reqd– Easier to prove BE

Allopurinol, flutamide, terfenadine

Long half-life drugs

Crossover- adequate washout to avoid carryover – study lasts 4-6 m or more

Parallel design– More no. of sub (n=18 in crossover is stat equivalent to

~n=50 in parallel) Costly

Approaches: steady state or truncated AUC (stopping at 24 or 48 h)

– crossover -washout cannot be shortened, duration of study partially reduced

– Parallel design- markedly reduce duration of study

Topical application

Three classes Administered topically for absorption into sys

circulation e.g. patches– can use usual BE

Designed to exert topical activity only – absorption is negligible e.g. ointments, creams

– PD study or clinical efficacy study Designed to exert local activity – absorbed to a

certain extent only e.g. vaginal prep etc.– Considered individually

BE vs. Clinical Trial: Differences

Clinical Trial Multicentric Subjects: mostly

patients (except Ph I) Multiple doses Costly and time

consuming

BE study Single centre Subjects: Mostly

healthy vol; rarely pts. Single dose; sometimes

multiple dose Cheaper and require

less time

Focus on FDA Guidance

Two main guidances– General : “Bioavailability and Bioequivalence Studies for Orally

Administered Drug Products — General Considerations” http://www.fda.gov/cder/guidance/5356fnl.pdf

– “Food effect bioavailability studies and fed Bioequivalence studies”

http://www.fda.gov/cder/guidance/5194fnl.pdf– Drug specific guidances

Levothyroxine Potassium hydrochloride

– Biowaiver – Retention samples

Hatch-Waxman Amendments to FFD&C Act - 1984

Considered one of the most successful pieces of legislation ever passed

Created the generic drug industry

Increased availability of generics 1984 12% prescriptions were generic

2000 44% prescriptions were generic - yet only 8% of revenue for prescription drugs

Compromise legislation to benefit both brand and generic firms

Hatch-Waxman Amendments to FFD&C Act - 1984

Allowed generic firms to rely on findings of safety and efficacy of innovator drug after expiration of patents and exclusivities (do not have to repeat expensive clinical and pre-clinical trials)

Allowed patent extensions and exclusivities to innovator firms

Requirements for generic drugs

• Labeling

• Chemistry/Microbiology

• Bioequivalence

• Legal

Labeling

• “Same” as brand name labeling

• May delete portions of labeling protected by patent or exclusivity

• May differ in excipients, PK data and how supplied

Chemistry

• Components and composition• Manufacturing and controls• Batch formulation and records• Description of facilities• Specs and tests• Packaging• Stability

Manufacturing Compliance Programs

Purpose - To assure quality of marketed drug products

Mechanisms - Product Testing– Surveillance– Manufacturing/Testing plant inspections– Assess firm’s compliance with good

manufacturing processes

Guidance for CROs

Scope: Guidance to organizations involved in the conduct and analysis of in vivo bioequivalence (BE) studies

Note: BE studies should be performed in compliance with:

• General regulatory requirements• Good clinical practice (GCP)• Good laboratory practices (GLP)

Guidelines

Guideline provides information on:- organization and management- study protocols- clinical phase of a study- bio-analytical phase of a study- pharmacokinetic & statistical analysis - study report

Comparison of guidelines

Importance

Understanding the generic drug approval process and the issues surrounding BE is of paramount importance to both clinicians and scientists

Welage LS, Kirking DM, Ascione FJ, Gaither CA.J Am Pharm Assoc (Wash). 2001 Nov-Dec;41(6):856-67

Resources

Text book of pharmacokinetics

http://pharmacy.creighton.edu/pha443/pdf/pkin08.pdf

Summary

Planning is important– Study design, sample size, sampling schedule, incl & excl criteria

Conduct– Clinical & ethical: Protocol approval, selection of volunteers,

housing, dosing, sampling, AE recording and reporting, ambulatory samples,

– Bioanalytical assay method, equipment (HPLC / LC MS/MS), SOPs

– PK & Statistical Software (WinNonlin, SAS etc.)

Reporting– 3 Parts, CRFs, TMF, Chromatograms

Thank Youdr.razadiacare@rediffmail.com

Biowaiver

Recommended for a solid oral Test product that exhibit rapid (85% in 30 min) and similar in vitro dissolution under specified conditions to an approved Reference product when the following conditions are satisfied:– Products are pharmaceutical equivalent

– Drug substance is highly soluble and highly permeable and is not considered have a narrow therapeutic range

– Excipients used are not likely to effect drug absorption