Evaluation of a Scaling Approach for Highly Variable Drugs Sam H. Haidar, Ph.D., R.Ph. Office of Generic Drugs Advisory Committee for Pharmaceutical Sciences October 6, 2006
Outline Background Simulations-Based Research Project Results and Conclusion
Background ACPS Meeting, April 14, 2004: Discussion on Highly Variable Drugs Different approaches were considered, e.g., expansion of bioequivalence limits, and scaled average bioequivalence Committee favored scaled average bioequivalence over other approaches FDA working group was created; a research project to evaluate scaling was initiated ACPS = Advisory Committee for Pharmaceutical Science
Research Project Highly Variable Drugs (HVD) working group evaluated different scaling approaches and study designs to test. Outcome: Research project using: –Scaled average bioequivalence, based on within subject variability of reference* *
Objective Determine the impact of scaled average bioequivalence on the power (percent of studies passing) at different levels of within subject variability (CV%)
Methods Study design: 3-way crossover, e.g., R T R Sample sizes tested: 24 and 36 Within subject variability: 15% - 60% CV Geometric mean ratio: 1 – 1.7
Methods Statistical Analysis: Modified Hyslop model* Number of simulations: 1 million (10 6 )/test Percent of studies passing was determined using average bioequivalence (80-125% limits), and scaled average bioequivalence (limits determined as a function of reference within subject variability) Test performed under different conditions *Hyslop et al. Statist. Med. 2000; 19: Hyslop’s model was modified by Donald Schuirmann
Methods Variables tested: Impact of increasing within subject variability Use of point estimate constraint (80-125) σ w0 : 0.2 vs vs Sample size: 24 vs. 36
Results
Impact of Within Subject Variability 15% CV 30% CV 60% CV
Impact of Point Estimate Constraint Lower variability (30% CV) Higher variability (60% CV)
Impact of σ W0 σ W0 = 0.2 σ W0 = 0.25 σ W0 = 0.294
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Sample Size N = 24 N = 36
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Summary Partial replicate, 3-way crossover design appears to work well A point estimate constraint has little impact at lower variability (~30%); more significant effect at greater variability (~60%) A σ W0 = 0.25 demonstrates a good balance between a conservative approach, and a practical one
Conclusion Scaled ABE presents a reasonable option for evaluating BE of highly variable drugs Practical value, reduction in sample size: Decreasing cost and unnecessary human testing (without increase in patient risk) Use of point estimate constraint addresses concerns that products with large GMR differences may be judged bioequivalent
Acknowledgments Barbara Davit (Co-Chair) Lawrence Yu Donald Schuirmann Fairouz Makhlouf Dale Conner Mei-Ling Chen Devvrat Patel Lai Ming Lee Highly Variable Drugs Working Group:
Acknowledgments Robert Lionberger Qian Li Sarah Marston Other Contributors: