Sample size determination for bioequivalence assessment by means of confidence intervals

The statistical analysis of bioequivalence assessment has been consolidated in recent years through the work of Schuirmann [1987], Westlake [1988] and Hauschke et al. [1990], and this has been reflected in the CPMP Note for Guidance on Bioavailability and Bioequivalence and in the joint recommendations of the APV (International Association for Pharmaceutical Technology) and ZL (Central Laboratories of German Pharmacists) during a recent workshop in support of EC-Guidelines [Blume et al. 1990]. Since the decision procedure based on the inclusion of the shortest 90%-confidence interval in the bioequivalence range is the procedure of choice, and as this is equivalent to the two one-sided tests procedure, the sample size determination is based on the power of the latter. Following the approach of Phillips [1990] for the additive model, corresponding nomograms for the more relevant multiplicative model are given in this paper for various ratios of the expected means for test and reference and various coefficients of variation.