Investigation on the Existence of Sex-By-Formulation Interaction in Bioequivalence Trials

The US Food and Drug Administration recommends that if a drug product is intended for use in both sexes, similar proportions should be recruited for bioequivalence (BE) studies. In contrast, in Europe, subjects can belong to either sex. Literature suggesting the existence of sex-by-formulation interaction (S × F) is limited to few studies. To investigate if S × F is observed, this work includes 120 BE studies. Differences larger than 20% between the ratio test/reference of women and men or statistically significant S × F occurred in 25 of 120 studies (20.8%). The prevalence is higher in small studies (36.00% vs. 16.8%). Large differences between the ratios of the sex groups are the tails of the distribution. Two studies were repeated, and the differences between the ratios of the sex groups disappeared. The 90% confidence intervals of S × F did not confirm any relevant S × F. There is no evidence to require studies in both sex groups, combined or separately.