Bioequivalence studies of drugs prescribed mainly for women

The basic components of pharmacokinetics are absorption, distribution, metabolism, and excretion. During pregnancy there may be changes in one or many of these components. Early drug studies did not include a representative proportion of women, however, researchers as well as regulators agree that studies on the sex differences in the disposition of drugs are important, but at what stage in the clinical trial process? Except for drugs used only in women, such as those for estrogen-dependent breast cancer, caution prevails and the differences are usually studied at phase 3. Studies in pregnant women are much rarer but some do get done, e.g., with antivirals and antimalarials, where the positive risk-benefit of these agents is the likelihood that fetal transfer of these drugs might help protect the fetus. Women are being included in pharmacokinetic studies for new drug applications in accordance with the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH), U.S. Food and Drug Administration (FDA), and Health Canada (HC) guidances. A new look at bioequivalence studies, to compare results in men and women, would help determine if interactions of formulation and gender are a problem.