Progress in methodologies for evaluating bioequivalence of topical formulations.

Assessment of bioequivalence of topical dermatological formulations is a challenge. Currently, comparative clinical studies are used to establish bioequivalence for most formulations (except corticosteroids). This article reviews different in vivo methodologies for determining bioequivalence, and the progress made in this area. Dermatopharmacokinetics is the term used to describe the pharmacokinetics of topically applied drugs in the stratum corneum. A tape stripping procedure used in dermatopharmacokinetic methodology measures the drug concentration in stratum corneum at the site of application. Various studies have shown dermatopharmacokinetics to be a reliable and reproducible method for determining bioequivalence, and have indicated that it is applicable for all topical dermatological drug products. However, confidence in this methodology needs to be established, particularly regarding its relevance to clinical drug efficacy.