Scientific Tracks Abstracts: J Bioequiv Availab
R egulatory approval processes for bioequivalent topical products often require clinical efficacy trials. The U.S. Food, Drug and Cosmetic Act, and associated regulations, allow for utilization of alternative in vitro and in vivo methods for assessing bioequivalence of topical dosage forms. Yet to date, the vasoconstrictor assay for topical glucocorticoids is the only approved surrogate method, despite the fact that there are multiple definitive and discriminating alternative methods currently available. For example, a substantial body of data demonstrates that in vitro percutaneous absorption in excised human skin on Franz cells shows excellent correlation with absorption in living man. When in vitro studies are conducted under parameters that match in vivo conditions, the average IVIV ratio is very close to one (0.96) with a range 0.58 ? 1.28. A critical component of IVIV correlation is studying the matched body site. This correlation has been consistently demonstrated in numerous well matched in vitro ? in vivo studies, where test and reference formulations were found to be equally bioavailable in vitro , and validated when subsequent clinical evaluation found those products to be bioequivalent. Correlation of bioequivalence has been shown both, with quantitative in vivo pharmacokinetics of total absorption, and with qualitative pharmacodynamic clinical endpoints like the vasoconstrictor score and therapeutic efficacy. For regulatory approval, the in vitro excised skin data need not be relied upon in isolation to determine bioequivalence, but should be considered as an informative supplement to results from other methods currently available, as part of a hierarchical approach to determining bioequivalence.