Early Stage Clinical

Paul Lehman, QPS' Vice President and Head of Dermal and Transdermal Research, Publishes a Comparison of Methods for Assessing Topical Bioavailability - August, 2014

Currently, establishing the bioequivalence (BE) of topical drug products is not a simple process: in contrast to oral medications, costly and time-consuming clinical trials are required for most topicals. US regulations provide for alternative methods (i.e. surrogates for clinical trials) to be used to establish BE. The Food and Drug Administration (FDA) prefers pharmacodynamics effect studies, but in vivo animal studies as well as in vitro studies may also be acceptable. Although only one surrogate test for topical products (the “skin blanching” or “vasoconstrictor assay” for glucocorticoids) is currently approved, FDA activity over the past twenty-five years - through sponsored scientific meetings and research, as well as in-house research and initiatives - has generated several alternative test methods for topical products.

In the study described, Lehman and co-author Thomas Franz compared the sensitivity of a pharmacokinetic assay, the in vitro permeation test (IVPT), with that of a pharmacodynamic assay, the human skin blanching or vasoconstrictor (VC) assay, in assessing the relative bioavailability of topical clobetasol propionate products. Interestingly, IVPT was found to be substantially more sensitive and less variable than the VC assay for assessing clobetasol bioavailability.

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