Fitting Pharmacodynamic Data to the Emax Model to Assess the Inherent Potency of Topical Corticosteroids.

ABSTRACT

The widespread use of topical corticosteroids (TCs) in dermatotherapy requires a consideration of their potency and benefit/risk ratios. Although there are a variety of topical corticosteroid products (TCPs) available on the market and their potencies are ranked using different classification systems, to our knowledge, no classification system to rank the inherent potencies of TC active pharmaceutical ingredients (APIs) currently exists. Most of the published classification systems for TCPs are based on randomized clinical comparative studies and/or vasoconstrictor assay (VCA) data. The objective was to apply the US FDA's VCA to classify the inherent potencies of several TCs using standardized doses to make appropriate comparisons of the relevant APIs in solutions of the same molar concentrations. Six TC APIs were assessed for their relative potencies using healthy human participants. The Emax model was used to fit skin blanching data following application of the respective TCs, and the parameters, Emax and ED50, were derived. Emax values were used as the metric to assess potency. Statistical analyses of the data revealed that the inherent potencies of fluticasone propionate, mometasone furoate, and hydrocortisone butyrate were similar. However, there was no significant difference between hydrocortisone butyrate and clobetasol propionate, while there was a significant difference between clobetasol propionate, fluticasone propionate, and mometasone furoate. Hence, the potency of hydrocortisone butyrate appears to overlap two potency classes. Furthermore, the potencies of betamethasone valerate and methylprednisolone aceponate were similar but lower than those of all of the other APIs. The application of the VCA to classify inherent potency provides a reliable method to establish a classification system for TCs. Inherent potency assessment of TCs provides information that will be useful when choosing an appropriate TC for the development of a TCP for a specific clinical indication.