Application of E max model to assess the potency of topical corticosteroid products

Various potency classification listings for topical corticosteroid products (TCPs) have been based on clinical data and/or data using the US FDA’s vasoconstrictor assay (VCA). However, studies that used VCA data mainly used a single visual measurement and often the doses and dose durations were not determined in accordance with the VCA requirements. The objective was to compare the potencies of two TCPs using the Emax model to fit the blanching responses obtained from the VCA as described in a previous publication and to illustrate the influence of formulation on potency. The potencies of two marketed creams, Dermovate® containing clobetasol propionate (CP) and Elocon® containing mometasone furoate (MF) were assessed using healthy human subjects. In order to investigate the influence of formulation and associated vehicle properties, the TCPs were compared to their respective TCs from a previously published study wherein the inherent potencies of those TCs were assessed using a validated VCA method. Whereas the inherent potency of MF (Emax = -94.45 ± 0.21) was found to be greater than CP (Emax = -58.80 ± 15.65), when formulated as creams, the TCP containing CP had a higher potency (Emax = -86.15 ± 0.17) than that containing MF (Emax = -42.61 ± 26.04). This reversal of potency may be attributed to the effect of formulation factors. The comparison of the potencies of TCPs with inherent potencies of their corresponding TCs confirmed the influence of formulation parameters on the potency of those products.