The vasoconstrictor assay in bioequivalence testing: practical concerns and recent developments.

The vasoconstrictor assay, when properly performed, is a highly reliable method to determine bioequivalence of generic formulations. Recent research has resolved some of the remaining questions concerning the practical application of the assay. Significant vehicle-related differences have been observed between the potency of different, supposedly equivalent formulations now on the market. Large differences in concentrations of the active agent in similar vehicles usually have not resulted in corresponding differences in vasoconstrictor assay results. Finally, the time course of drug effects may differ among highly potent and less potent corticosteroids. In general, the higher the potency of the topical corticosteroid, the earlier the maximal effect is observed. This finding suggests that short application of highly potent agents might minimize systemic absorption without sacrificing efficacy.