Simultaneous diffusion and metabolism of betamethasone 17-valerate in the living skin equivalent.

Simultaneous diffusion and metabolism of betamethasone 17-valerate was studied using betamethasone 17-valerate, betamethasone 21-valerate, and betamethasone as permeants. These corticosteroids were suspended in silicone adhesive and applied to an artificial living skin equivalent (LSE) for 72 h. When betamethasone was applied, no metabolites were detected in the receptor medium. Conversely, with betamethasone 21-valerate application, only betamethasone but no betamethasone 21-valerate was detected in the receptor medium indicating the metabolism of the latter by skin esterases. When tested with the theory for simultaneous diffusion and metabolism, the result is consistent with the enzyme rate constant in the LSE homogenate measured in a previous study. When betamethasone 17-valerate was applied to the LSE, more than half of the total amount of corticosteroids detected in the receptor medium was unchanged, consistent with the previously reported chemical (as opposed to enzymatic) degradation half-life of about 8 h. This result also indicated that very little metabolism of betamethasone 17-valerate occurred in the skin.