Percutaneous absorption of steroids: relative contributions of epidermal penetration and dermal clearance.

The permeation of triamcinolone, hydrocortisone, prednisolone, corticosterone, triamcinolone acetonide, testosterone, and betamethasone-17-valerate through excised human stratum corneum was quantified. The time course of permeation could be adequately described by a simple diffusion model suggesting that shunt transport may not be important. The disappearance of these steroids from aqueous solutions applied to human and rat dermis was also monitored. The concentrations of unbound steroid in the viable epidermis appeared to be mainly related to the blood perfusion rate in the dermis and, more importantly, to the lipophilicity of the steroid. The most lipophilic steroids penetrated the human epidermis at the fastest rates but are cleared from the viable epidermis at rates comparable to those found for more polar steroids.