Use of the Stratum Corneum Reservoir for the Prediction of Skin Penetration

A simple and quick method based on the transient diffusion theory for predicting the steady state rate of penetration of a drug after transdermal drug administration was proposed. The amount of drug entering the stratum corneum was determined by 20 strippings with an adhesive tape. From the profile of the amount of drug as a function of the number of strippings, the quantity of drug on the surface of stratum corneum was extrapolated. Based on the amounts of drug entering the stratum corneum during two time intervals $(t_1\;and\;t_2)$ within 1 hour after the application, the diffusion and partition coefficient were determined. Once the diffusion coefficient of the drug in the stratum corneum and the partition coefficient (stratum corneum/vehicle) were determined from the present approach, the steady-state flux of penetration across the stratum corneum was calculated. The steady-state rates of penetration of ascorbic acid and estradiol across hairless mouse skin were evaluated from this approach and compared with those obtained from ill vitro penetration experiment using excised hairless mouse skin. The data confirmed that the proposed method can predict the steady-state rate of penetration of these drugs across the stratum corneum.