Studies on Percutaneous Absorption of Drugs. II. Time-Course of Cutaneous Reservoir of Drugs

Abstract

1) Time-course of cutaneous reservoir of both salicylic acid and carbinoxamine showed same pattern as those of decreasing from the recirculating solution in the initial time, and the cutaneous reservoir attained to a definite amount after the lapse of a given time. 2) This definite amount reserved was different with the variation of the drug concentration and the pH values in test solution, and increased as increasing of the fraction of the unionized form of both drugs. 3) The amount decreased from test solution was almost negligible at pH 6.0 where the most of both drugs ionized, however, the amount reserved was slightly detected in the skin. 4) The diffusion of drug into the external area of applied skin was negligible, and the drug permeability through the skin was restricted to the applied area. 5) After test solution was removed from the applied area, the disappearance of drug from the cutaneous reservoir was traced quantitatively during 13 days, and it was cleared that considerable amounts of both drugs reserved remained for a long time. 6) Studying on the reservoir part of drugs, it was recognized that the skin surface, particulary the stratum corneum, had a high ability of the drug reservoir.