Distribution of salicylic acid in human stratum corneum following topical application in vivo: a comparison of six different formulations

Distribution of salicylic acid in human stratum corneum from treatment of s ix different formulations was assessed by quantitation of drug content in s equentially tape-stripped stratum corneum after a single 2-h dose was appli ed unoccluded to skin on the ventral forearm of four female subjects. The p rofile and total amounts of stratum corneum removed in 20 tape-strips varie d among different types of formulations. With or without normalization by t he total stratum corneum,weights removed, the extent of drug delivery to th e stratum corneum decreased in the following order: SA (5%) > > SAC (10%), Duofilm (16.7%) > TSSS (2%) > SAO (10%), Salic (2.5%), the percentage in pa rentheses indicating the salicylic acid concentration in each formulation. The greatest topical bioavailability was observed for the alcoholic solutio n containing glycerol (SA). The 10% collodion formulation (SAC) was found t o deliver an amount of salicylic acid into the stratum corneum 2-fold great er than 10% ointment formulation (SAO). Use of absorption ointment (TSSS) a lso increased the uptake of salicylic acid into the stratum corneum in comp arison with formulations based on simple ointment (SAO) and oil in water (o /w) cream (Salic). The partitioning of salicylic acid from collodion formul ations (SAC and Duofilm) appeared to be concentration-independent. The resu lts of this study indicate that topical bioavailability of salicylic acid i n the stratum corneum varies substantially among different formulations. (C ) 1999 Elsevier Science B.V. All rights reserved.