Effect of salicylic acid on the percutaneous absorption of hydrocortisone. In vivo studies in the rhesus monkey.

To document the effect of salicylic acid on hydrocortisone penetration in vivo in the rhesus monkey, hydrocortisone 14C, with and without salicylic acid, was applied in acetone and the solvent evaporated. The compounds also were applied in a formulation (60% ethanol, 5% propylene glycol, 5% glycerin, 30% water) in which salicylic acid enhances penetration in vitro. There was a difference in the kinetics of hydrocortisone absorption with the two formulations. In acetone, excretion of 14C peaked at 48 hours and then declined. With the other formulation, excretion peaked at 48 hours, maintained to 72 hours, and then declined. There was no statistical difference in the percutaneous absorption of hydrocortisone with the addition of salicylic acid. These in vivo data are in contrast to the reported enhancing effect of salicylic acid obtained with in vitro studies.