In vivo measurement of the keratolytic effect of salicylic acid in three ointment formulations.

The release and activity of salicylic acid from different ointment formulations was studied in vivo by staining the horny layer with silver nitrate and measuring the light reflectance profile over 56 h, after application of the ointment for 4 h. The peeling effect of an ointment containing 5% salicylic acid and 10% urea was tested and compared with 5% and 10% salicylic acid in petrolatum. It was shown that shedding from the stained sites was faster with the urea-containing preparation than with the classic petrolatum ointments. The method described can be used to assess the bioavailability of keratolytic agents incorporated in topical formulations.