Percutaneous absorption of salicylic acid in man after topical administration of three different formulations

Objective: To determine the amount of drug which is absorbed during 1 day following topical application of three different preparations containing salicylic acid. Methods: Ten grams of the formulations, either (a) Kerasal(TM) 5% ointment, (b) salicylic acid 5% or (c) 10% in petrolatum, were administered consecutively to a 600-cm(2) area on alternating sides of the back of healthy volunteers (n = 9). Thirty minutes after application, a skin area of 2.54 cm(2) was stripped with D-Squame(TM) adhesive disks to determine the amount of salicylic acid in the stratum corneum. The entire application site was then covered by a thin gauze bandage and was not washed for the next 24 h. Urine was collected for 26 h following administration, hydrolyzed and assayed by HPLC analysis. Results: The absolute amounts absorbed and excreted were 52.6 +/- 29.4 mg (mean +/- SD), 127.1 +/- 43.9 mg and. 208.0 +/- 81.7 mg, and the doses absorbed in relation to the doses applied (500 mg salicylic acid in case of formulations a and b and 1,000 mg for formulation c) were 9.3 +/- 3.8, 25.7 +/- 8.5 and 20.2 +/- 7.7%, respectively. The amounts of salicylic acid in the skin 30 min after application were 36.3 +/- 16.5, 18.2 +/- 11.0 and 31.3 +/- 15.4 mu g/ cm(2) as determined by the tape stripping procedure. Conclusions: Significant differences in the doses absorbed were detected between the two formulations a and b (same concentration) with different vehicles (p value < 0.001) as well as between b and c (same vehicle) with different concentrations (p value = 0.018) using Student's paired t test. These results demonstrate that salicylic acid is well absorbed by healthy skin.