Penetration of trolamine salicylate into the skeletal muscle of the pig.

Studies to determine the extent of local tissue penetration of topically applied trolamine [14C]salicylate were conducted in domestic pigs. The preparation was applied onto a 100-cm2 shaved area of skin overlying the biceps femoris at a concentration of 0.7 mg of salicylate/cm2 to closely approximate the actual use in humans. At least 82% of the topically applied trolamine salicylate was absorbed over a 2-h period. Based on blood and muscle salicylate levels, a localization of the absorbed drug occurred in muscle underlying the treated area within 120 min. Muscle from the treated area had a concentration of salicylate that was 13 times that of blood and 49 times that of muscle taken from untreated areas. Blood samples taken from the treated area at 10, 20, and 30 min showed that salicylate levels ranged from 15.8 to 5.3 micrograms/g. Less than 0.5% of the applied drug was excreted in the urine during the 2-h period.