Percutaneous absorption of methyl salicylate from medicated plaster in mice and humans.

Abstract

The plaster containing [14C] methyl salicylate was applied to the back of hairless mice of HRS/J (hr) strain. [14C] Methyl salicylate was percutaneously absorbed and distributed with a high concentration in the skin at the applied site. The peak level (1.5 mg%) of salicylate in the serum was attained 2 hours following application. Approximately 40% of the dose applied was excreted in the urine of 48-hour treated mice. Ten sheets of the plaster containing non-radioactive methyl salicylate (35.0 mg/sheet) were applied to the back of male human subjects for 12 hours. The amount absorbed percutaneously could be estimated to be approximately 37% of the dose applied. The serum concentrations of total salicylates and free salicylic acid reached a peak at 8-12 hours. Within 12 hours after removal of the plaster, practically all of the total salicylates and free salicylic acid were excreted from the body. Application of the plaster for 12 hours a day was repeated for consecutive six days. Trace or no amout of total salicylates and free salicylic acid was detected in the serum 12 and 30 hours after removal of the last plasters. No significant changes were noted in the hepatic functions of all the subjects before and after the repeated application.