Penetration of trimethoprim and sulfamethoxazole into skin blister fluid.

In 32 patients the concentrations of sulfamethoxazole and trimethoprim in whole blood, plasma and skin blister fluid were studied in the course of treatment with co-trimoxazole and trimethoprim alone. Measurements were taken on the fourth day of treatment, 3 h after administration of the morning dose of the drug. The blood contained a lower concentration of sulfamethoxazole than plasma. About 70% of the sulfonamide penetrated into the exudate from plasma. Trimethoprim administered conjointly with sulfamethoxazole to a higher degree penetrated skin blister fluid to a greater extent than when given alone.