Plasma levels of trimethoprim and sulfonamide after administration of trimethoprim-sulfamethoxazole and trimethoprim-sulfamoxole.

In a cross-over study with ten healthy volunteers, the plasma levels of trimethoprim (TMP) and sulfonamides were compared using orally given trimethoprim-sulfamethoxazole (TMP-SMX: Septra) and trimethoprim-sulfamoxole (TMP-SMO: Supristol) in recommended doses. The dosage schedule for TMP-SMX was 2 tablets every 12 h for nine doses, and for TMP-SMO it was 2 tablets as in the first dose, followed by 1 tablet every 12 h for eight more doses. Serial plasma levels of TMP and sulfonamides after the first dose of each of the two products showed no significant differences. However, after the ninth dose of each product, the paired t test revealed significantly higher levels of TMP and sulfonamides after TMP-SMX as compared with TMP-SMO.