Determination of trimethoprim and sulfamethoxazole (co-trimoxazole) in body fluids of man by means of high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of trimethoprim, sulfamethoxazole and its metabolite and a series of structurally related sulfonamides is described. The half-life time of elimination of sulfamethoxazole and its metabolite N4-acetylsulfamethoxazole is 9 h for both compounds. The renal excretion rate of sulfamethoxazole depends strongly on the urinary pH. The renal excretion rate of the metabolite N4-acetylsulfamethoxazole is not dependent on the urinary pH.