Abstract
Sulphamethoxazole and trimethoprim are the active antibacterial agents in co-trimoxazole preparations. The standard assay procedures for sulphamethoxazole and trimethoprim involve complex spectrophotometric and spectrofluorimetric determinations respectively. The trimethoprim procedure in particular is both time consuming and laborious. The method described in the present paper based on hydrophilic ion-pairing, reversed-phase, high performance liquid chromatography (HPLC) permits the estimation of trimethoprim, sulphamethoxazole and its principal metabolite N4-acetylsulphamethoxazole.