Modification of an automated method for measurement of sulfamethoxazole and its major metabolite in biological fluids.

Mechanization of the Bratton and Marshall procedure for the analysis of sulfonamides in biological fluids usually incorporated a dialysis step. Results for sulfamethoxazole and its major metabolite (N4-acetylsulfamethoxazole) by the traditional method of acid hydrolysis often showed “negative” quantities of the metabolite. After an exhaustive examination it was found that the dialysis step must be rigorously controlled and for most laboratory applications it was better to omit the dialysis, when removal of protein and dilution of samples and standards outside the mechanized system was necessary. Reasons for the dialysis omission are discussed.