NMR determination of trimethoprim and sulfamethoxazole in tablets and powders

An NMR spectroscopic method for the determination of mixtures of trimethoprim and sulfamethoxazole is described. Spectra are determined in dimethylsulfoxide-d6, containing 1,4-dinitrobenzene as an internal standard. Both synthetic mixtures and commercial formulations were assayed, and the results were compared to those obtained using the BP procedure.