Comparison of four methods for the determination of sulphonamide concentrations in human plasma.

Analysis of sulphadimethoxine in plasma from patients treated with this drug was performed with four chemical methods: Rieder's modification of the Bratton-Marshall technique and author's modification of the Morris technique, which are supposed to measure "potentially active fraction of sulphonamides", i.e., mainly unchanged sulphonamide; the Bratton-Marshall method, which enables the determination of "free sulphonamide", i.e., the sum of unchanged sulphonamide and glucuronide conjugate; and high performance liquid chromatography which made possible the determination of unchanged sulphadimethoxine. The spectrophotometric methods based upon Bratton-Marshall reaction gave very few higher results as compared with liquid chromatography. The differences between spectrophotometric and chromatographic methods were small; therefore, all four methods can be used for determination of sulphonamide concentrations in plasma during monitored treatment with these drugs.