Comparison of the conventional methods and high-performance liquid chromatography for the determination of trimethoprim, sulfamethoxazole and its metabolite in serum.

A modified high-performance liquid chromatographic (HPLC) method for sensitive and rapid determination of trimethoprim, sulfamethoxazole and its metabolite N4-acetylsulfamethoxazole has been compared with the bioassay for trimethoprim and a colorimetric procedure for sulfonamides. The sensitivity of the (HPLC) method has been increased by ultrafiltration of the sample. Thus, the sample dilution was markedly reduced compared to the values obtained with precipitation procedures. The recovery was 102.7 +/- 6.1% for trimethoprim, 93 +/- 5.4% for sulfamethoxazole and 90.2 +/- 7.9% for N4-acetylsulfamethoxazole. The between-day reproducibility was 5% (n = 5). The coefficients of correlation for HPLC and reference methods were 0.993 (bioassay) and 0.995 (colorimetric assay).