Determination of flumequine and a hydroxy metabolite in biological fluids by high-pressure liquid chromatographic, fluorometric, and microbiological methods

A sensitive and specific high-pressure liquid chromatographic method is described for the determination of the antibacterial drug flumequine and a major metabolite, 7-hydroxyflumequine, in human plasma and urine. The assay was linear over a concentration range of 1 to 120 micrograms/ml for both compounds. This method is compared with fluorometric and microbiological assays for flumequine. These latter methods did not differentiate between flumequine and any fluorescent or antimicrobiologically active metabolites. However, because essentially all drug in the plasma was found to be flumequine in radiolabeled studies, levels of unchanged drug in the plasma could be quantitated by either high-pressure liquid chromatography or fluorometry. Although only high-pressure liquid chromatography was able to specifically measure flumequine in the urine, the antimicrobial activity of the urine, which is more therapeutically relevant due to antimicrobially active metabolites, could be quantitated by either the fluorometric or the microbiological assay.