Stereoselective determination of ofloxacin and its metabolites in human urine by capillary electrophoresis using laser-induced fluorescence detection

A capillary electrophoresis method for the simultaneous separation and enantioseparation of the antibacterial drug ofloxacin and its metabolites desmethyl ofloxacin and ofloxacin N-oxide in human urine has been developed and validated. Enantioseparation was achieved by adding sulfobutyl β-cyclodextrin to the running buffer. The detection of the analytes was performed by laser-induced fluorescence (LIF) detection using a HeCd-laser with an excitation wavelength of 325 nm. In comparison with conventional UV detection, LIF detection provides higher sensitivity and selectivity. The separation can be performed after direct injection of urine into the capillary without any sample preparation, because no matrix compounds interfere with the assay. Additionally, the high sensitivity of this method allows the quantification of the very low concentrations of enantiomers of both metabolites. The limit of quantification was 250 ng/ml for ofloxacin enantiomers and 100 ng/ml for each metabolites’ enantiomers. This method was applied to the analysis of human urine samples collected from a volunteer after oral administration of 200 mg of (±)-ofloxacin to elucidate stereoselective differences in the formation and excretion of the metabolites. It could be demonstrated that the renal excretion of the S-configured metabolites, especially S-desmethyl ofloxacin, within the first 20 h after dosage, is significantly lower than that of the R-enantiomers.