A VALIDATED ION-PAIRING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF ENOXACIN AND ITS METABOLITE OXO-ENOXACIN IN PLASMA AND URINE

A rapid, sensitive, and specific determination of enoxacin and its principal metabolite, oxo-enoxacin, in plasma and urine is described. The method, which employs the structurally related compound ciprofloxacin as internal standard, involves a protein precipitation step for plasma and solid-phase extraction for urine. Liquid chromatographic analysis is carried out on a C-18 bonded silica column; the mobile phase consists of 0.1 M citric-acid/acetonitrile employing ammonium perchlorate and tetrabutyl-ammonium hydroxide as ion-pairing agents. Quantitation is performed by UV-detection at 340 nm. The analytical method was validated by examining the performance characteristics specificity, linearity, precision, accuracy, sensitivity, and recovery. Enoxacin calibration curves were linear between 0.02 and 3.2-mu-g/ml of plasma and from 0.5 to 125-mu-g/ml of urine. Limits of quantitation in plasma and urine were 0.01 and 0.5-mu-g/ml, respectively. For oxo-enoxacin, linear calibration curves were obtained in the range 0.05 to 1.6-mu-g/ml (plasma) and 1 to 50-mu-g/ml (urine); the respective quantitation limits were approximately 0.02 and 1-mu-g/ml. The present assay procedure has been applied to monitoring plasma and urine concentrations in several pharmacokinetic studies in humans and different animal species.