Determination of dexfenfluramine and nordexfenfluramine in urine by high-performance liquid chromatography using...

A method to determine the concentration of dexfenfluramine and its active metabolite nordexfenfluramine in human urine from healthy volunteers is described utilising a high-performance liquid chromatographic procedure with liquid-liquid extraction and ultraviolet detection. Analytes are measured after extraction of alkalinised urine with diethyl ether and subsequent back extraction with 0.5 M H2SO4 and with chromatography performed on a reversed-phase C18 column, using a mobile phase of acetonitrile-50 mM K2HPO4 (25:75, v/v) (flow-rate 1.3 ml/min) and ultraviolet detection at 210 nm. The sensitivity of the technique (10 ng/ml) is appropriate to measure both parent drug and metabolite in urine in humans for up to 5 days after a single 30-mg dose. The method is selective, reproducible (within- and between-day coefficient of variation ranged from 4.2 to 15%) and accurate (bias less than 8%) and thus suitable for dexfenfluramine pharmacokinetic investigations.