Simultaneous determination of sibutramine and its active metabolites in human plasma by LC-MS/MS and its application to a pharmacokinetic study

A simple and sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) technique was developed and validated for the determination of sibutramine and its N-desmethyl metabolites (M1 and M2) in human plasma. After extraction with methyl t-butyl ether, chromatographic separation of analytes in human plasma was performed using a reverse-phase Luna C₁₈ column with a mobile phase of acetonitrile-10mm ammonium formate buffer (50:50, v/v) and quantified by ESI-MS/MS detection in positive ion mode. The flow rate of the mobile phase was 200μL/min and the retention times of sibutramine, M1, M2 and internal standard (chlorpheniramine) were 1.5, 1.4, 1.3 and 0.9min, respectively. The calibration curves were linear over the range 0.05-20ng/mL, for sibutramine, M1 and M2. The lower limit of quantification was 0.05ng/mL using 500μL of human plasma. The mean accuracy and the precision in the intra- and inter-day validation for sibutramine, M1 and M2 were acceptable. This LC-MS/MS method showed improved sensitivity and a short run time for the quantification of sibutramine and its two active metabolites in plasma. The validated method was successfully applied to a pharmacokinetic study in human.