Determination of zolpidem in human plasma by liquid chromatography–tandem mass spectrometry for clinical application

•A simple and more sensitive assay method for zolpidem in plasma was developed.•The lower limit of quantifications for zolpidem was 0.05ng/mL.•The sample preparation procedure is very simple.•This method was successfully applied to a pharmacokinetic study in humans. Zolpidem (ZPD) is widely described for the short-term treatment of insomnia. We have developed and validated a simple and rapid liquid chromatography analytical method using tandem mass spectrometry (LC–MS/MS) for the quantification of ZPD in human plasma. Using dibucaine as an internal standard (IS), the analyte was extracted with methyl t-butyl ether (MTBE). Chromatographic separation of ZPD was performed on a reversed-phase Luna C18 column (50mm×2.0mm i.d., 5μm particles) with a mobile phase of 10mM ammonium formate buffer (pH 3.0)–methanol (15:85, v/v) at a flow rate of 250μm/min. The total run-time was 2.5min and the retention times of ZPD and IS were 0.66 and 0.74min, respectively. The mass-to-charge transition monitored for quantification of ZPD and IS was 308.2→235.2 and 344.0→271.0, respectively. The lower limit of quantification (LLOQ) using 100μL of human plasma was 0.05ng/mL and the calibration curves were linear over a range of 0.05–200ng/mL (r2>0.9964). The mean accuracy and precision for intra- and inter-run validation of ZPD were within acceptable limits. In the present LC–MS/MS method, we showed improved sensitivity for quantification of the ZPD in human plasma using lower volume of plasma compared with previously described analytical methods for ZPD. This validated method was successfully applied to a pharmacokinetic study in humans.