Simultaneous determination of iloperidone and its metabolites in rat plasma using a novel UPLC-MS/MS method: an application for drug-drug interaction

This study aimed to develop and validate a novel ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous determination of iloperidone (ILP) and its metabolites P88, P95 in rat plasma and to investigate drug-drug interaction (DDI) between shikonin and ILP in Sprague-Dawley rats. The separation of the analytes was performed on a UPLC BEH C18 column in the mobile phase (acetonitrile and water with 0.1% formic acid) with the flow rate of 0.4 mL/min. The quantitative analysis was performed in positive ion mode. A total of 10 Sprague-Dawley rats were divided into two groups: control group (1.0 mg/kg ILP alone) and experimental group (20 mg/kg shikonin plus 1.0 mg/kg ILP) to investigate the influence of shikonin on ILP metabolism in rats. We successfully established a quick UPLC-MS/MS analytical method for simultaneously detecting ILP and its two metabolites in rat plasma. Linearity, matrix effect, recovery, accuracy, precision and stability of this quantitative method was satisfied with Food and Drug Administration (FDA) guidelines. In addition, in vitro studies demonstrated that shikonin significantly inhibited CYP3A4- and CYP2D6-mediated metabolism in both rat liver microsomes (RLM) and human liver microsomes (HLM). Furthermore, we found the main pharmacokinetic parameters of ILP, such as AUC_(0-t) and the peak plasma concentration (C_max), were obviously changed, which were about twice higher in experimental group than the values in control group. The data demonstrated that shikonin obviously changed the main pharmacokinetics of ILP and its metabolites in rats. In the future clinical use, we should pay more attention to the concomitant application of shikonin and ILP in humans.