Improved quantitative determination of (R)- and (S)‐rabeprazole sodium and its metabolites in rat plasma by LC-MS/MS and its application to a toxicokinetic study

Abstract

There exist two enantiomers: (R)‐ and (S)‐rabeprazole. (R)‐rabeprazole offers specific pharmacokinetic advantages and enhanced therapeutic efficacy, warranting further investigation and development. Here, we developed a simple and rapid chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to simultaneously quantify rabeprazole enantiomers and their metabolites (rabeprazole sulfoxide and desmethyl rabeprazole enantiomers) and a LC-MS to quantify rabeprazole thioether. As for the chiral LC-MS/MS method, Chiral-AGP column (150 × 4 mm, 5 μm) was used and its mobile phase was acetonitrile (mobile phase A) and 10 mmol/L ammonium acetate (mobile phase B) (linear gradient profile: 0 min, 10 % B; 5 min, 15 % B; 9 min, 15 % B; 9.01 min, 10 % B; 13 min, 10 % B). The multiple reactions monitoring transitions of m/z 360.3 → 242.1, 376.2 → 240.1, 346.2 → 228.2 and 368.2 → 190.2 were opted for quantifying rabeprazole enantiomers, rabeprazole sulfoxide, desmethyl rabeprazole enantiomers and internal standard omeprazole. The analyte samples were prepared by a simple liquid–liquid extraction method. As for the LC-MS method, analytes were separated on a Inertsil® ODS-3 column (4.6 × 150 mm, 5 μm). The mobile phase was acetonitrile-5 mmol/L ammonium acetate water solution (65:35, v/v). ESI+ was used and ion peaks with m/z 344.2 (rabeprazole thioether) and 285.1 (internal standard diazepam) were monitored. Both these 2 methods were validated for specificity, linearity, precision, accuracy, matrix effect and extraction recovery, and, particularly, the stability of analytes under various conditions. We successfully applied these methods to a 13-week toxicokinetic study of rabeprazole in rats after intravenous administration of (R)- (80, 20, 5 mg/kg/d) and racemic (80 mg/kg/d) rabeprazole sodium. The results showed that rabeprazole and its metabolites did not accumulate in rats. However, desmethyl rabeprazole and rabeprazole thioether showed higher exposure and lower clearance rate in the last administration than in the first one. (R)-rabeprazole showed a higher exposure and a slower elimination rate than (S)-rabeprazole in rats. These findings offer experimental evidence and a theoretical foundation for further preclinical investigations and clinical applications of (R)-rabeprazole.