Quantitative determination of ondansetron in human plasma by enantioselective liquid chromatography-tandem mass spectrometry

A sensitive and enantioselective method was developed and validated for the determination of ondansetron enantiomers in human plasma using enantioselective liquid chromatography-tandem mass spectrometry. The enantiomers of ondansetron were extracted from plasma using ethyl acetate under alkaline conditions. HPLC separation was performed on an ovomucoid column using an isocratic mobile phase of methanol–5 mM ammonium acetate–acetic acid (20:80:0.02, v/v/v) at a flow rate of 0.40 mL/min. Acquisition of mass spectrometric data was performed in multiple reaction monitoring mode, using the transitions of m/z 294 → 170 for ondansetron enantiomers, and m/z 285 → 124 for tropisetron (internal standard). The method was linear in the concentration range of 0.10–40 ng/mL for each enantiomer using 200 μL of plasma. The lower limit of quantification (LLOQ) for each enantiomer was 0.10 ng/mL. The intra- and inter-assay precision was 3.7–11.6% and 5.6–12.3% for R-(−)-ondansetron and S-(+)-ondansetron, respectively. The accuracy was 100.4–107.1% for R-(−)-ondansetron and 103.3–104.9% for S-(+)-ondansetron. No chiral inversion was observed during the plasma storage, preparation and analysis. The method was successfully applied to characterize the pharmacokinetic profiles of ondansetron enantiomers in healthy volunteers after an intravenous infusion of 8 mg racemic ondansetron.