An improved LC-MS/MS method for quantitative determination of ilaprazole and its metabolites in human plasma and its application to a pharmacokinetic study

Aim: To improve and validate an analytical method based on liquid chromatography and electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) for the quantitative measurement of ilaprazole and its two metablites in human plasma. Methods: Separation of analytes and the internal standard (IS), omeprazole, was performed on a Thermo HyPURITY C18 column (150 x 2.1 mm, 5 mu m) with a mobile phase consisting of 10 mmol/L ammonium formate water-acetonitrile solution (50: 50, v/v) at a flow rate of 0.25 mL/min. The API4000 triple quadruple mass spectrometer was operated in multiple reactions monitoring mode via positive electrospray ionization interface using the transition m/z 367.2 -> m/z 184.0 for ilaprazole, m/z 383.3 -> m/z 184.1 for ilaprazole sulfone, m/z 351.2 -> m/z 168.1 for ilaprazole thiol ether and m/z 346.2 -> m/z 198.0 for omeprazole. Results: The method was linear over the concentration range of 0.23-2400.00 ng/mL for ilaprazole, 0.05-105.00 ng/mL for ilaprazole thiol ether and 0.06-45.00 ng/mL for ilaprazole sulfone. The intra- and inter-day precisions were all less than 15% in terms of relative standard deviation (RSD), and the accuracy was within 15% in terms of relative error (RE) for ilaprazole, ilaprazole sulfone and ilaprazole thiol ether. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.23, 0.05 and 0.06 ng/mL with acceptable precision and accuracy for ilaprazole, ilaprazole sulfone and ilaprazole thiol ether, respectively. Conclusion: The validated method offered sensitivity and a wide linear concentration range. This method was successfully applied for the evaluation of the pharmacokinetics of ilaprazole and its two metabolites after single oral doses of 5 mg ilaprazole to 12 healthy Chinese volunteers.