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 （150×2.1 mm, 5 um） 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.