Determination of lansoprazole and two of its metabolites by liquid-liquid extraction and automated column-switching high-performance liquid chromatography: application to measuring CYP2C19 activity

A simple and sensitive column-switching high-performance liquid chromatographic (HPLC) method for the simultaneous determination of lansoprazole, a proton pump inhibitor and its major metabolites: 5-hydroxylansoprazole and lansoprazole sulfone in human plasma. The test compounds were extracted from 1 mL of plasma using diethyl ether-dichloromethane (7:3, v/v) mixture and the extract was injected into a column I (TSK-PW precolumn, 10 mum, 3.5 mm x 4.6 mm W.) for clean-up and column I (C-18 STR ODS-II analytical column, 5 mum, 150 mm x 4.6 mm i.d.) for separation. The peak was detected by a ultraviolet detector set at a wavelength of 285 nm, and the total time for a chromatographic separation was similar to25 min. The method was validated for the concentration range from 3 to 5000 ng/mL. Mean recoveries were 74.0 % for lansoprazole, 68.3 % for 5-hydroxylansoprazole, and 79.4 % for lansoprazole sulfone. Intra- and inter-day relative standard derivatives were less than 6.1 and 5.1 % for lansoprazole, 5.8 and 5.8 % for 5-hydroxylansoprazole, 4.4 and 5.9 % for lansoprazole sulfone, respectively, at the different concentration ranges. This method is suitable for use in therapeutic drug monitoring and pharmacokinetic studies, and provides use tool for measuring CYP2C19 activity. (C) 2004 Elsevier B.V. All rights reserved.