Development and validation of an LC-MS/MS method for the determination of tolvaptan in human plasma and its application to a pharmacokinetic study.

Tolvaptan is a selective vasopressin V(2)-receptor antagonist mainly used for the treatment of hyponatremia. This study described the development and validation of an LC-MS/MS method for the determination of tolvaptan in human plasma. Sample preparation involved protein precipitation with acetonitrile containing 2-demethyl tolvaptan (internal standard, IS). Chromatographic separation was performed on a Zorbax XDB C(18) column with an isocratic mobile phase consisting of water (containing 0.1% formic acid) and methanol (25:75, v/v). Determination of the analytes was achieved by tandem-mass spectrometry with positive electrospray ionization. The multiple reaction monitoring (MRM) transitions were performed at m/z 449.2→252.1 for tolvaptan and m/z 435.2→238.1 for IS. The assay was linear over the concentration range of 0.457-1000ng/mL, with a lower limit of quantification of 0.457ng/mL. The intra- and inter-day precisions at three concentration levels (0.914, 111 and 800ng/mL) were less than 15% and their accuracies were within the range of 97.7-107.8%. The mean recovery ranged from 99.2 to 104.6% and the matrix effect from 89.3 to 99.5%. Tolvaptan was stable under all tested conditions. This validated method was successfully applied to a pharmacokinetic study in healthy volunteers after oral administration of single-dose tolvaptan tablets.