Determination of etoricoxib in human plasma by liquid chromatography–tandem mass spectrometry with electrospray ionisation

The validation of a liquid chromatography–tandem mass spectrometry (LC–MS–MS) method for the determination of the selective cyclooxygenase-2 inhibitor etoricoxib in human plasma with phenazone as internal standard is described. The plasma samples were extracted by solid-phase extraction using polymer-based cartridges. Chromatography was carried out on a short, narrow bore RP C18 column (30×2 mm). Detection was achieved by a Sciex API 3000 triple quadrupole mass spectrometer equipped with a turbo ion spray source working in positive ion mode. The respective mass transitions used for quantification of etoricoxib and phenazone were m/z 359.2→280.2 and m/z 189.0→104.1. The analytical method was validated over the concentration range 0.2–200 ng/ml. The limit of quantification was 0.2 ng/ml. The method is applicable to pharmacokinetic studies in humans.