Quantification of mequitazine in human plasma by gas chromatography- quadrupole mass spectrometry and its application to a human pharmacokinetic study.

A specific and sensitive gas chromatography-mass spectrometry (GC-MS) with quadrupole mass analyzer type was developed and validated for the quantitative analysis of mequitazine in human plasma. After liquid-liquid extraction of plasma samples containing mequitazine and promethazine (internal standard, IS) using hexane with pH adjustment, the extract was evaporated and an aliquot of reconstituted residue was injected into the GC-MS system. The assay showed linearity over a concentration range from 1 to 50 ng/mL. Intra- and inter-day precision for mequitazine was <9.09 and 9.29%, respectively, and intra- and inter-day accuracy ranged from -7.97 to 9.05% and from -1.51 to 7.89%, respectively. The lower limit of quantification was 1 ng/mL in the present assay. The developed analytical method was successfully applied to a pharmacokinetic study after a single oral administration of mequitazine in human subjects.