Abstract
A rapid, sensitive and specific method for quantification of metolazone in human plasma using metaxalone as internal standard is described. Sample preparation involved a simple liquid-liquid extraction procedure. The extract was analyzed by high performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC–MS–MS). Chromatography was performed isocratically on a 5 μm C18 analytical column (50 mm × 4.6 mm i.d.) with buffer–acetonitrile 20:80 (v/v) as mobile phase. The response to metolazone was a linear function of concentration over the range 1.00 to 2000.00 ng mL-1. The lower limit of quantification in plasma was 1.0 ng mL-1. The method was successfully applied in a bioequivalence study of a metolazone formulation after administration as a single oral dose.