DETERMINATION OF AN IN-VIVO METABOLITE OF A HUMAN-IMMUNODEFICIENCY-VIRUS PROTEASE INHIBITOR IN HUMAN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH TANDEM MASS-SPECTROMETRY

A method for the determination of a metabolite of the human immunodefi ciency virus protease inhibitor indinavir, in human plasma is describe d. Isolation of the analyte and the internal standard from plasma was achieved via liquid-liquid extraction with a mixture of isopropanol-ch loroform (5:95, v/v). The analytes were chromatographed under reversed -phase conditions on a Waters Symmetry C-8 column. A Sciex API III+ ta ndem mass spectrometer equipped with a heated nebulizer was used as a detector and was operated in the positive ion mode. Multiple reaction monitoring using the precursor-product ion combinations of mit 523.4-- >273.4 and 512.4-->345.2 was used to quantify analyte and internal sta ndard, respectively. The method was validated in the concentration ran ge of 5-500 ng/ml plasma with adequate assay precision and accuracy. T he assay was used to analyze samples collected during drug interaction studies of indinavir.