Analysis of omeprazole, midazolam and hydroxy-metabolites in plasma using liquid chromatography coupled to tandem mass spectrometry

A method has been developed and validated for the quantitation of midazolam, alphahydroxy-midazolam, omeprazole, and hydroxyomeprazole from one 250 μL sample of human plasma using high performance liquid chromatography coupled to tandem mass spectrometry. The method was validated for a daily working range of 0.400–100 ng/mL, with limits of detection between 2 and 15 pg/mL. The inter-assay variation was less than 15% for all analytes at four control concentrations and the samples were stable for three freeze–thaw cycles under the analysis conditions and 24 h in the post-preparative analysis matrix. This method was used to analyze samples in support of clinical studies probing the activity of the cytochrome P-450 enzyme system.