A highly sensitive LC-MS-MS assay for analysis of midazolam and its major metabolite in human plasma: applications to drug metabolism.

The present report describes a rapid, selective and a highly sensitive assay for midazolam (MDZ) and its major metabolite 1-hydroxymidazolam (1-OH-MDZ) in human plasma employing liquid chromatography-tandem mass spectrometry (LC-MS-MS) detection. The method involves liquid-liquid extraction sample clean-up, separation on a Purospher RP 18-e column and detection with an electrospray interface in the positive ion mode. The overall recoveries were about 100% and 80% for midazolam and 1-hydroxymidazolam, respectively. Accuracy, precision and linearity were acceptable for biological samples with quantitation limits of 0.1-100 ng mL(-1) plasma for both analytes. The validated method was successfully applied to quantify plasma concentration of midazolam and 1-hydroxymidazolam in authentic samples from a healthy volunteer following a single 15 mg oral dose of midazolam (apparent total clearance: 3.47 L h(-1)kg(-1) and AUC(0-alpha)IOH-MDZ/MDZ: 0.338).