High-performance liquid chromatographic determination of lorazepam in monkey plasma

A simple, sensitive and selective method for the determination of lorazepam in monkey plasma has been developed using high-performance liquid chromatography in a reversed-phase mode. The limit of detection for lorazepam in plasma is about 2 ng/ml. The method has been applied to plasma samples obtained from cynomolgus monkeys after oral doses of 0.15 mg/kg and intravenous doses of 0.05 mg/kg of lorazepam. In this species, mean peak plasma concentrations of 12 ng/ml occurred at 2 h after oral dosing and declined with a half-life of 2,5 h; the mean terminal half-life after intravenous dosing was 1.4 h.