Abstract
The assay procedure of underivatized, intact nitrazepam and clonazepam in human plasma is described, using gas chromatography with a support-coated open tubular column (OV-17), a solid injection system and electron-capture detection. Clonazepam is used as a internal standard in the assay of nitrazepam and vice versa. Linear calibration curves after a single extraction step were obtained in the concentration range 10--100 ng/ml plasma, with standard deviations less than 4.9%. The sensitivity limit of the method is about 1 ng/ml plasma for both drugs. The method was applied to pharmacokinetic and bioavailability studies of nitrazepam in humans. Seven healthy volunteers received two nitrazepam-containing tablet preparations (5 mg) and plasma concentrations were determined regularly from 15 min to 80 h following drug administration. The mean elimination half-life of nitrazepam was 27 h (range 13-34 h). Considerable intra-individual differences in peak level times between the two preparations were observed, whereas the extent of bioavailability was rather similar.
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