title: Liquid chromatographic assay and pharmacokinetics of halazepam and its metabolite in humans.
abstract: A reversed-phase high-performance liquid chromatographic method is described for simultaneous quantification of halazepam and its major active metabolite, nordiazepam, in plasma. The method uses a solid-phase extraction procedure to prepare plasma samples. After extraction, the methanolic extract is evaporated, and the residue is then reconstituted in a small volume of mobile phase (a 40:60, v/v, mixture of 0.02 M phosphate buffer, pH 4.0, and methanol) and chromatographed. The total chromatography time for a single sample is approximately 10 min. A sensitivity of 1 ng/mL for halazepam and nordiazepam is attained when 1 mL of plasma is extracted. Analytical recovery of halazepam and nordiazepam added to the plasma ranged from 89 to 96%. The maximum within-day and day-to-day coefficients of variation for each compound at the concentration range of 2 to 100 ng/mL were 8.7 and 10.3%, respectively. Suitability of the method was assessed in a preliminary pharmacokinetic study in which three subjects were given a single 20-mg oral dose of halazepam following an overnight fast. It appeared from our kinetic analysis that halazepam is a drug with a fairly rapid absorption phase that is followed by a slow elimination phase. Mean oral plasma clearance of halazepam was 24 L/h. The mean apparent elimination half-life of nordiazepam (45.22 h) is considerably longer than that of halazepam (21.15 h).
authors.affiliation: Department of Psychiatry, Duke University Medical Center, Durham, NC 27710.
authors.forename: S K
authors.initials: SK
authors.lastname: Gupta
authors.forename: E H
authors.initials: EH
authors.lastname: Ellinwood
mesh_terms: D000284:Administration, Oral; D000328:Adult; D014151:Anti-Anxiety Agents / Q000097:blood / Q000493:pharmacokinetics*; D001569:Benzodiazepines; D001570:Benzodiazepinones / Q000097:blood / Q000493:pharmacokinetics*; D002851:Chromatography, High Pressure Liquid; D006207:Half-Life; D006801:Humans; D007202:Indicators and Reagents; D008297:Male; D003708:Nordazepam / Q000097:blood
chemical_list: D014151:Anti-Anxiety Agents; D001570:Benzodiazepinones; D007202:Indicators and Reagents; D001569:Benzodiazepines; C065715:3-hydroxyhalazepam; C010175:halazepam; D003708:Nordazepam