| Abstract: | A radioimmunoassay for the determination of the hypnotic flurazepam in plasma was developed. Plasma levels of intact flurazepam were measured following oral administration of therapeutic doses to humans. The procedure employs an antiserum obtained from a rabbit immunized with 3-hemisuccinyloxyfluorazepam covalently coupled to bovine serum albumin and tritium-labeled flurazepam as the radioligand. Assay specificity was achieved by chromatographic isolation of flurazepam from plasma extracts on Sephadex LH-20 prior to analysis. The method has a sensitivity limit of 0.1 ng of flurazepam/ml using a 1-ml plasma sample, and the intra- and interassay coefficients of variation did not exceed 9% over a range of 0.1-5 ng/ml. In eight subjects who received a single 30-mg dose of flurazepam, peak plasma concentrations of 0.5-3.0 ng of intact drug/ml were reached after 0.5-1 hr, except in one subject where the peak occurred at 4 hr. The plasma concentrations of flurazepam declined with a harmonic mean apparent half-life of 2.3 hr. |
