A radioreceptor assay to study the affinity of benzodiazepines and their receptor binding activity in human plasma including their active metabolites.

1 A radioreceptor assay has been established to measure the receptor affinities of numerous benzodiazepines in clinical use. 2 The time course of receptor binding activity was studied by this method in the plasma of eight healthy subjects randomly treated with 1 mg lormetazepam (Noctamid, 2 mg flunitrazepam (Rohypnol, and 10 mg diazepam (Valium, and placebo on a cross‐over basis. Blood samples were collected up to 154 h after treatment. 3 Receptor affinities of numerous benzodiazepines on vitro show good correlation with therapeutic human doses (r = 0.96) and may be predictive of drug potency in man. 4 Mean peak plasma levels of lormetazepam binding equivalents were 4.8 +/‐ 1 ng/ml at 2 h after lormetazepam, 7.2 +/‐ 1.8 ng/ml at 8 h after flunitrazepam, and 17.9 +/‐ 2.7 ng/ml at 15 h after diazepam. Plasma elimination half‐lives of benzodiazepine binding equivalents were 9.3, 23 and 63 h, respectively. 5 Slow elimination of benzodiazepine binding equivalents following flunitrazepam and diazepam may be due to persistent active metabolites.

DOI: 10.1111/j.1365-2125.1982.tb01422.x

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