A rapid and sensitive radioreceptor assay for benzodiazepine in plasma.

We describe a rapid and sensitive radioreceptor assay for measuring benzodiazepines in plasma. This method is based on the competition between tritiated diazepam and pharmacologically active benzodiazepines present in plasma, for binding sites on rat brain synaptosomal membranes. No interference is obtained with drug-free plasma or plasma samples containing high concentrations of other commonly used drugs. High correlations (r = 0.98; P less than .001) were obtained between the "diazepam equivalents" measured in plasma with the radioreceptor assay and the levels of diazepam and nordiazepam obtained by gas-liquid chromatography. The radioreceptor assay is rapid, sensitive, specific, and requires no sophisticated equipment or methods. It should therefore prove useful in monitoring blood benzodiazepine levels for both therapeutic and toxicologic purposes.