Tricyclic antidepressant radioreceptor assay

A radioreceptor assay for tricyclic antideressants described here is based on the ability of these drugs to compete with [³H]-3-quinuclidinyl benzatile (³H-QNB) for binding to muscarinic cholinergic receptors in rat brain membranes. The assay is sensitive, in that it can detect, for example, 2 ng/ml nortriptyline in plasma. Seven plasma samples from depressed patients treated with notriptyline were assayed with the radioreceptor and gas liquid chromatographic methods, and the results for these two methods were almost identical. This assay should be used continously, if at all, in patients treated with other drugs that have potent anticholinergic effects.