Interaction of amoxapine with muscarinic cholinergic receptors: an in vitro assessment.

Amoxapine, an antidepressant with a rapid onset of therapeutic efficacy and great utility in psychotic depression, has been reported to produce anticholinergic side effects in man similar to those observed with imipramine and amitriptyline. To establish its cholinergic disposition, amoxapine and its metabolites 7-hydroxyamoxapine and 8-hydroxyamoxapine, have been evaluated by determining their effects on quinuclidinyl benzilate (QNB) binding to membrane fractions of rat and human brain, on the carbamoylcholine-stimulated accumulation of inositol phosphates in rat cerebral cortex and on the acetylcholine-induced contraction of the guinea pig ileum. In all three preparations, amoxapine was found to be a considerably weaker antagonist of muscarinic cholinergic receptors than either imipramine (4-27 fold) or amitriptyline (51-300 fold). These results indicate that for amoxapine, no correlation exists between the magnitude of muscarinic receptor inhibition and the extent of 'anticholinergic' side effects found in the clinic. Neither the metabolites of amoxapine nor species differences could account for this discrepancy.