Metoclopramide: antipsychotic efficacy of a drug lacking potency in receptor models.

Metoclopramide is a substituted benzamide derivative, structurally similar to procainamide and sulpiride. In behavioral, biochemical, and neuroendocrine tests it displays classic neuroleptic dopamine (DA) antagonist properties; in contrast to other DA antagonists, it lacks potency in currently used DA receptor models. In clinical studies using low doses or dubious measures, it was considered not to be efficacious as an antipsychotic. We now find that it indeed has a clinical profile similar to known neuroleptics when used in a dose range predicted from animal models. The findings raise questions regarding the validity and universality of several predictive models, as well as hypotheses purporting to explain molecular mechanisms of action of neuroleptic agents. The drug's inactivity in receptor models suggests that an as yet unidentified DA receptor subpopulation may be important as the mediator of many DA dependent neurobiologic phenomena.