Metoclopramide: pharmacology and clinical application.

Metoclopramide antagonizes the effect of dopamine in the central nervous system and other organ systems. Metoclopramide's effect on the medullary chemoreceptor trigger zone makes it useful as a routine anti-emetic and in preventing vomiting induced by antineoplastic drugs, particularly cisplatin. Metoclopramide's gastrointestinal smooth muscle stimulatory effects are related to its ability to antagonize the inhibitory neurotransmitter, dopamine; to augment acetylcholine release and sensitize the muscarinic receptors of the gastrointestinal smooth muscle; and to coordinate gastric-pyloric-small intestinal motor function. The indications for which metoclopramide is approved in the United States are reviewed. Adverse effects, which may occur in up to 20% of patients, include drowsiness, lassitude, and akathisia; all are usually mild, transient, and reversible. Tremor, dystonic reactions, and extrapyramidal effects are infrequent; breast enlargement, galactorrhea, and menstrual irregularities are related to prolactin release.