Metoclopramide

Metoclopramide is an antiemetic and is used for the symptomatic treatment of nausea and vomiting. It is also used to speed up the onset of action of some other drugs. It can be given as a tablet or as an infusion. Metoclopramide is available only on prescription.

Pharmacodynamics

The antiemetic effects of metoclopramide result from inhibition of dopamine D2 and serotonin 5-HT3 receptors in the brain. Administration of this drug results in prokinetic effects via inhibitory effects on pre- and postsynaptic D2 receptors, agonism of serotonin 5-HT4 receptors, and antagonism of muscarinic receptor inhibition. This action enhances the release of acetylcholine, resulting in increased lower esophageal sphincter and gastric tone, and accelerated gastric emptying and transit through the intestine. Metoclopramide antagonizes dopamine D2 receptors. Dopamine exerts a relaxing effect on the gastrointestinal tract by binding to the muscular D2 receptors.

Pharmacokinetics

Metoclopramide is rapidly absorbed in the gastrointestinal tract with an absorption rate of approximately 84%. The bioavailability of the oral preparation is reported to be about 40.7%, but may range from 30-100%. Metoclopramide is 30% bound to plasma proteins, primarily alpha-1-acid glycoprotein. Metoclopramide undergoes first-pass metabolism and its metabolism varies depending on the individual. This drug is metabolized by cytochrome P450 enzymes in the liver . Mainly the two enzymes CYP2D6 and CYP3A4 are involved. Approximately 85% of an orally administered dose was measured in urine within 72 hours during a pharmacokinetic study. The mean elimination half-life of metoclopramide in people with healthy renal function is between 5 and 6 hours, but is prolonged in patients with renal impairment. Downward dose adjustment should be considered.

Side effects

Common adverse drug reactions associated with metoclopramide therapy include agitation (akathisia) and focal dystonia. Rare UAWs include hypertension, hypotension, hyperprolactinemia leading to galactorrhea, headache, and extrapyramidal effects such as oculogyric crises.

Metoclopramide may be the most common cause of drug-induced movement disorders. The risk of extrapyramidal effects is increased in people younger than 20 years and with high-dose or prolonged therapy. Tardive dyskinesia may be persistent and irreversible in some people. Most reports of tardive dyskinesias occur in people who have taken metoclopramide for longer than three months.

Dystonic reactions can be treated with benzatropine, diphenhydramine, trihexyphenidyl or procyclidine. Symptoms usually resolve with diphenhydramine injected intramuscularly. Agents of the benzodiazepine class can be helpful, but the benefit is usually small, and the side effects of sedation and weakness can be problematic.

In einigen Fällen stehen die Akathisieeffekte von Metoclopramid in direktem Zusammenhang mit der Infusionsrate, wenn das Medikament intravenös verabreicht wird. Die Nebenwirkungen traten in der Regel in den ersten 15 Minuten nach der Dosis von Metoclopramid auf.

Toxicological Data