METOMED INJECTION

Indications

• Nausea and vomiting (including chemotherapy-induced and postoperative)
• Gastroparesis
• Gastroesophageal reflux disease (GERD)
• Prevention of nausea and vomiting associated with radiotherapy

Dosage

Children: For paediatric patients, refer to the BNF for Children for specific dosing guidelines.

Adults: The typical adult dosage is 10 mg taken 3 times daily before meals and at bedtime, with a maximum duration of treatment not exceeding 12 weeks.

Mechanism of action

Metoclopramide causes antiemetic effects by inhibiting dopamine D2 and serotonin 5-HT3 receptors in the chemoreceptor trigger zone (CTZ) located in the area postrema of the brain. It enhances prokinetic effects through inhibitory actions on presynaptic and postsynaptic D2 receptors, agonism of serotonin 5-HT4 receptors, and antagonism of muscarinic receptors. This leads to increased release of acetylcholine, enhancing lower esophageal sphincter and gastric tone, accelerating gastric emptying and intestinal transit.

Pharmacodynamics

Metoclopramide increases gastric emptying by decreasing lower esophageal sphincter pressure and enhances gastrointestinal motility without increasing biliary, gastric, or pancreatic secretions. Its antidopaminergic activity can lead to adverse effects such as tardive dyskinesia, dystonia, and akathisia, necessitating limited duration of use to avoid complications.

Pharmacokinetics

Metoclopramide is rapidly absorbed following oral administration, with peak plasma concentrations occurring within 1 to 2 hours. It is primarily eliminated by the kidneys, and its half-life is approximately 5 to 6 hours. The drug undergoes hepatic metabolism, and its clearance can be affected by renal function.

Contra-indications

• Hypersensitivity to metoclopramide or any of its excipients
• Pheochromocytoma
• Gastrointestinal obstruction, perforation, or hemorrhage
• History of tardive dyskinesia
• Severe renal impairment

Adverse effects

• Drowsiness
• Fatigue
• Restlessness
• Extrapyramidal symptoms
• Tardive dyskinesia
• Diarrhea
• Nausea
• Headache

Interactions

• Antipsychotic medications may enhance the risk of extrapyramidal side effects
• CNS depressants may have additive effects leading to increased sedation
• The absorption of some drugs may be affected due to increased gastrointestinal motility

Precautions

• Use with caution in patients with a history of seizures
• Monitor patients for signs of tardive dyskinesia
• Caution in patients with cardiac disorders due to potential changes in cardiac rhythm

Pregnancy

Metoclopramide should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Consult relevant guidelines for specific recommendations.

Breast-feeding

Metoclopramide is excreted in breast milk. Caution should be exercised when administered to nursing women, and it should only be used if the benefits outweigh the risks.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Formulations

• Tablets: 10 mg
• Oral solution: 5 mg/5 mL
• Injection: 10 mg/2 mL

Mechanism of action

Metoclopramide causes antiemetic effects by inhibiting dopamine D2 and serotonin 5-HT3 receptors in the chemoreceptor trigger zone (CTZ) located in the area postrema of the brain. Administration of this drug leads to prokinetic effects via inhibitory actions on presynaptic and postsynaptic D2 receptors, agonism of serotonin 5-HT4 receptors, and antagonism of muscarinic receptor inhibition. This action enhances the release of acetylcholine, causing increased lower esophageal sphincter (LES) and gastric tone, accelerating gastric emptying and transit through the gut. Metoclopramide antagonizes the dopamine D2 receptors. Dopamine exerts relaxant effect on the gastrointestinal tract through binding to muscular D2 receptors. Metoclopramide accelerates gastric emptying and intestinal transit from the duodenum to the ileocecal valve by increasing the amplitude and duration of esophageal contractions, the resting tone of the lower esophageal sphincter, and the amplitude and tone of gastric (especially antral) contractions and by relaxing the pyloric sphincter and the duodenal bulb, while increasing peristalsis of the duodenum and jejunum. Unlike nonspecific cholinergic-like stimulation of upper GI smooth muscle, the stimulant effects of metoclopramide on GI smooth muscle coordinate gastric, pyloric, and duodenal motor activity. The pharmacologic actions of metoclopramide on the upper GI tract are similar to those of cholinergic drugs (e.g., bethanechol); however, unlike cholinergic drugs, metoclopramide does not stimulate gastric, biliary, or pancreatic secretions and does not affect serum gastrin concentration. Although the exact mechanism of action of metoclopramide is unclear, the effects of metoclopramide on GI motility may be mediated via enhancement of cholinergic excitatory processes at the postganglionic neuromuscular junction; antagonism of nonadrenergic, noncholinergic inhibitory motor nerves (i.e., dopaminergic); and/or a direct effect on smooth muscle. The effects of metoclopramide on GI motility do not depend on intact vagal innervations but are reduced or abolished by anticholinergic drugs (e.g., atropine) and potentiated by cholinergic drugs (e.g., carbachol, methacholine). These findings suggest that metoclopramide's effects on GI motility may depend in part on intramural cholinergic neurons of smooth muscle that are intact after vagal denervation. Unlike cholinergic drugs, metoclopramide requires intrinsic neuronal storage sites of acetylcholine to exert its pharmacologic effects. Postsynaptic activity results from metoclopramide's ability to enhance release of acetylcholine from postganglionic cholinergic neurons in the GI tract and to sensitize muscarinic receptors of GI smooth muscle to the actions of acetylcholine. Metoclopramide is a potent dopamine-receptor antagonist, and some of the actions of metoclopramide on GI smooth muscle may be mediated via antagonism of dopaminergic neurotransmission, Specific dopamine receptors in the esophagus and stomach have been identified; however, it is not known if there is a dopaminergic control system for smooth muscle function in the upper GI tract. In the GI tract, dopamine is principally an inhibitory neurotransmitter. Dopamine decreases the intensity of esophageal contractions, relaxes the proximal stomach, and reduces gastric secretion. Although metoclopramide blocks these inhibitory effects of dopamine, the actual role of dopamine in the peripheral control of GI motility has not been fully elucidated. Since cholinergic mechanisms are responsible for most excitatory motor activity in the GI tract, it appears that metoclopramide's therapeutic effects are principally caused by the drug's cholinergic-like activity; however, antagonism of GI dopaminergic activity may augment metoclopramide's cholinergic-like activity. For more Mechanism of Action (Complete) data for Metoclopramide (10 total), please visit the HSDB record page.

Pharmacodynamics

Metoclopramide increases gastric emptying by decreasing lower esophageal sphincter (LES) pressure. It also exerts effects on the area postrema of the brain, preventing and relieving the symptoms of nausea and vomiting. In addition, this drug increases gastrointestinal motility without increasing biliary, gastric, or pancreatic secretions. Because of its antidopaminergic activity, metoclopramide can cause symptoms of tardive dyskinesia (TD), dystonia, and akathisia, and should therefore not be administered for longer than 12 weeks.