Introduction
Diabetic gastroparesis is a condition that causes frequent nausea and vomiting, which has a negative impact on quality of life and poses a significant burden on the healthcare system. Metoclopramide is a dopamine antagonist used to treat nausea and vomiting that may be associated with diabetic gastroparesis in addition to gastroesophageal reflux disease (GERD). It can also be used to prevent nausea or vomiting associated with chemotherapy or certain surgical or diagnostic procedures.
One unique property of this drug is that it does not increase gastric acid secretion. It is available in the oral tablet form or in solution, and can also be administered through the intravenous route. Metoclopramide was initially approved by the FDA in 1980.
Uses
Metoclopramide is an antiemetic agent and dopamine D2 antagonist used in the treatment of gastroesophageal reflux disease, prevention of nausea and vomiting, and to stimulate gastric emptying.
Metoclopramide in the oral tablet form is used for symptomatic treatment of both acute and recurrent diabetic gastroparesis, in addition to the treatment of gastroesophageal reflux disease (GERD) in patients who have failed to respond to traditional therapy. A nasal spray formulation is also indicated to treat adults with acute, recurrent diabetic gastroparesis.
In the intravenous injection form, it is indicated for the above conditions as well as for the prevention of vomiting that may follow emetogenic chemotherapy or nausea and vomiting after surgery. Intravenous metoclopramide facilitates intubation of the small bowel and stimulates gastric emptying and barium flow in patients who require radiological examination of the stomach or small intestine. In some cases, the delay of gastrointestinal emptying interferes with the radiographic visualization of the gastrointestinal tract, and metoclopramide is used to facilitate emptying in these cases, allowing for adequate diagnostic visualization.
Some off-label uses of metoclopramide include the management of radiation-induced nausea and vomiting, gastric bezoars, intractable hiccups, and migraine pain.
Associated Conditions
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.
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.
Absorption
Metoclopramide is rapidly absorbed in the gastrointestinal tract with an absorption rate of about 84%. The bioavailability of the oral preparation is reported to be about 40.7%, but can range from 30-100%.
Nasal metoclopramide is 47% bioavailable. A 15mg dose reaches a Cmax of 41.0 ng/mL, with a Tmax of 1.25 h, and an AUC of 367 ng*h/mL.
Volume of Distribution
The volume of distribution of metoclopramide is approximately 3.5 L/kg. This implies a high level of tissue distribution. Metoclopramide crosses the placental barrier and can cause extrapyramidal symptoms in the fetus.
Protein Binding
Metoclopramide is 30% bound to plasma proteins, mainly to alpha-1-acid glycoprotein.
Route of Elimination
About 85% of an orally administered dose was measured in the urine within 72 hours during a pharmacokinetic study. An average of 18% to 22% of 10-20 mg dose was recovered as free drug within 3 days of administration.
Half Life
The mean elimination half-life of metoclopramide in people with healthy renal function ranges from 5 to 6 hours but is prolonged in patients with renal impairment. Downward dose adjustment should be considered.
Clearance
The renal clearance of metoclopramide is 0.16 L/h/kg with a total clearance of 0.7 L/h/kg. Clinical studies showed that the clearance of metoclopramide may be reduced by up to 50% in patients with renal impairment. After high intravenous doses, total metoclopramide clearance ranged from 0.31 to 0.69 L/kg/h.
Toxicity
The rat oral LD50 of metoclopramide is 750 mg/kg.
Some symptoms of an overdose with metoclopramide include drowsiness, disorientation, and extrapyramidal reactions. Drugs that manage Parkinson's disease or anticholinergic drugs or antihistamines with anticholinergic properties should be employed to treat extrapyramidal symptoms. Normally, these symptoms subside within 24 hours. Unintentional overdose in infants receiving the oral solution of metoclopramide resulted in seizures, extrapyramidal symptoms, in addition to a lethargic state.
In addition, methemoglobinemia has been found to occur in premature and full-term neonates after a metoclopramide overdose. Intravenous methylene blue may treat metoclopramide-associated methemoglobinemia. It is important to note that methylene blue administration may lead to hemolytic anemia in patients who suffer from G6PD deficiency, which can result in fatality. Dialysis has not been shown to be effective in sufficiently eliminating metoclopramide in an overdose situation due to low plasma distribution of this drug.
Food Interactions
- Avoid alcohol.
- Take before a meal. Co-administration with food decreases bioavailability - take 30 minutes before meals.
Dosage
Adults less than 65 years of age: The recommended dosage is 1 spray (15 mg) in one nostril, 30 minutes before each meal and at bedtime (maximum of 4 sprays daily) for 2 to 8 weeks, depending on symptomatic response.
Adults 65 years of age and older: Metoclopramide is not recommended in geriatric patients as initial therapy. Geriatric patients receiving an alternative metoclopramide product at a stable dosage of 10 mg four times daily can be switched to Metoclopramide 1 spray (15 mg) in one nostril, 30 minutes before each meal and at bedtime (maximum four times daily) for 2 to 8 weeks, depending on symptomatic response.
Metoclopramide tablet:
Gastroesophageal Reflux: Administer Metoclopramide continuously or intermittently:
- Continuous: Administer 10 to 15 mg, 30 minutes before each meal and at bedtime (maximum of 60 mg per day) for 4 to 12 weeks.
- Intermittent: Single doses up to 20 mg prior to provoking situation.
Metoclopramide injection:
For the Relief of Symptoms Associated with Diabetic Gastroparesis (Diabetic Gastric Stasis): If only the earliest manifestations of diabetic gastric stasis are present, oral administration of metoclopramide may be initiated. However, if severe symptoms are present, therapy should begin with Metoclopramide Injection (IM or IV). Doses of 10 mg may be administered slowly by the intravenous route over a 1- to 2-minute period. Administration of Metoclopramide Injection (metoclopramide injection, USP) up to 10 days may be required before symptoms subside, at which time oral administration of metoclopramide may be instituted. The physician should make a thorough assessment of the risks and benefits prior to prescribing further metoclopramide treatment.
For the Prevention of Nausea and Vomiting Associated with Emetogenic Cancer Chemotherapy: Intravenous infusions should be made slowly over a period of not less than 15 minutes, 30 minutes before beginning cancer chemotherapy and repeated every 2 hours for two doses, then every 3 hours for three doses. The initial two doses should be 2 mg/kg if highly emetogenic drugs such as cisplatin or dacarbazine are used alone or in combination. For less emetogenic regimens, 1 mg/kg per dose may be adequate.
For the Prevention of Postoperative Nausea and Vomiting: Metoclopramide Injection should be given intramuscularly near the end of surgery. The usual adult dose is 10 mg; however, doses of 20 mg may be used.
