Ondansetron (Zofran) vs. metoclopramide (Reglan)

• Ondansetron and metoclopramide are used to prevent and treat nausea and vomiting.
• Ondansetron is most often used to prevent nausea and vomiting caused by cancer chemotherapy and to prevent vomiting and nausea after surgery.
• Metoclopramide is used to relieve heartburn symptoms with gastroesophageal reflux when certain other treatments do not work and to relieve the symptoms of slow stomach emptying in people with diabetes.
• Brand names for ondansetron include Zofran, Zofran ODT, and Zuplenz.
• Brand names for metoclopramide include Reglan and Metozolv ODT.
• Ondansetron and metoclopramide belong to different drug classes. Ondansetron is an anti-nausea medication and metoclopramide is a "prokinetic" drug.
• Side effects of ondansetron and metoclopramide that are similar include fatigue and drowsiness.
• Side effects of ondansetron that are different from metoclopramide include headache, feeling unwell (malaise), constipation, dizziness, diarrhea, and abnormal heart rate and rhythm.
• Side effects of metoclopramide that are different from ondansetron include restlessness, anxiety, insomnia, depression, and sedation.

Ondansetron is an anti-nausea medication used to prevent nausea and vomiting that results from cancer chemotherapy. Chemotherapy agents cause increased secretion of serotonin, which stimulates serotonin (5-HT3) receptors in the brain, resulting in nausea and vomiting. Ondansetron works by selectively blocking serotonin (5-HT3) receptors, thereby reducing the effect of increased serotonin due to chemotherapy. It is also prescribed for prevention of nausea and vomiting after surgery.

Metoclopramide is a "prokinetic" drug that stimulates the muscles of the gastrointestinal tract including the muscles of the lower esophageal sphincter, stomach, and small intestine by interacting with receptors for acetylcholine and dopamine on gastrointestinal muscles and nerves. It is used in adults to relieve heartburn symptoms with gastroesophageal reflux when certain other treatments do not work and to relieve the symptoms of slow stomach emptying in people with diabetes.

Ondansetron

Side effects of ondansetron are

• headache,
• malaise,
• fatigue,
• drowsiness,
• constipation,
• dizziness, and
• diarrhea.

Some individuals may develop abnormal heart rate and rhythm.

Metoclopramide

Metoclopramide is generally well tolerated when used in low doses for brief periods. Neurological side effects increase with higher doses and longer periods of treatment.

Common side effects of metoclopramide are:

• drowsiness,
• restlessness,
• fatigue,
• anxiety,
• insomnia,
• depression, and
• sedation.

Other important side effects of metoclopramide include serious neurological symptoms that mimic Parkinson's disease such as:

• involuntary muscle movements,
• facial grimacing, and
• dystonic reactions resembling tetanus.

Fortunately, these more serious side effects are infrequent and usually -- though not always -- disappear when metoclopramide is discontinued. Patients with Parkinson's disease can experience worsening of symptoms with metoclopramide. Metoclopramide may impair the mental and/or physical abilities to drive or operate machinery.

Ondansetron

Dosing for adults:

• Highly nauseating chemotherapy: 24 mg orally dissolved on tongue 30 minutes prior to start of a single-day chemotherapy.
• Moderately nauseating chemotherapy: Take 8 mg tablet 30 minutes prior to chemotherapy and repeat in 8 hours, then 8 mg every 12 hours for 1 to 2 days after chemotherapy.
• Radiation-induced nausea and vomiting: Take 8 mg orally 1 to 2 hours prior to radiation and every 8 hours after first dose, as needed.
• Post-surgery nausea and vomiting: 16 mg orally 1 hour before anesthesia.

Dosing for children:

• Moderately nauseating chemotherapy (12 years and older): 8 mg orally prior to chemotherapy and repeat in 8 hours, then 8 mg every 12 hours for 1 to 2 days after chemotherapy.
• Moderately nauseating chemotherapy (4 to 11 years): 4 mg orally 30 minutes prior to chemotherapy and repeat in 4 and 8 hours after the first dose, then every 8 hours for 1 to 2 days after chemotherapy.
• Not recommended for children under 4 years old.

Metoclopramide

The usual dose of metoclopramide for treating GERD is 10-15 mg four times daily, 30 minutes before each meal.

Gastroparesis is treated with 10 mg administered orally four times daily, 30 minutes before each meal and at bedtime.

Ondansetron

Ondansetron and apomorphine should not be used together due to sudden lowering in blood pressure and loss of consciousness.

Phenytoin, carbamazepine, and rifampin can increase ondansetron elimination and decrease blood levels, possibly lowering the effects of ondansetron.

Dronedarone can increase blood levels of ondansetron by reducing its breakdown in the liver. This may increase side effects of ondansetron. This combination may also increase the risk of abnormal heartbeats.

Metoclopramide

Since metoclopramide accelerates emptying of the stomach, it can increase or decrease absorption and effects of other drugs that are absorbed in the small intestine. For example, the effects of alcohol, diazepam (Valium) and cyclosporine can be accelerated when used together with metoclopramide.

Conversely, metoclopramide may decrease the concentrations in blood of digoxin (Lanoxin) and cimetidine (Tagamet).

Metoclopramide should not be used in patients taking MAO inhibitors -- for example, isocarboxazid (Marplan), phenelzine (Nardil), tranylcypromine (Parnate), selegiline (Eldepryl), and procarbazine (Matulane) -- because of the risk of serious adverse effects due to excess release of neurotransmitters.

Concurrent administration of anticholinergic drugs can decrease the effectiveness of metoclopramide.

Ondansetron

There are no adequate studies of ondansetron in pregnant women to determine its safe and effective use during pregnancy.

It is not known whether ondansetron enters breast milk; therefore, it is best for nursing mothers to be cautious before using it.

Metoclopramide

The safety of metoclopramide in pregnancy has not been established.

Metoclopramide is excreted in human breast milk. Nursing mothers should avoid metoclopramide during pregnancy.