Ondansetron (Zofran) vs. meclizine

• Ondansetron and meclizine are used to prevent nausea and vomiting.
• Ondansetron is mainly used to prevent nausea and vomiting caused by cancer chemotherapy and to prevent vomiting and nausea after surgery.
• Meclizine is also used to treat and prevent vertigo, dizziness, and motion sickness.
• Brand names for ondansetron include Zofran, Zofran ODT, and Zuplenz.
• Brand names for meclizine include Bonine, Medi-Meclizine, and Verticalm.
• Ondansetron and meclizine belong to different drug classes. Ondansetron is an anti-nausea medication and meclizine is an antihistamine with antiemetic (anti-nausea) and antispasmodic (anti-muscle spasm) activity.
• Side effects of ondansetron and meclizine that are similar include drowsiness, constipation, diarrhea, and abnormal heart rate.
• Side effects of ondansetron that are different from meclizine include headache, feeling unwell (malaise), fatigue, dizziness, and abnormal heart rhythm.
• Side effects of meclizine that are different from ondansetron include nausea, dry mouth, blurred vision, rash, urinary retention, and low blood pressure (hypotension).

Ondansetron is an anti-nausea medication most often used to prevent nausea and vomiting caused by cancer chemotherapy. Chemotherapy drugs increase secretion of serotonin that stimulates serotonin (5-HT3) receptors in the brain, causing nausea and vomiting. Ondansetron works by selectively blocking serotonin (5-HT3) receptors, reducing the effect of increased serotonin due to chemotherapy. Ondansetron is also used to prevent nausea and vomiting after surgery.

Meclizine is an antihistamine with antiemetic (anti-nausea) and antispasmodic (anti-muscle spasm) activity used to treat and prevent vertigo, dizziness, vomiting, nausea, and motion sickness. It also suppresses the nervous system by blocking the action of the neurotransmitter acetylcholine. Meclizine prevents nausea and vomiting by reducing the activity of the center in the brain that controls nausea. It also prevents motion sickness by reducing excitability of neurons in the motion and balance center (vestibular region) of the brain.

Ondansetron

Side effects of ondansetron are

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

Some individuals may develop abnormal heart rate and rhythm.

Meclizine

Meclizine can cause drowsiness. Other side effects include:

• nausea,
• dry mouth,
• blurred vision,
• rash,
• constipation,
• diarrhea and
• urinary retention (inability or difficulty urinating).

Meclizine also has been associated with hypotension (low blood pressure) and heart palpitations.

Ondansetron

Dosage 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.

Dosage 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.

Meclizine

When used for treating symptoms of motion sickness, meclizine 12.5-50 mg should be taken one hour prior to travel and then every 24 hours for the duration of the journey. The dosing should not exceed 50 mg in 24 hours. Vertigo is treated with 25-100 mg daily in a single dose or in 4 divided doses.

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.

Meclizine

Alcohol, sedatives, and tranquilizers can increase drowsiness caused by meclizine. Combining meclizine with pramlintide (Symlin) increases the effect of both drugs on slowing bowel movement.

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 to be cautious before using it in nursing mothers.

Meclizine

Available information suggests that the risk of harm to the baby is minimal when meclizine is used while breastfeeding.