Ondansetron

Ondansetron is a prescription medication used to prevent nausea and vomiting caused by chemotherapy or surgery. Ondansetron belongs to a group of drugs called serotonin 5-HT3 antagonists, which block serotonin, a natural chemical in the body, from causing nausea and vomiting.

This medication comes in several oral forms: tablets, orally disintegrating (dissolving) tablets, an oral soluble film, and solution (liquid). Ondansetron is also available in an injectable form to be given directly into a vein (IV) by a healthcare professional.

The first oral dose of ondansetron is usually taken 30 minutes before the start of chemotherapy, 1 to 2 hours before the start of radiation therapy, or 1 hour before surgery.

Common side effects include headache, tiredness, and constipation. Ondansetron can cause dizziness. Do not drive or operate heavy machinery until you know how it affects you.

Ondansetron is a prescription medication used for the:

• prevention of nausea and vomiting associated with chemotherapy
• prevention of nausea and vomiting caused by radiation therapy
• prevention of nausea and vomiting caused by surgery 

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.

Ondansetron may be found in some form under the following brand names:

• Zofran

• Zofran ODT

• Zuplenz

Ondansetron can cause serious side effects. See "Drug Precautions" section.

Common side effects include:

• headache
• tiredness
• constipation
• diarrhea
• dizziness

This is not a complete list of ondansetron side effects. Ask your doctor or pharmacist for more information.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

• apomorphine (Apokyn)
• medications for irregular heart beat
• carbamazepine (Carbatrol, Epitol, Equetro, Tegretol)
• phenytoin (Dilantin, Phenytek)
• rifampicin (Rifadin)
• tramadol (Rybix, Rybix ODT, Ultram, Ultram ER)

This is not a complete list of ondansetron drug interactions. Ask your doctor or pharmacist for more information.

Serious side effects have been reported with ondansetron including:

Do not take ondansetron if you:

• are allergic to ondansetron or any ingredient in it
• are taking apomorphine (Apokyn)
• have long QT syndrome (condition that increases the risk of developing an irregular heartbeat that may cause fainting or sudden death)

Ondansetron can cause drowsiness. Do not drive or operate heavy machinery until you know how ondansetron affects you.

Medications can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of ondansetron, there are no specific foods that you must exclude from your diet when receiving this medication.

Before taking ondansetron, tell your doctor about all of your medical conditions. Especially tell your doctor if you:

• or anyone in your family has or has ever had long QT syndrome (condition that increases the risk of developing an irregular heartbeat that may cause fainting or sudden death)
• have heart disease
• have liver disease
• have an electrolyte imbalance
• have phenylketonuria (PKU). PKU is an inherited condition in which a special diet must be followed to prevent mental retardation. The orally disintegrating tablets (ondansetron ODT) contain aspartame that forms phenylalanine.
• are pregnant or breastfeeding

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

Ondansetron falls into category B. There are no good studies that have been done in humans with ondansetron. But in animal studies, pregnant animals were given this medication, and the babies did not show any medical issues related to this medication.

It is not known if ondansetron crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. Your doctor and you will decide if the benefits outweigh the risk of using ondansetron.

• The first oral dose of ondansetron is usually taken 30 minutes before the start of chemotherapy, 1 to 2 hours before the start of radiation therapy, or 1 hour before surgery.
• Your ondansetron dosage can be taken with or without food. 
• The orally disintegrating tablets (ondansetron ODT) can be taken without water (they dissolve in your mouth).
• For ondansetron orally disintegrating tablets (ODTs), you should keep each tablet in its original blister pack until you need it. Do not try to push the tablet through the foil (the tablet is delicate and would be crushed). Instead, gently peel the foil away and remove the tablet.
• IMMEDIATELY place the Zofran ODT Tablet on top of the tongue where it will dissolve in seconds, then swallow with saliva. Administration with liquid is not necessary.
• If you miss a dose of ondansetron, take your next dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose of ondansetron.

Take ondansetron exactly as prescribed by your doctor. Follow the directions on your prescription label carefully.

Surgery

The recommended ondansetron dose for preventing nausea and vomiting after surgery is 16 mg taken one hour before anesthesia is administered.

Chemotherapy

High-risk (for nausea and vomiting) chemotherapy: The dose of ondansetron for high-risk chemotherapy is 24 mg 30 minutes before chemotherapy.

Medium-risk (for nausea and vomiting) chemotherapy: The dose of ondansetron for medium-risk chemotherapy is ondansetron 8 mg twice daily.

• The first dose should be taken 30 minutes before chemotherapy.
• The second dose should be taken eight hours after the first dose.
• After that, ondansetron should be taken twice a day (about every 12 hours) until one to two days after chemotherapy.

​Radiation

The recommended oral dosage of ondansetron is one 8 mg given 3 times a day.

Total body irradiation: The dose of ondansetron for total body irradiation is 8 mg taken one to two hours before radiotherapy each day of radiation treatment.

Single high-dose fraction radiotherapy to the abdomen: The recommended dose is 8 mg taken one to two hours before radiotherapy followed by 8 mg every eight hours until one to two days after radiation.

Daily fractionated radiotherapy to the abdomen: The recommended dose is 8 mg taken each day one to two hours before radiotherapy, with subsequent doses every 8 hours after the first dose for each day radiotherapy is given.

Dose in Patients with Liver Disease

The dose of ondansetron is decreased for people who have poor liver function (hepatic function). People with severely impaired liver function should not take more than 8 mg ondansetron total each day.

If you take too much ondansetron, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away.

Keep this and all medications out of the reach of children.