Ondansetrón: Uses, How it works, Dosage, Side Effects, Interaction

Ondansetrón commonly known by the brand name Zofran among others is a medication used to prevent nausea and vomiting caused by cancer chemotherapy, radiation therapy, or surgery. It is also effective for treating gastroenteritis. It can be given by mouth or by injection into a muscle or into a vein. Ondansetrón was patented in 1984 and approved for medical use in 1990.  It is on the World Health Organization’s List of Essential Medicines. It is available as a generic medication. In 2019, it was the 60th most commonly prescribed medication in the United States, with more than 11 million prescriptions.

How Ondansetrón works

Ondansetrón is in a class of medications called serotonin 5-HT3 receptor antagonists. It works by blocking the action of serotonin, a natural substance that may cause nausea and vomiting caused by cancer chemotherapy, radiation therapy, and surgery.

How should Ondansetrón be used?

Ondansetrón comes as a tablet, a rapidly disintegrating (dissolving) tablet, film, and an oral solution (liquid) to take by mouth. The first dose of Ondansetrón 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. Additional doses are sometimes taken one to three times a day during chemotherapy or radiation therapy and for 1 to 2 days after the end of treatment. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take Ondansetrón exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor. Do not chew the film.

If you are taking the rapidly disintegrating tablet, remove the tablet from the package just before you take your dose. To open the package, do not try to push the tablet through the foil backing of the blister. Instead, use dry hands to peel back the foil backing. Gently remove the tablet and immediately place the tablet on the top of your tongue. The tablet will dissolve in a few seconds and can be swallowed with saliva.

Ondasetrón injection

Ondansetron also comes as a solution (liquid) to be injected intravenously (into a vein) or intramuscularly (into a muscle) by a health care provider in a hospital or clinic. When ondansetron is used to prevent nausea and vomiting caused by chemotherapy, it is usually given 30 minutes before the start of chemotherapy. Additional doses may be given 4 hours after the first dose of ondansetron and 8 hours after the first dose of ondansetron if needed. When ondansetron is used to prevent nausea and vomiting caused by surgery, it is usually given just before the surgery. Ondansetron is also sometimes given after surgery to patients who are experiencing nausea and vomiting and who did not receive ondansetron before surgery.

What should I do if I forget a dose?

Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. Overdose symptoms may include sudden loss of vision, severe constipation, feeling light-headed, or fainting.

What to avoid

Ondansetrón may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

What side effects can this medication cause?

Ondansetrón may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • chills
  • constipation
  • drowsiness
  • headache
  • tiredness
  • weakness

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately or seek emergency medical treatment:

  • agitation
  • blurred vision or vision loss
  • chest pain
  • coma (loss of consciousness)
  • confusion
  • difficulty breathing or swallowing
  • dizziness, light-headedness, or fainting
  • excessive sweating
  • fast, slow or irregular heartbeat
  • fever
  • hallucinations (seeing things or hearing voices that do not exist)
  • hives
  • hoarseness
  • itching
  • loss of coordination
  • nausea, vomiting, or diarrhea
  • rash
  • seizures
  • shortness of breath
  • stiff or twitching muscles
  • swelling of the eyes, face, lips, tongue, throat, hands, feet, ankles, or lower legs

Ondasetrón may cause other side effects. Call your doctor if you have any unusual problems while you are taking this medication.

What other drugs will affect Ondansetrón?

Ondansetrón can cause a serious heart problem, especially if you use certain medicines at the same time, including antibiotics, antidepressants, heart rhythm medicine, antipsychotic medicines, and medicines to treat cancer, malaria, HIV, or AIDS. Tell your doctor about all medicines you use, and those you start or stop using during your treatment with Ondasetrón.

Taking Ondansetrón while you are using certain other medicines can cause high levels of serotonin to build up in your body, a condition called “serotonin syndrome,” which can be fatal. Tell your doctor if you also use:

•          medicine to treat depression;

•          medicine to treat a psychiatric disorder;

•          a narcotic (opioid) medication; or

•          medicine to prevent nausea and vomiting.

This list is not complete and many other drugs can interact with Ondansetrón. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.


Dr. Oche Otorkpa PG Cert, MPH, PhD

Dr. Oche is a seasoned Public Health specialist who holds a post graduate certificate in Pharmacology and Therapeutics, an MPH, and a PhD both from Texila American University. He is a member of the International Society of Substance Use Professionals and a Fellow of the Royal Society for Public Health in the UK. He authored two books: "The Unseen Terrorist," published by AuthorHouse UK, and "The Night Before I Killed Addiction."
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