Ondansetron Oral and IV (Zofran®)

Author: Karen Arnold-Korzeniowski, BSN RN
Last Reviewed: January 25, 2024

Pronounce: on-DAN-se-tron

Classification: Antiemetic, Selective 5-HT3 Receptor Antagonist

About: Ondansetron Oral and IV (Zofran®)

Ondansetron is a selective 5-HT3 receptor antagonist. 5-HT3 receptors are found on areas of nerves in the brain and stomach that can trigger a vomiting reflex. Ondansetron stops this reflex and helps prevent and manage nausea and vomiting.

How to Take Ondansetron

Ondansetron can be given on as needed or scheduled basis and should be taken as prescribed by your provider. How you should take your ondansetron and your dosage will depend on the cancer treatments you are receiving. If it is being given along with a chemotherapy regimen, it should be given at least 30 minutes prior to the administration of the chemotherapy. If you are taking ondansetron related to side effects of radiation you should take the medication 1 to 2 hours prior to your treatment. If taking the disintegrating tablet do not push the tablet through the foil backing, rather peel back the foil and gently remove the tablet. Immediately place the tablet on top of the tongue to dissolve. After the tablet has dissolved swallow the saliva in your mouth.

Be sure to tell your healthcare provider about all medications and supplements you take.

This medication, when taken with apomorphine, can cause low blood pressure that can lead to fainting.

Taking this medication with serotonergic medications (often used to treat migraines and depression) can lead to serotonin syndrome. Symptoms of serotonin syndrome that you should notify your provider of include changes in your mental status (agitation, hallucinations, coma), your nervous system (change in heart rate or blood pressure, sweating, dizziness) or in how your muscles are working (tremors, trouble walking). You should call your provider if you are having any symptoms of serotonin syndrome.

High oral doses or intravenous doses can also prolong your QTc, which is related to the electrical activity of your heart. Make sure your health care providers are aware of your ondansetron use before you start any other QTc prolonging medications including, but not limited to: chlorpromazine, cisapride, dofetilide, dronedarone, ibutilide, lenvatinib, methadone, quinine, sotalol, vandetanib, vernakalant, and ziprasidone. If you experience any palpitations or feel like your heart is racing, call your provider right away.

Storage and Handling

All oral versions of ondansetron should be stored in the original, labeled container at room temperature. Keep containers out of reach of children and pets.

Where do I get this medication?

Ondansetron is available through retail/mail order pharmacy. Your oncology team will work with your prescription drug plan to identify an in-network retail/mail order pharmacy for medication distribution. You can work with your provider’s office if this medication needs a prior authorization.

Insurance Information

This medication may be covered under your prescription drug plan. Patient assistance may be available to qualifying individuals without prescription drug coverage. Co-pay cards, which reduce the patient co-pay responsibility for eligible commercially (non-government sponsored) insured patients, may also be available. Your care team can help you find these resources, if they are available.

Possible Side Effects of Ondansetron

This medication is given to manage and/or prevent side effects of your cancer treatment. If you are having side effects from this medication you should talk to your team about if this medication is necessary to your treatment or if there are other options to help manage the side effect this medication is treating. These are some of the most common side effects:


There are several things you can do to prevent or relieve constipation. Include fiber in your diet (fruits and vegetables), drink 8-10 glasses of non-alcoholic fluids a day, and keep active. A stool softener once or twice a day may prevent constipation. If you do not have a bowel movement for 2-3 days, you should contact your healthcare team for suggestions to relieve the constipation.


Your doctor or nurse can recommend medication and other strategies to relieve pain.


Your oncology team can recommend medications to relieve diarrhea. Also, try eating low-fiber, bland foods, such as white rice and boiled or baked chicken. Avoid raw fruits, vegetables, whole grain breads, cereals and seeds. Soluble fiber is found in some foods and absorbs fluid, which can help relieve diarrhea. Foods high in soluble fiber include: applesauce, bananas (ripe), canned fruit, orange sections, boiled potatoes, white rice, products made with white flour, oatmeal, cream of rice, cream of wheat, and farina. Drink 8-10 glasses of non-alcoholic, uncaffeinated fluid a day to prevent dehydration.


Fatigue is very common during cancer treatment and is an overwhelming feeling of exhaustion that is not usually relieved by rest. While on cancer treatment, and for a period after, you may need to adjust your schedule to manage fatigue. Plan times to rest during the day and conserve energy for more important activities. Exercise can help combat fatigue; a simple daily walk with a friend can help. Talk to your healthcare team for helpful tips on dealing with this side effect.


This medication may cause dizziness. Remember to slowly arise from a seated position or from lying down. If you are experiencing dizziness you should not drive.

Less common, but important side effects can include:

  • Allergic Reactions:In some cases, patients can have an allergic reaction to this medication. Signs of a reaction can include: fever, chills, rash, or breathing problems. If you notice any changes in how you feel, let your nurse know immediately.
  • Heart Problems: This medication can cause slow or abnormal heartbeats or an abnormal heart rhythm called QT prolongation. Notify your oncology care team right away if you feel abnormal heartbeats or if you feel dizzy or faint.
  • Masking of an Ileus or Bowel Obstruction: An ileus is a lack of movement of the bowels. A bowel obstruction is a blockage of the small or large intestine. If it is a complete obstruction you will have trouble passing gas and stool. A partial blockage can cause diarrhea. Other symptoms include severe belly pain, nausea, and vomiting. If you are having any of these symptoms you should contact your provider. Because ondansetron manages nausea and vomiting and these are possible side effects of a bowel obstruction, an ileus or bowel obstruction could be occurring and overlooked.

Reproductive Concerns

You should consult with your healthcare team prior to becoming pregnant, fathering a child, or breastfeeding while receiving this medication.