Key Takeaways

You can take Zofran up to 3 times a day for 1-2 days after completing your cancer treatment until it is no longer needed.

If you are experiencing nausea and vomiting after surgery or cancer treatment such as chemotherapy and radiation treatment, your doctor may prescribe a medication called ondansetron (brand name: Zofran). You can take Zofran up to 3 times a day for 1-2 days after completing your cancer treatment until it is no longer needed. Make sure to adhere to the Zofran schedule prescribed by your doctor and take this medication regularly to get maximum benefits.

Please continue reading to learn more about Zofran, including its uses, dosage, and frequency of use. We will also talk about how it works for the prevention of nausea and vomiting, whether it is safe to use during pregnancy, potential drug interactions, and tips on safe Zofran use.

What is ondansetron (Zofran)?

Ondansetron (Zofran, Zofran ODT) is a prescription medication used to prevent nausea and vomiting for cancer patients after chemotherapy and radiation treatment. It is also used to treat nausea after surgery. There may be additional uses of ondansetron (Zofran)—your doctor or pharmacist can give you further information.

Zofran is available in various dosage forms, including oral tablets (4 mg, 8 mg, and 24 mg), orally disintegrating tablets and oral films (4 mg and 8 mg), an oral solution (4 mg/5 mL), and injection vials (2 mg/mL).

Dosage forms such as the orally disintegrating tablet, the oral liquid, and the oral film may cause less of a nauseating feeling than that caused by swallowing a tablet.

How does Zofran work?

Zofran is an antiemetic that belongs to a group of drugs called 5-HT3 receptor antagonists. It works by blocking the action of serotonin, a natural substance in the body that can trigger nausea and initiate a vomiting reflex.

What is the usual dose of Zofran?

The usual dose of ondansetron (Zofran) in adults and children is as follows:

Adults

Severe nausea and vomiting due to chemotherapy: a single 24-mg dose to be taken 30 minutes before the start of a single day of highly emetogenic (vomiting-inducing) chemotherapy.
Moderate nausea and vomiting due to chemotherapy: An 8-mg tablet is administered 30 minutes before the start of chemotherapy, followed by another 8-mg dose 8 hours later. After the completion of chemotherapy, 8 mg of Zofran should be taken every 12 hours for 1 to 2 days.
Radiation therapy: An 8-mg ondansetron is taken 1-2 hours before radiation therapy. After the first dose, the regimen of 8 mg every 8 hours is recommended depending on the type and the location of radiation.
Post-operative (after-surgery) nausea and vomiting: 16 mg of ondansetron is to be administered 1 hour before anesthesia.

Children:

Age 4 to 11: For moderate nausea and vomiting due to chemotherapy, take 4 mg of ondansetron (Zofran) 30 minutes before the start of chemotherapy, followed by another 4 mg dose given at 4 and 8 hours after the first dose. After the completion of chemotherapy, take 4 mg of ondansetron (Zofran) every 8 hours for 1 to 2 days.
Age 12 to 17: For moderate nausea and vomiting due to chemotherapy, take 8 mg of ondansetron (Zofran) 30 minutes before the start of chemotherapy, followed by another 8 mg dose given 8 hours after the first dose. After the completion of chemotherapy, take 8 mg of ondansetron (Zofran) every 12 hours for 1 to 2 days.

Precautions:

People with severe liver disease should not take more than 8 mg of ondansetron in a day.
Zofran is not approved by the FDA to be used during pregnancy. However, there are studies that show Zofran’s safety in treating morning sickness during the first trimester. You should discuss with your doctor if you are pregnant or breastfeeding.
Do not give Zofran to children younger than 4 years old.

When can I take Zofran again?

After 4 Hours

In certain instances, Zofran can be administered every 4 hours. For children, a 4 mg or 8 mg dose of Zofran is given 30 minutes before chemotherapy (4 mg for ages 4-11 years and 8 mg for ages 12-17 years). Two subsequent doses are given at 4-hour intervals, followed by a dose every 8 hours for 1-2 days after chemotherapy.

After 6 Hours

The typical adult dose of Zofran is 8 mg every 8-12 hours or 2-3 times a day. You could take it more frequently, such as every 6 hours, if the dose is less than 8 mg. But the total dose should not exceed 8 mg in the specified timeframe. Adhering to the prescribed schedule of Zofran is important. Consult your healthcare provider before making any dosing adjustments if your nausea and vomiting are not controlled.

After 8 Hours

Zofran is limited to every 8 hours because clinical trials have revealed an increased risk of QT prolongation, an abnormality in the heart’s electrical system. The risk of QT prolongation is dose-related. Doctors avoid intravenous (IV) doses above 16 mg and oral Zofran intake is limited to every 8 hours at home for this reason.

What are the risks associated with Zofran use?

Severe allergic reactions

In a small number of people, Zofran can cause severe allergic reactions with difficulty breathing, swelling of the throat, skin rash, hives, and itching. Stop taking ondansetron (Zofran) and seek immediate medical attention if you develop signs and symptoms of an allergic reaction.

Serotonin syndrome

Excessive ondansetron (Zofran) intake can lead to serotonin syndrome, a potentially life-threatening condition caused by elevated serotonin levels in the body. The risk is higher when Zofran is combined with other medications that also affect serotonin levels, such as lithium, antidepressants, and migraine medications. Symptoms of serotonin syndrome include sweating, fast heartbeat, nausea and vomiting, muscle spasms, muscle stiffness, blurred vision, confusion, and fever. Seek emergency medical attention if you develop these symptoms while on Zofran.

Heart rhythm problems

High doses of ondansetron (Zofran) can increase the risk of heart rhythm problems (arrhythmias), especially in people with congenital long QT syndrome, a history of QT prolongation, congestive heart failure, low potassium or magnesium, and patients taking other drugs that can cause heart rhythm problems. Tell your healthcare provider if you have any heart rhythm abnormalities before starting ondansetron. Call your doctor without delay if you develop chest pain or a fast heartbeat, slow heartbeat, or irregular heartbeat.

Masking of intestinal blockage symptoms

Taking ondansetron to treat nausea and vomiting after abdominal surgery or chemotherapy can mask the symptoms of intestinal blockage and abdominal bloating. Tell your healthcare provider if you are not passing gas or stools. Check out our blog, “13 Common Chemotherapy Side Effects.”

Risk in people with phenylketonuria

People with a rare disorder called phenylketonuria cannot break down an amino acid called phenylalanine. High levels of phenylalanine in the body can cause serious health problems. The orally disintegrating tablet of ondansetron (Zofran ODT) contains phenylalanine. Do not take Zofran ODT if you have phenylketonuria (PKU).

Tips on the safe use of ondansetron (Zofran)

Give your doctor or pharmacist a complete list of your medications, including prescription drugs, over-the-counter medicines, dietary supplements, and herbal remedies. This can help avoid dangerous drug interactions between ondansetron and another prescription medication or OTC product.
You can take ondansetron with or without food.
If you are taking the disintegrating tablet of Zofran, remove the foil backing with dry hands and immediately place the tablet under your tongue.
Besides common side effects of ondansetron, like headache, tiredness, diarrhea, and constipation, this medicine can also cause dizziness. Do not drive or operate machinery until you know how ondansetron affects you. Drinking alcohol can make these side effects worse.
In case of a missed dose, take your Zofran dose as soon as you remember. If it is time for the next dose, skip the missed dose and take the next dose according to the prescribed schedule. Do not take two doses to make up for a missed dose.

Learn more about nausea remedies. Check out our blog “What Are the Best Medications for Nausea?”

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