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Treatment Name: Ondansetron (Zofran®, Zofran ODT®)

Ondansetron (Zofran®, Zofran ODT®) is a Supportive Care Therapy to prevent or treat Nausea and Vomiting

How does ondansetron work?
Ondansetron (Zofran®) is designed to block receptors in your body that control nausea and vomiting. These are called “serotonin type” (5-HT) receptors. 5-HT3 is a specific serotonin receptor that is located mostly in your brain, nervous system, and intestines (gut). When serotonin is released in the gut and brain, the body triggers vomiting. Ondansetron (Zofran®) binds to 5HT3 receptors instead of serotonin, and thereby stops the reflex to vomit.

Goals of therapy:
Ondansetron is given by mouth or IV (in the vein, intravenously) to both prevent and treat nausea and vomiting from chemotherapy, or other causes of nausea. Ondansetron is commonly taken on a scheduled basis just before chemotherapy and on an as needed basis at home. When a medicine is taken to prevent nausea and vomiting, it is known as prophylaxis, or prophylactic therapy.


Ondansetron is usually given in an outpatient infusion center before chemotherapy to prevent nausea and vomiting. Ondansetron may also be taken at home for breakthrough nausea or vomiting.

  • Usual ondansetron starting dose just before chemotherapy:
    • Range: 4 to 16 mg slow IV push over 2 - 5 minutes, at least 30 minutes before chemotherapy
    • Range: 4 to 24 mg by mouth, at least 30 minutes before chemotherapy

  • Usual ondansetron starting dose at home:
    • 4 mg oral (tablet) by mouth every 6 hours as needed
    • 8 mg oral (tablet) by mouth every 8 hours as needed

The ondansetron dosage will depend upon the exact chemotherapy agents you are taking or receiving. Higher doses may be used for chemotherapy regimens with greater rates of nausea or vomiting, but know that higher doses may also lead to more side effects (shown below).

After chemotherapy, ondansetron is commonly taken at home. Typical duration of therapy is until ondansetron no longer works in relieving nausea and vomiting or nausea has resolved and ondansetron is no longer needed.

Side Effects

In the ondansetron prescribing label information (Zofran®, Zofran ODT® package insert), the most commonly reported ondansetron (Zofran®, Zofran ODT®) side effects are shown here. The exact percentages of patients that will experience ondansetron side effects is unknown because it has been used under widely varying patient populations in a variety of clinical trials:

  • Headache (more than or equal to 5%)
  • Fatigue (more than or equal to 5%)
  • Constipation (more than or equal to 5%)
  • Diarrhea (more than or equal to 5%)

Rare [less than 1%]:

  • Extrapyramidal reactions (Muscle spasms, shakiness, and issues with moving or speaking)
  • Liver enzyme elevation
  • Rash
  • Serious unsafe heart rhythms
  • Serious allergic reactions

Important note: If you have these side effects from ondansetron, ask your doctor or pharmacist if decreasing the dose or frequency (the number of times per day) might help.

Side effect videos Side Effect Videos
Nausea and VomitingNausea and VomitingFatigue Fatigue ConstipationConstipationDiarrheaDiarrhea


How often is monitoring needed?
Labs (blood tests) will usually be checked on the day of chemotherapy. They may also be checked as needed if you are having trouble with nutrition, hydration, or electrolyte levels due to nausea and vomiting. Labs often include: Comprehensive Metabolic Panel (CMP), Magnesium, Phosphate, plus any others your doctor may order.

How might test results/imaging affect treatment?
In those with low potassium or low magnesium, heart failure, or slow heart rhythm, it may be recommended that ECG monitoring be done to determine the QTc interval and to make sure the time to make a heart beat is not too long. An ECG (or “EKG”) may also be needed if you are taking medicines that may prolong the QTc interval. Heart rhythm changes from ondansetron occur in a dose-dependent manner, but are rare and occurr mainly with I.V., rather than oral ondansetron.

In patients with severe liver impairment, the maximum daily dose of ondansetron is 8 mg because ondansetron is metabolized by the liver.

ChemoExperts Tips

  • Although ondansetron is often the first choice to prevent or treat nausea and vomiting at home, it is important that the cause is identified because sometimes ondansetron does not work for certain causes of nausea. Ondansetron is non-drowsy for most people that take it, making it useful anti-nausea option during daytime hours.
  • A common side effect with ondansetron (Zofran®) is headache. Those with a history of migraines may be at higher risk of headaches from ondansetron. If your headaches noticeably worsen shortly after taking ondansetron, contact your doctor to see if other anti-nausea medicines with a lower risk of headache may be better for you to use
  • Another common side effect of ondansetron (Zofran®) is constipation. Constipation can have many causes including a diet low in fiber, certain types of chemotherapy, recent abdominal surgery, or use of pain medicines. It is important to have a bowel movement at least every other day. Otherwise, your small bowel may become blocked. Over-the-counter laxatives and stimulants can help. Work with your doctor on a plan to keep your bowel movements regular
  • Swallowing tablets may be too difficult in cases of severe nausea or vomiting. If you feel like you cannot keep ondansetron tablets down, ask your doctor if they can prescribe the orally dissolving tablet (ODT) form of ondansetron. This form of ondansetron dissolves on the tongue, or inside the cheek and does not need liquid for swallowing
  • If you are given palonosetron (Aloxi®) before your chemotherapy, do not take ondansetron at home for 3 days (72 hours) after your infusion. Palonosetron is a long-acting drug given I.V. (in the vein) that works in a similar way to ondansetron. It lasts for about 3 days in the body. Taking ondansetron during this time may cause more side effects, without helping with nausea
  • It is unknown if ondansetron will harm a developing baby. Ondansetron should be used in pregnant women only if the potential benefits to the mother outweighs the potential risks to the unborn baby
  • A pharmacist should ALWAYS review your medication list to ensure that drug interactions are prevented or managed appropriately

Patient Assistance & Co-payment Coverage

Patients under the age of 65 years, or those with private insurance plans:
If you have insurance and are looking for patient assistance or copay assistance for Ondansetron (Zofran®, Zofran ODT®), we have provided links that may help.

Visit our Patient Assistance page and click the links to various patient assistance programs for help paying for Ondansetron (Zofran®, Zofran ODT®). Depending upon your income, they may be able to help cover the cost of:

  • Ondansetron (Zofran®, Zofran ODT®)

For Branded medications (may be available for generic medications too), check with the manufacturer to determine if a co-pay card is offered and if it could reduce your monthly copay.

  • If you are uninsured, check with the manufacturer to determine if you are eligible to receive medication at no cost.

Medicare and Medicaid patients (Patients 65 years or older):
The clinic providing treatment will likely pre-authorize medications and immune therapies such as Ondansetron (Zofran®, Zofran ODT®) and are the best source to help you understand drug cost.

  • Ask to speak with a patient assistance technician or financial counselor at the clinic or hospital administering this therapy.

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1) Zofran® injectable package insert

2) Zofran® oral, Zofran ODT® package insert

Created: May 6, 2017 Updated: May 6, 2017

What is Nausea and Vomiting?

Nausea is the sensation that there is a need to vomit. Nausea can be acute and short-lived, or it can be prolonged. When prolonged, it is a debilitating symptom. Nausea (and vomiting) can be psychological or physical in origin.

NOTE: Treatment Options listed below are not all-inclusive. Other treatments may be available. ChemoExperts provides drug information and does not recommend any one treatment over another. Only your Doctor can choose which therapy is appropriate for you.

What is 5HT?

5-HT is an abbreviation for 5-hydroxytryptamine, which is also known as serotonin

What are electrolytes?

Electrolytes are basic elements that the body needs to do things like make the heart beat and contract muscles. If you are not drinking or eating well due to nausea and vomiting, electrolyte levels may be too low or too high in your blood. 

The major electrolytes include: sodium, chloride, potassium, calcium, magnesium, and phosphate. These electrolytes are watched closely during your care to make sure they stay at safe levels.

What is a CMP?

A Comprehensive Metabolic Panel (CMP) is a frequently ordered blood test that tells clinicians the status of your: 1) Electrolytes & Acid/Base status2) Kidney function, 3) Liver function, 4) Blood sugar, and 5) Calcium at the time the test was taken. It is commonly used to monitor liver and kidney function when beginning new medications such as chemotherapy. A total of 14 tests are run simultaneously and are shown below.

Electrolytes & Acid/Base status:
1) Sodium, 2) Potassium, 3) Carbon dioxide, 4) Chloride

Kidney Function:
5) BUN (blood urea nitrogen), 6) Serum creatinine (Scr)

Liver Function:
7) AST, 8) ALT, 9) Total bilirubin, 10) Alk Phos, 11) Albumin, 12) Total protein

Blood sugar:
13) Serum glucose

14) Serum calcium

What is the QTc interval?

The time it takes your heart to make one beat can be measured using an electrocardiogram (ECG, or EKG) and is reported as the QTc interval. Ondansetron is generally safe to give when the QTc interval for men is less than 450 milliseconds per beat, and for women, less than 460 milliseconds per beat.

The QTc interval is prolonged if the heart takes too long to make the next beat, and could lead to a dangerous heartbeat known as an arrhythmia.

Certain medications, in addition to ondansetron, may prolong the QTc interval. The list includes: Levofloxacin or ciprofloxacin antibiotics, certain oral chemotherapy medications, and others. Make sure your pharmacist checks all new medications to make sure they do not prolong the QTc interval.

Causes of nausea (other than chemotherapy)

  • Dehydration​
  • Motion sickness
  • Swelling in brain
  • Anxiety or anticipatory nausea
  • Delayed emptying of stomach contents, such as in gastrointestinal obstruction or gastroparesis
  • Nausea from pain medication or other medicines (if allowed, taking these medications with food may help)