Class Name(s):

• 56:22.20 5-HT3 Receptor Antagonists

Pronunciation:

• (on dan' se tron)

Brand Name(s):

• Zofran^® Injection¶; also available generically

WHY is this medicine prescribed?

Ondansetron injection is used to prevent nausea and vomiting caused by cancer chemotherapy and surgery. Ondansetron 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.

HOW should this medicine be used?

Ondansetron 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. Ondansetron is given before chemotherapy or surgery, but may also be given after.

Are there OTHER USES for this medication?

Ondansetron is also sometimes used to help prevent and treat nausea and vomiting during pregnancy or from other causes.

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

What SPECIAL PRECAUTIONS should I follow?

Before using ondansetron,

• tell your doctor or pharmacist if you are allergic to this medication, any part of this medication, or any other medications, foods or substances. Tell your doctor or pharmacist about the allergy and what symptoms you had.
• some medications should not be taken with ondansetron injection. Other medications may cause dosing changes or extra monitoring when taken with ondansetron injection. Make sure you have discussed any medications you are currently taking or plan to take before using ondansetron injection with your doctor and pharmacist. Before starting, stopping, or changing any medications while using ondansetron injection, please get the advice of your doctor or pharmacist.
• tell your doctor if you or anyone in your family has or has ever had long QT syndrome (a rare heart problem that may cause irregular heartbeat, fainting, or sudden death), or another type of irregular heart beat or heart rhythm problem, or if you have or have ever had low levels of magnesium or potassium, heart failure (HF; condition in which the heart cannot pump enough blood to other parts of the body), or liver disease.
• tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while receiving ondansetron, call your doctor.

What SPECIAL DIETARY instructions should I follow?

Unless your doctor tells you otherwise, continue your usual diet.

What SIDE EFFECTS can this medicine cause?

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

• headache
• constipation
• drowsiness
• feeling cold or chills; fever
• pain, burning, numbness, or tingling in the hand or feet
• injection site pain, redness, swelling, warmth, or burning

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

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

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

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What OTHER INFORMATION should I know?

Keep all appointments with your doctor.

Keep a written list of all of the prescription and nonprescription (over-the-counter) medicines, vitamins, minerals, and dietary supplements you are taking. Bring this list with you each time you visit a doctor or if you are admitted to the hospital. You should carry the list with you in case of emergencies.

^¶ This branded product is no longer on the market. Generic alternatives may be available.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS^® Patient Medication Information™ Copyright, 2026. The American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: September 15, 2026.