BMA Concise Guide to Medicine & Drugs


Brand names Ondemet, Zofran

Used in the following combined preparations None


Drug group Anti-emetic drug

Overdose danger rating Low

Dependence rating Low

Prescription needed Yes

Available as generic Yes


Ondansetron, an anti-emetic, is used especially for treating the nausea and vomiting associated with radiotherapy and anticancer drugs. It may also be prescribed for the nausea and vomiting that occur after surgery.

The dose given and the frequency will depend on which anticancer drug you are having and its dose. In most instances, you will receive ondansetron, either by mouth or injection, before infusion of the anticancer agent, then tablets for up to five days after treatment has finished. The drug is less effective against the delayed nausea and vomiting that occur several days after chemotherapy than against symptoms that occur soon after treatment. For nausea and vomiting after surgery, one dose is usually given before the surgery, and two doses after.

To enhance the effectiveness of ondansetron, it is usually taken with other drugs, such as dexamethasone. Serious adverse effects are unlikely to occur.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets, liquid, injection, suppositories.

Frequency and timing of doses Normally 2 x daily but the frequency will depend on the reason for which the drug is being used.

Adult dosage range 4–32mg daily depending on the reason for which it is being used.

Onset of effect Within 1 hour.

Duration of action Approximately 12 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose Take as soon as you remember. If your next dose is due within 2 hours, take a single dose now and skip the next.

Stopping the drug Can be safely stopped as soon as you no longer need it.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice any unusual symptoms, or if a large overdose has been taken, notify your doctor.


Ondansetron is considered to be safe and is generally well tolerated. It does not cause the sedation or abnormal muscle movements that are adverse effects of some other anti-emetics. The most common adverse effects of ondansetron include constipation, headache, and a warm feeling in the head or stomach. Discuss with your doctor if these are severe. More rarely, palpitations, chest pain, muscle stiffness, or seizures may occur; if so, you should consult your doctor promptly. If you develop wheezing, an itchy rash, or swelling of the eyelids, lips, or face, you should stop taking the drug and contact your doctor immediately.


Carbamazepine, phenytoin and rifampicin These drugs may accelerate the breakdown of ondansetron and reduce its effect.

Apomorphine may cause a drop in blood pressure when used with ondansetron; the two drugs should not be taken together.

Vandetanib may increase the risk of heart rhythm abnormalities when used with ondansetron; the two drugs should not be taken together.

Tramadol The effect of this drug may be reduced by ondansetron.


Be sure to tell your doctor if:

· You have a long-term liver problem.

· You have bowel problems.

· You have heart rhythm problems.

· You are taking other medicines.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding The drug may pass into the breast milk. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 No special problems.

Driving and hazardous work No problems expected.

Alcohol No known problems.


Not generally prescribed for long-term treatment.