Ondansetron (Zofran): anti-sickness medicine for chemotherapy and after surgery

Ondansetron is an anti-emetic, a medicine that helps to stop you feeling or being sick. Zofran is the original brand name. Ondansetron is also available as generic tablets, orodispersible tablets that melt on the tongue, oral films and solution for injection or infusion, all of which are listed on the electronic medicines compendium.

The patient leaflet describes three licensed uses: preventing nausea and vomiting caused by chemotherapy in adults and children, preventing nausea and vomiting caused by radiotherapy for cancer in adults only, and preventing nausea and vomiting after surgery in adults only. It is used as prevention, which is why timing around treatment matters.

The NHS lists feeling sick and being sick among the common side effects of chemotherapy, and says your care team may be able to give you treatments to ease them. Anti-sickness medicine is one of those treatments, and your oncology team will normally decide on the exact combination.

According to the leaflet for 4 mg and 8 mg tablets, on the day of chemotherapy or radiotherapy the usual adult dose is 8 mg taken one to two hours before treatment and another 8 mg twelve hours afterwards. On the following days it is 8 mg twice a day, which may be given for up to 5 days. For children over 6 months the doctor decides the dose by body surface area or weight, with the usual dose for a child being up to 4 mg twice a day for up to 5 days.

To prevent sickness after an operation, the usual adult dose is 16 mg before the operation, and for children aged over 1 month it is recommended that it is given as an injection. People with moderate or severe liver problems should not have more than 8 mg in total per day.

Tablets should start to work within one or two hours. If you are sick within one hour of taking a dose, take the same dose again; otherwise do not take more than the label says. If you still feel sick, tell your doctor or nurse. Do not stop taking tablets without talking to a doctor, even if you feel well. If you forget a dose, take it when you remember unless the next one is nearly due, and never double up.

These figures come from one manufacturer leaflet, and your own instructions may differ. Follow the label on your pack and the advice of the oncology or surgical team.

The leaflet says you should not take ondansetron if you are allergic to it, if you have had an allergic reaction to similar anti-emetics such as granisetron or dolasetron, or if you are taking apomorphine, a Parkinson’s disease medicine.

It asks you to talk to your doctor first if you have a blockage in the gut or severe constipation, are due to have surgery on the adenoids or tonsils, have a heart problem such as heart failure, an uneven heartbeat, liver problems, or problems with potassium, sodium or magnesium levels in the blood.

The interaction list in the leaflet is long. It includes epilepsy medicines such as phenytoin and carbamazepine, rifampicin, tramadol, medicines that affect the heart such as haloperidol or methadone, anti-arrhythmics such as amiodarone, beta-blockers, some cancer medicines including anthracyclines and trastuzumab, antibiotics such as erythromycin, ketoconazole, SSRIs and SNRIs. Tell your doctor or pharmacist about everything you take, including herbal medicines.

On pregnancy, the leaflet says it should not be used in the first trimester because it can slightly increase the risk of a baby being born with cleft lip or cleft palate, and recommends effective contraception in sexually active women of childbearing potential. It says not to breastfeed while taking it. If you are already pregnant or planning a baby, ask your doctor or pharmacist for advice. For nausea in early pregnancy, the NHS has separate advice; it is a different situation from chemotherapy.

Headache is very common, affecting more than 1 in 10 people. Common effects, affecting up to 1 in 10, include a feeling of warmth or flushing, constipation, and changes in liver function test results, particularly when taken with cisplatin. Uncommon effects include hiccups, low blood pressure that can make you faint or dizzy, an uneven heartbeat, chest pain, fits and unusual body movements.

Rare effects include dizziness, blurred vision and disturbance in heart rhythm, sometimes causing sudden loss of consciousness. Very rare effects include poor vision or temporary loss of eyesight, which usually comes back within 20 minutes.

The leaflet says to stop the medicine and seek medical help immediately for allergic reactions, including sudden wheezing and chest pain or tightness, swelling of the eyelids, face, lips, mouth or tongue, hives or collapse, and for signs of reduced blood flow to the heart such as sudden chest pain or tightness. The NHS advises calling 999 or going to A&E for serious allergic reactions.

If you take too many tablets, contact your doctor as soon as possible or go to the nearest emergency department and take the packet. The leaflet says an overdose may cause problems with vision, low blood pressure or an irregular heartbeat.

The NHS chemotherapy page says that feeling sick and being sick are common side effects, and that your care team can often help with treatments and advice. It advises calling your care team straight away if you have a high temperature, signs of infection, or a throbbing painful swollen leg or arm, sudden breathlessness or chest pain. If you cannot reach them, call NHS 111.

The NHS page on feeling sick gives general self-care tips: fresh air, small sips of cold drinks, ginger or peppermint tea, smaller more frequent meals, avoiding strong smells and greasy food. It advises seeing a GP if you often feel sick or do not feel better in a few days, and says the GP may prescribe anti-sickness medicine if needed. If you are being sick you can become dehydrated.

If your sickness keeps breaking through despite ondansetron, tell your care team. The NHS says they may be able to give you treatments to ease side effects and advice about things you can do.

Ondansetron is prescribed by oncology teams, surgeons, anaesthetists and GPs, in NHS and private settings alike. The decisions are the same: which combination of anti-sickness medicines to use around a treatment, and for how long. Always ask your team for a written plan that says what to take and when, and who to call if it is not working.