Health Centres - Ondemet (ondansetron)
How does it work?
Ondemet tablets and injection contain the active ingredient ondansetron hydrochloride dihydrate, which is a type of medicine called a 5HT
Vomiting is controlled by an area of the brain called the vomiting centre. The vomiting centre is responsible for causing feelings of sickness (nausea) and for the vomiting reflex. It is activated when it receives nerve messages from another area of the brain called the chemoreceptor trigger zone (CTZ) and when it receives nerve messages from the gut.
Chemotherapy, radiotherapy and surgery can cause a substance called serotonin (5HT) to be released in the gut. This 5HT acts on the 5HT
5HT released by chemotherapy, radiotherapy and surgery also activates the 5HT
Ondansetron works by blocking the 5HT
Ondansetron can be given by mouth, by injection into a muscle or vein, by drip into a vein (intravenous infusion), or by suppository (see the Zofran suppositories factsheet linked at the end of this factsheet).
What is it used for?
- Preventing and treating nausea and vomiting caused by chemotherapy or radiotherapy for cancer
- Preventing and treating nausea and vomiting following surgery.
Use with caution in
- Allergy to other 5HT
- Decreased liver function
- Blockage of the gut (intestinal obstruction)
- Disurbances of the levels of salts (electrolytes) such as potassium, sodium and magnesium in the blood
- History of heart problems
- Irregular heart beats (arrhythmias)
- People taking medicines to treat an irregular heart beat (antiarrhythmics) or beta-blocker medicines.
Not to be used in
- Known hypersensitivity or allergy to any ingredient.
- Ondemet tablets contain lactose and should not be taken by people with rare hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption.
Pregnancy and Breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
- The safety of this medicine during pregnancy has not been established. It is not recommended for use in pregnant women unless considered essential by your doctor. Seek medical advice from your doctor.
- This medicine may pass into breast milk. Mothers who need to take this medicine should not breastfeed their infants during treatment. Seek medical advice from your doctor.
Side effects
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.
- Headache
- Constipation
- Flushing
- Hiccups
- Allergy to active ingredient (hypersensitivity)
- Involuntary movements
- Alteration in results of liver function tests
- Low blood pressure (hypotension)
- Chest pain
- Slow heart rate (bradycardia)
- Abnormal heart beats (arrhythmias)
- Seizures
The side effects listed above may not include all of the side effects reported by the drug's manufacturer.
How can this medicine affect other medicines?
It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.
The following medicines may increase the removal of ondansetron from the body and could therefore make it less effective:
- carbamazepine
- phenytoin
- rifampicin.
Small studies suggest that ondansetron may reduce the painkilling effect of tramadol.
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