Ondansetron

💊 What is Ondansetron used for?

• •The label says ondansetron is used to prevent nausea and vomiting caused by: highly emetogenic cancer chemotherapy (chemotherapy strongly linked to vomiting, including cisplatin at or above a certain strength); initial and repeat courses of moderately emetogenic cancer chemotherapy; radiotherapy to certain body areas (total body, or the abdomen); and after surgery (postoperative nausea and/or vomiting).

How it works

The label describes ondansetron as a selective blocking agent of the serotonin 5-HT3 receptor type. It does not say more about how this works in the body.

How it is usually taken

• •The label says ondansetron tablets and orally disintegrating tablets may be used in place of each other at matching doses. The label says the timing of each dose is set around the start of chemotherapy, radiotherapy, or surgery, so the schedule can vary. Follow the instructions from your prescriber or pharmacist. For orally disintegrating tablets, the label says not to remove the tablet from the blister until just before use, and not to push it through the foil. With dry hands, peel back the foil, gently remove the tablet, and place it on top of the tongue, where it dissolves in seconds. Then swallow with saliva. The label says liquid is not needed.

Comes as

• •Ondansetron tablets, 4 mg (white, oval, film-coated, marked with a 4 and G1 logo)
• •Ondansetron tablets, 8 mg (yellow, oval, film-coated, marked with an 8 and G1 logo)
• •Ondansetron orally disintegrating tablets, 4 mg (white, round, uncoated, marked G and 4)
• •Ondansetron orally disintegrating tablets, 8 mg (white, round, uncoated, marked G and 8)

⚠️ Ondansetron side effects

🛑 Who should not take Ondansetron, and who should be careful

The label says not to take it if

• 🚨You have had a known allergic reaction (hypersensitivity, including anaphylaxis) to ondansetron or any ingredient in the product.
• 🚨You are receiving apomorphine. The label says the combination may cause a significant drop in blood pressure and loss of consciousness.

Tell your doctor before taking it if

• •Tell your prescriber about any past allergic reaction to ondansetron or its ingredients, because the label lists this as a reason not to take it.
• •Tell your prescriber if you have a heart rhythm problem, such as congenital long QT syndrome, low potassium or magnesium, heart failure, or slow heart rhythms. The label says these conditions need extra caution and heart monitoring.
• •Tell your prescriber about all medicines you take, especially apomorphine, medicines for depression or migraine, and tramadol.
• •Tell your prescriber if you have liver problems. The label discusses dosing limits for severe liver impairment.
• •If you have phenylketonuria, tell your prescriber. The label says orally disintegrating tablets contain phenylalanine, a component of aspartame.

🔀 Ondansetron with other medicines, food and alcohol

The label says to discuss these with your doctor or pharmacist

• •Apomorphine: The label says this combination is not allowed, because it may cause a severe drop in blood pressure and loss of consciousness.
• •Other serotonin-affecting medicines, such as SSRIs, SNRIs, MAO inhibitors, mirtazapine, fentanyl, lithium, tramadol, and methylene blue: The label says serotonin syndrome has been reported with these combinations, and some cases were fatal.
• •Tramadol: The label says ondansetron may increase how much tramadol patients give themselves through controlled dosing, so pain control should be monitored.
• •Phenytoin, carbamazepine, and rifampin: The label says these can speed up how the body clears ondansetron. The label says no dose change is recommended for these medicines.
• •Alfentanil and atracurium: The label says ondansetron does not change their respiratory depressant or neuromuscular blocking effects.
• •Carmustine, etoposide, and cisplatin: The label says these do not change how ondansetron is processed by the body.

Alcohol and food

The label does not say.

🤰 Ondansetron in pregnancy and breastfeeding

Pregnancy

The label says published studies on ondansetron and major birth defects have given inconsistent results, with important limitations, so the studies cannot confirm safety in pregnancy. The label says postmarketing data have not identified a drug-associated risk of miscarriage or adverse maternal outcomes. In animal studies, rats and rabbits did not show evidence of harm to the fetus at multiples of the maximum recommended human dose. The label notes that all pregnancies carry a background risk of birth defects and miscarriage. Talk with your prescriber about pregnancy questions.

Breastfeeding

The label does not say.

🗓️ Storage, missed doses and taking too much

Storage

The label does not say.

If a dose is missed

The label does not say.

If too much is taken

The label says there is no specific antidote for ondansetron overdose, so patients are managed with supportive care. The label describes reported effects in overdose cases, including temporary sudden blindness with severe constipation, low blood pressure with faintness, a fainting episode with a temporary heart block, and serotonin syndrome in some pediatric cases. If you think someone has taken too much, seek emergency medical help right away.

🗒️ Questions to ask about Ondansetron

• Which of my medicines could interact with ondansetron, including apomorphine, tramadol, or medicines for depression or migraines?
• Do I have any heart rhythm or electrolyte conditions that the label says need extra monitoring?
• Which form, tablet or orally disintegrating tablet, is right for my situation, and how should I use it?
• What signs of serotonin syndrome or allergic reaction should I watch for, and who should I call?
• If I have surgery or radiation, how will the timing of ondansetron be set for me?
• What should I do if I think I took too much or missed a dose?

❓ Ondansetron: frequently asked questions