Ondansetron
A selective 5-HT3 receptor antagonist that prevents nausea and vomiting from chemotherapy, radiotherapy and surgery.
Drug card
- Class
- 5-HT3 antagonist
- How it works
- Blocking serotonin 5-HT3 receptors that trigger the vomiting reflex
- Used for
- Nausea and vomiting from chemotherapy or radiotherapy
- Nausea and vomiting after surgery
- Known for
- Headache
- Constipation
- QT prolongation and torsades de pointes
- Its name
- -setron means a 5-HT3 antagonist (antiemetic)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does ondansetron work?
A carbazole derivative that competitively blocks 5-HT3 receptors and, unlike metoclopramide, does not block dopamine receptors. CYP3A4, CYP2D6 and CYP1A2 all clear it, and it neither induces nor inhibits them; strong CYP3A4 inducers such as rifampicin, phenytoin and carbamazepine lower its levels.
Uses
What is ondansetron used for?
- Nausea and vomiting from chemotherapy or radiotherapy
- Nausea and vomiting after surgery
Side effects
Side effects of ondansetron
- HeadacheKnown for
- ConstipationKnown for
- QT prolongation and torsades de pointesKnown forSerious
- Diarrhea
- Tiredness and malaise
- Other arrhythmias, including slow heart rateSerious
- Myocardial ischemia from coronary artery spasmSerious
- Serotonin syndrome, mostly with other serotonergic drugsSerious
- Anaphylaxis and bronchospasmSerious
- Raised liver enzymes
- Dystonia and other extrapyramidal reactions (rare)
- Brief loss of vision, mainly with intravenous use
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated with apomorphine: together they have caused profound hypotension and loss of consciousness.
- Avoid in congenital long QT syndrome; monitor the ECG with electrolyte problems, heart failure or other QT-prolonging drugs.
- Watch for serotonin syndrome with SSRIs, SNRIs and other serotonergic drugs.
- It can hide a developing ileus after abdominal surgery and does not replace nasogastric suction.
Remember it
A way to remember it
Three for the 5-HT3s: headache, constipation and a longer QT.
Headache and constipation are the commonest side effects of ondansetron, and QT prolongation is the serious one to check for.
Written for biofideX
Its name
-setron means 5-HT3 antagonist (antiemetic)
Ondansetron blocks 5-HT3 receptors to prevent nausea and vomiting from chemotherapy, radiotherapy and surgery; granisetron and palonosetron share the stem.
- Every drug name stem
Its class
5-HT3 antagonists
5-HT3 antagonists block serotonin type 3 receptors on vagal nerve endings in the gut and in the chemoreceptor trigger zone. Chemotherapy and radiotherapy make enterochromaffin cells of the small intestine release serotonin, which excites vagal afferents through these receptors and sets off vomiting; blocking them breaks that loop. Whether the main site of action is central, peripheral or both is not settled.
Easily mixed up with dopamine antagonist antiemetics and triptans.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Stomach and gut
Ondansetron is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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