Pharmacology · 5-HT3 receptor antagonists (setrons)
Granisetron !
A 5-HT3 antagonist like ondansetron, used before chemotherapy, radiotherapy and surgery to prevent vomiting. Constipation and headache are common.
Updated 2026-11-01
Cryo-EM structure of the mouse 5-HT3A receptor with granisetron in the serotonin pocket between two subunits; the human receptor's pocket is closely similar.
Mechanism of action
Granisetron blocks the 5-HT3 receptor, a serotonin-gated ion channel, on vagal afferent nerves in the gut and in the brainstem (area postrema and nucleus of the solitary tract). Serotonin released from enterochromaffin cells after chemotherapy or radiation cannot open the channel, so the vomiting reflex is not triggered. It does not stimulate gut motility.
- Chemotherapy releases serotonin from gut enterochromaffin cells
- Granisetron occupies the serotonin pocket of 5-HT3 channels
- Vagal and brainstem signals for vomiting are blocked
- Nausea and vomiting are prevented
Pharmacokinetics
- Absorption
- Given by mouth or intravenously.
- Distribution
- About 65% bound to plasma proteins; it distributes freely into red blood cells.
- Metabolism
- Liver, by N-demethylation and ring oxidation, mainly through the CYP3A subfamily.
Indications
- Prevention of nausea and vomiting from emetogenic cancer chemotherapy, including high-dose cisplatin, and from radiotherapy.
- Prevention and treatment of post-operative nausea and vomiting in adults.
Adverse effects
Common
- Headache
- Constipation
- Fever and abdominal pain after surgery
- Raised liver enzymes
Contraindications
- Hypersensitivity to granisetron or any component
Key interactions
- QT-prolonging or arrhythmogenic drugs
- Additive QT prolongation.
- SSRIs, SNRIs, MAO inhibitors, mirtazapine, fentanyl, lithium, tramadol, IV methylene blue
- Serotonin syndrome.
- CYP inducers and inhibitors
- They can change granisetron clearance and half-life.
What is monitored
- ECG in patients with arrhythmias, conduction disease or QT-prolonging drugs
- Bowel function after abdominal surgery
- Signs of serotonin syndrome
Administration and safety
- Given before chemotherapy or radiotherapy, not on a regular schedule outside those times
- It does not stimulate the gut and does not replace nasogastric suction
- Routine prevention is not used in patients with little expected risk of post-operative vomiting
Nursing care
- Give the dose before chemotherapy or radiotherapy starts
- Ask about constipation and headache
- Review the medication list for QT-prolonging and serotonergic drugs
- Watch bowel sounds and distension after abdominal surgery
Pregnancy and breastfeeding
Animal studies at doses far above human ones showed no fetal harm; there are no adequate studies in pregnant women.
Test yourself
Think of the answer, then tap the question to see it.
Which receptor does granisetron block?
The serotonin 5-HT3 receptor, a ligand-gated ion channel.
Which two adverse effects of granisetron are most common?
Headache and constipation.
Why can granisetron be risky after abdominal surgery?
It does not stimulate motility and can mask a progressive ileus or gastric distension.
Related drugs
← Back to the class: 5-HT3 receptor antagonists (setrons)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - GRANISETRON HYDROCHLORIDE injection, solution (DailyMed (U.S. National Library of Medicine), 2026); Granisetron: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); RCSB PDB - 6NP0: Cryo-EM structure of 5HT3A receptor in presence of granisetron (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.