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# 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

- Class: [5-HT3 receptor antagonists (setrons)](https://durgical.com/en/pharmacology/classes/5-ht3-receptor-antagonists/)
- Ion channel: Serotonin 5-HT3A receptor
- ATC code: A04AA02

⇅**Serotonin 5-HT3A receptor**Granisetron

ⓘ 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.

**Target in 3D:** Serotonin 5-HT3A receptor. PDB structure 6NP0 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6NP0) · Drag to rotate · pinch to zoom

## 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

### Serious (rare, important)

- QT prolongation
- Serotonin syndrome, mostly with other serotonergic drugs
- Masking of a progressive ileus or gastric distension
- Hypersensitivity reactions

## 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.

## Memory aid

«GRANIsetron, the GRANDchild of ondansetron»: same 5-HT3 block, same constipation and QT caution.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/granisetron/)

## Related drugs

- [Ondansetron](https://durgical.com/en/pharmacology/ondansetron/)
- [Palonosetron](https://durgical.com/en/pharmacology/palonosetron/)

[← Back to the class: 5-HT3 receptor antagonists (setrons)](https://durgical.com/en/pharmacology/classes/5-ht3-receptor-antagonists/)

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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8d88adba-7f5e-4e97-84b3-6ca8ec98c023) (DailyMed (U.S. National Library of Medicine), 2026); [Granisetron: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a601211.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [RCSB PDB - 6NP0: Cryo-EM structure of 5HT3A receptor in presence of granisetron](https://www.rcsb.org/structure/6NP0) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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