Section 11 · Monograph
Ondansetron
Reviewed Nov 2026FDA label
Zofran5-HT3 antagonist
- Forms
- Tab: 4, 8mg | ODT: 4, 8mg | IV: 2mg/mL
- Dose
- 4-8mg q8h PRN
- MOA
- Blocks 5-HT3 receptors (antiemetic)
Indications
- Prevention of nausea and vomiting associated with chemotherapy, radiotherapy and postoperative statesFDA-labeled
Off-Label Uses
- Nausea associated with acute vestibular disorders or migraineOff-label
Mechanism of Action
- Selective 5-HT3 receptor antagonist acting on peripheral vagal afferents and the central chemoreceptor trigger zone
Full Dosing
Adult / usual
- 4-8mg orally, as ODT or IV every 8 hours as needed
- Maximum single IV dose 16mg (QT prolongation risk)
Hepatic
- Severe hepatic impairment (Child-Pugh C): maximum 8mg/day
Contraindications
- Concomitant use with apomorphine (profound hypotension)
- Known hypersensitivity to ondansetron or other selective 5-HT3 antagonists
Drug Interactions
- Serotonergic drugs: serotonin syndrome
- Other QT-prolonging drugs
- Apomorphine contraindicated
- CYP3A4 inducers (phenytoin, carbamazepine, rifampin) reduce levels
Adverse Effects
- Headache, constipation, fatigue
- QT prolongation and torsades de pointes
- Serotonin syndrome
- Hypersensitivity reactions
Monitoring Parameters
- ECG in patients with electrolyte abnormalities, long QT syndrome or heart failure
- Electrolytes
Pregnancy & Lactation
- Limited data; some studies suggest a possible small increase in oral clefts with first-trimester use
- Unknown whether present in human milk