Antiemetic — 5-HT3 Antagonist
Pregnancy: Caution — avoid in 1st trimester; observational data suggests association with cleft palate; use in 2nd/3rd trimester only if essential
Ondansetron
Brand names: Zofran
Adult dose
Dose: 4–8 mg
Route: Oral / IM / IV
Frequency: Every 8–12 hours
Max: 32 mg/day oral; 8 mg IV single dose (MHRA restriction)
PONV/chemotherapy-induced nausea: 8 mg oral or 4–8 mg IV/IM. MHRA 2013: max single IV dose reduced to 8 mg (risk of QT prolongation). Inject IV slowly over at least 15 minutes.
Paediatric dose
Dose: 0.1 mg/kg
Route: Oral / IV
Frequency: Every 4–12 hours
Max: 4 mg/dose
Chemotherapy-induced vomiting: 0.1 mg/kg (max 4 mg) IV over 15 minutes. Oral: 4 mg 3 times daily for children ≥4 years.
Dose adjustments
Renal
No dose adjustment required.
Hepatic
Severe hepatic impairment: max 8 mg/day.
Paediatric weight-based calculator
Chemotherapy-induced vomiting: 0.1 mg/kg (max 4 mg) IV over 15 minutes. Oral: 4 mg 3 times daily for children ≥4 years.
Clinical pearls
- MHRA 2013: IV bolus dose reduced to max 8 mg due to dose-dependent QT prolongation
- First-line for chemotherapy-induced and post-operative nausea and vomiting
- No significant dopaminergic blockade — safe in Parkinson's disease (unlike metoclopramide/domperidone)
Contraindications
- Congenital long QT syndrome
- Concurrent QT-prolonging drugs
Side effects
- Headache
- Constipation
- QT prolongation (especially IV)
- Flushing
- Dizziness
- Serotonin syndrome (rare — with concurrent serotonergic drugs)
Interactions
- QT-prolonging drugs (additive risk — avoid)
- Serotonergic drugs (SSRIs, tramadol — serotonin syndrome risk)
- Apomorphine (severe hypotension — contraindicated)
Monitoring
- ECG if risk factors for QT prolongation
- Electrolytes (hypokalaemia/hypomagnesaemia increase QT risk)
Reference: BNFc; BNF 90; MHRA Drug Safety Update 2013 (Ondansetron IV); BNFc. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators