5-HT3 Receptor Antagonist (Antiemetic) Pregnancy: Caution — observational data suggests possible orofacial cleft risk in first trimester; use in 2nd/3rd trimester generally accepted

Ondansetron (Perioperative)

Brand names: Zofran

Adult dose

Dose: PONV prevention: 4 mg IV at induction or end of surgery. Treatment of PONV: 4 mg IV. Chemotherapy-induced NVOM: 8 mg IV/oral BD–TDS.

Route: IV slow bolus or oral

Frequency: Single dose (perioperative); BD–TDS (chemotherapy)

Max: 32 mg/day (8 mg per IV dose — QTc risk with higher doses)

QTc prolongation risk — MHRA 2013: max 32 mg single IV dose removed; max single IV dose 16 mg. Previous 32 mg single IV dose no longer recommended. Dexamethasone 4 mg IV combination more effective for PONV.

Paediatric dose

Dose: 0.1 mg/kg

Route: IV

Frequency: Single dose perioperatively; max TDS for CINV

Max: 4 mg per dose (max 8 mg/day)

Concentration: 2 mg/mL mg/ml

Children ≥6 months: 0.1 mg/kg IV (max 4 mg). CINV: 3 doses of 0.15 mg/kg every 4h. Do NOT administer to infants <1 month.

Dose adjustments

Renal

No dose adjustment required

Hepatic

Maximum 8 mg/day in severe hepatic impairment (reduced clearance)

Paediatric weight-based calculator

Patient weight (kg)

Children ≥6 months: 0.1 mg/kg IV (max 4 mg). CINV: 3 doses of 0.15 mg/kg every 4h. Do NOT administer to infants <1 month.

Clinical pearls

MHRA 2013: 32 mg single IV dose abolished due to QT prolongation — maximum 16 mg single IV dose
Multimodal PONV prevention: dexamethasone 4 mg + ondansetron 4 mg most evidence-based combination
Aprepitant (NK1 antagonist) + ondansetron + dexamethasone: triple therapy for high-risk PONV
Constipation common — not the antiemetic of choice in patients with bowel obstruction/ileus

Contraindications

Congenital long QT syndrome
Hypomagnesaemia/hypokalaemia (correct before use)
Concomitant QT-prolonging drugs (caution)

Side effects

Headache
Constipation
QT prolongation (dose-dependent)
Dizziness
Flushing
Transient LFT elevation

Interactions

QT-prolonging drugs — additive QT prolongation
Apomorphine — severe hypotension (contraindicated)
Tramadol — serotonin syndrome risk

Monitoring

ECG (QTc) if at risk
Electrolytes (K+, Mg2+) before high-dose use
PONV response

Reference: BNFc; BNF; MHRA Drug Safety Update 2013; Apfel PONV Risk Score. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways