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5-HT3 Receptor Antagonist — Nausea / Vomiting / Gastroenteritis Pregnancy: Use with caution — limited data; hyperemesis gravidarum use is common (off-label) — appears safe but avoid in first trimester if possible

Ondansetron (Paediatric)

Brand names: Zofran, Ondansetron Orodispersible

Adult dose

Dose: 4–8 mg every 8–12 hours; chemotherapy: 8 mg then 8 mg every 8 hours
Route: Oral, IV, IM
Frequency: Every 8 hours
Max: 32 mg/day (chemotherapy — MHRA reduced to 32 mg/day)
Adult reference — see paediatric dose section

Paediatric dose

Dose: 0.15 mg/kg (max 4 mg per dose for <40 kg) mg/kg
Route: Oral (orodispersible or syrup), IV
Frequency: Every 8 hours (up to 3 doses/day)
Max: 4 mg per dose (<40 kg); 8 mg per dose (≥40 kg); max 12 mg/day in children
BNFc: licensed from 1 month for post-operative nausea/vomiting; for gastroenteritis (off-label but widely used in emergency settings) — single oral dose reduces vomiting and improves oral rehydration tolerance. MHRA 2013: IV single dose limit reduced to 4 mg for <40 kg children (QT concern). Orodispersible tablets (4 mg) particularly useful in vomiting children — dissolve on tongue.

Dose adjustments

Renal

No dose adjustment required

Hepatic

Severe hepatic impairment: max 8 mg/day — reduced hepatic clearance

Paediatric weight-based calculator

BNFc: licensed from 1 month for post-operative nausea/vomiting; for gastroenteritis (off-label but widely used in emergency settings) — single oral dose reduces vomiting and improves oral rehydration tolerance. MHRA 2013: IV single dose limit reduced to 4 mg for <40 kg children (QT concern). Orodispersible tablets (4 mg) particularly useful in vomiting children — dissolve on tongue.

Clinical pearls

  • Gastroenteritis evidence: PERN study and Cochrane review — single oral dose of ondansetron (0.15 mg/kg) in children with vomiting and gastroenteritis reduces vomiting episodes, improves rehydration success, and reduces IV fluid requirements; now standard practice in paediatric emergency departments
  • MHRA 2013 QT warning: IV dose limits for children — max 4 mg IV per dose for <40 kg; reduce further in hepatic impairment; avoid in QT prolongation risk
  • Do NOT use to suppress vomiting secondary to chemotherapy or radiation in children without antiemetic prophylaxis plan
  • Serotonin syndrome risk: caution with serotonergic medications — SSRIs, tramadol, linezolid; especially at high doses

Contraindications

  • Congenital long QT syndrome
  • Concurrent QT-prolonging drugs (relative)
  • Hypersensitivity to ondansetron

Side effects

  • Headache
  • Constipation
  • QTc prolongation (dose-dependent)
  • Flushing
  • Transient elevated LFTs
  • Dizziness

Interactions

  • QT-prolonging drugs (haloperidol, erythromycin, methadone) — additive QT prolongation
  • Apomorphine — severe hypotension
  • CYP3A4 inducers (phenytoin, carbamazepine) — reduce ondansetron levels

Monitoring

  • ECG (QTc — if IV use or risk factors)
  • Electrolytes (hypokalaemia worsens QT risk)
  • Clinical response (vomiting cessation, oral rehydration tolerance)

Reference: BNF for Children; MHRA Drug Safety Update 2013 (Ondansetron QT); PERN Study; Ramsook 2002 (Gastroenteritis RCT). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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