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5-HT3 Receptor Antagonist — Antiemetic Pregnancy: Use with caution — limited data in first trimester; commonly used for hyperemesis gravidarum under specialist guidance (UK national guidance supports use); no proven teratogenicity

Ondansetron (Burns/Procedural Antiemetic)

Brand names: Zofran

Adult dose

Dose: 4–8 mg IV or oral; post-operative nausea: 4 mg IV at end of procedure; CINV: 8 mg IV before chemotherapy; procedural sedation nausea: 4 mg IV
Route: IV (slow over 2–5 min) / IM / Oral / Orodispersible tablet
Frequency: Every 4–6 hours as needed; max 3 doses per day IV
Max: 32 mg/day (oral); 24 mg/day (IV) — MHRA 2012 reduced IV dose cap
First-line antiemetic in burns units for post-procedure nausea, opioid-induced nausea, and perioperative use. Particularly useful in burns patients who require frequent dressing changes under sedation (ketamine + ondansetron combination reduces ketamine-induced emesis). No sedative effect — does not compromise respiratory monitoring.

Paediatric dose

Dose: 0.1 mg/kg
Route: IV (over 15 min)
Frequency: Every 4–6 hours
Max: 4 mg per dose (under 2 years); 8 mg per dose (2–18 years)
Paediatric PONV: 0.1 mg/kg IV (max 4 mg). Children 1 month–2 years: 0.1 mg/kg IV. Children ≥2 years: same 0.1 mg/kg (max 4 mg single dose, max 3 doses/day). Do NOT give to neonates — limited data.

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Severe hepatic impairment: maximum 8 mg/day IV — impaired metabolism causes accumulation.

Paediatric weight-based calculator

Paediatric PONV: 0.1 mg/kg IV (max 4 mg). Children 1 month–2 years: 0.1 mg/kg IV. Children ≥2 years: same 0.1 mg/kg (max 4 mg single dose, max 3 doses/day). Do NOT give to neonates — limited data.

Clinical pearls

  • MHRA 2012 dose restriction: IV ondansetron capped at 32 mg single dose (was previously 32 mg) and routine 32 mg IV dose withdrawn due to QTc prolongation deaths — current safe IV dose is 4 mg or 8 mg; always verify local protocol
  • Ketamine + ondansetron combination: ketamine is the primary burns dressing-change sedation agent; co-administration of ondansetron 4 mg IV significantly reduces ketamine-induced nausea/vomiting (30% rate with ketamine alone) — standard at most UK burns units
  • Serotonin syndrome — rare but real: ondansetron is a 5-HT3 antagonist; when combined with tramadol (5-HT reuptake inhibitor), serotonin syndrome has been reported — agitation, clonus, hyperthermia. Monitor if combination used

Contraindications

  • Congenital long QT syndrome
  • Concurrent QT-prolonging drugs where risk exceeds benefit

Side effects

  • QT prolongation (dose-dependent — MHRA 2012 restricted single IV dose to 32 mg max due to Torsades risk; now 4–8 mg per dose)
  • Headache
  • Constipation
  • Transient LFT elevation
  • Serotonin syndrome (rare — at very high doses or with other serotonergic drugs)

Interactions

  • QT-prolonging drugs (antipsychotics, amiodarone, methadone — additive QTc risk; MHRA warning)
  • Apomorphine (absolute contraindication — profound hypotension)
  • Serotonergic drugs (SSRIs, tramadol — rare serotonin syndrome risk)

Monitoring

  • ECG (QTc before and after IV ondansetron if QT risk factors or high-dose)
  • Electrolytes (hypokalaemia and hypomagnesaemia worsen QT risk)
  • Nausea/vomiting control
  • LFTs (hepatic impairment monitoring)

Reference: BNFc; BNF 90; MHRA Drug Safety Update 2012 (QT prolongation); BNFc; British Burns Association Analgesia Guidelines; NICE CG174. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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