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Antiemetic

Ondansetron

Brand names: Zofran, Ondansetron 4mg

Ondansetron is a 5-HT3 receptor antagonist antiemetic used to prevent and treat post-operative nausea and vomiting and nausea and vomiting associated with chemotherapy and radiotherapy.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

See full prescribing information for the recommended dosage in adults and pediatrics (2) Patients with severe hepatic impairment: do not exceed a total daily dose of 8 mg ( 2.2 , 8.6 ) 2.1 Dosage The recommended dosage regimens for adult and pediatric patients are described in Table 1 and Table 2, respectively. Corresponding doses of ondansetron tablets may be used interchangeably. Table 1: Adult Recommended Dosage Regimen for Prevention of Nausea and Vomiting Indication Dosage Regimen Highly Emetogenic Cancer Chemotherapy A single 24 mg dose administered 30 minutes before the start of single-day highly emetogenic chemotherapy, including cisplatin greater than or equal to 50 mg/m 2 …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-04-24. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It selectively blocks 5-HT3 (serotonin) receptors peripherally on vagal afferents and centrally in the chemoreceptor trigger zone, interrupting the emetic reflex.

Prescribing in practice

  • It prolongs the QT interval, so observe dose limits and use with caution or avoid alongside other QT-prolonging drugs or uncorrected electrolyte disturbance.
  • Constipation and headache are common adverse effects.
  • In pregnancy (for example hyperemesis gravidarum) use only after weighing risks and benefits, as first-trimester use has been associated with a small increase in the risk of cleft palate.

Monitoring

Consider ECG and check electrolytes (including potassium and magnesium) in patients at risk of QT prolongation, and monitor bowel function.

Counselling the patient

  • This medicine can cause constipation and headache — let us know if these become troublesome.
  • Tell your doctor about any heart rhythm problems or other medicines you take, as some can affect your heartbeat.
  • Seek urgent help if you notice palpitations, fainting or an irregular heartbeat.

Evidence & guidelines

Widely guideline-recommended for chemotherapy-induced and post-operative nausea and vomiting; MHRA advice on QT prolongation and first-trimester use.

Reference: NICE; MHRA Ondansetron Safety Update 2013; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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