Antiemetic — 5-HT3 Antagonist

Ondansetron

Brand names: Zofran

Ondansetron is a 5-HT3 receptor antagonist antiemetic, used especially for nausea and vomiting related to chemotherapy, radiotherapy and surgery.

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 blocks 5-HT3 (serotonin) receptors centrally and in the gut, dampening the vomiting reflex.

Prescribing in practice

It prolongs the QT interval — use caution with other QT-prolonging drugs and in electrolyte disturbance, and avoid high single intravenous doses.
Constipation and headache are common.
Generally avoided in early pregnancy unless the benefit outweighs the risk (discuss).

Monitoring

Consider ECG and electrolytes where QT risk is high; review bowel habit.

Counselling the patient

It can cause constipation and headache.
Tell your clinician about other medicines, as some combinations affect heart rhythm.

Evidence & guidelines

A standard antiemetic for chemotherapy/radiotherapy and post-operative nausea and vomiting, with QT precautions.

Reference: MHRA Drug Safety Update 2013 (Ondansetron IV); 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways