Ondansetron

What it is and how it works

Mechanism of Action Ondansetron is a selective 5-HT 3 receptor antagonist. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. Serotonin receptors of the 5-HT 3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron’s antiemetic action is mediated centrally, peripherally, or in both sites. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine.

Indications

Ondansetron oral solution is indicated for the prevention of nausea and vomiting associated with: highly emetogenic cancer chemotherapy, including cisplatin greater than or equal to 50 mg/m 2 initial and repeat courses of moderately emetogenic cancer chemotherapy radiotherapy in patients receiving either total body irradiation, single high-dose fraction to the abdomen, or daily fractions to the abdomen Ondansetron oral solution is also indicated for the prevention of postoperative nausea and/or vomiting. Ondansetron oral solution is a 5-HT 3 receptor antagonist indicated for the prevention of: nausea and vomiting associated with highly emetogenic cancer chemotherapy, including cisplatin greater than or equal to 50 mg/m 2 . nausea and vomiting associated with initial and repeat courses of moderately emetogenic cancer chemotherapy. nausea and vomiting associated with radiotherapy in patients receiving either total body irradiation, single high-dose fraction to the abdomen, or daily fractions to the abdomen. postoperative nausea and/or vomiting.

Dosage and administration (summary)

See full prescribing information for the recommended dosage in adults and pediatrics. Patients with severe hepatic impairment: do not exceed a total daily dose of 8 mg. (2.2, 8.6) Dosage The recommended dosage regimens for adult and pediatric patients are described in Table 1 and Table 2, respectively. 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 .

Contraindications

Ondansetron is contraindicated in patients: known to have hypersensitivity (e.g., anaphylaxis) to ondansetron or any of the components of the formulation receiving concomitant apomorphine due to the risk of profound hypotension and loss of consciousness Patients known to have hypersensitivity (e.g., anaphylaxis) to ondansetron or any components of the formulation. Concomitant use of apomorphine.

Warnings and precautions

Hypersensitivity Reactions, Including Anaphylaxis and Bronchospasm: Discontinue ondansetron if suspected. Monitor and treat promptly per standard of care until signs and symptoms resolve. QT Interval Prolongation and Torsade de Pointes : Avoid ondansetron in patients with congenital long QT syndrome; monitor with electrocardiograms (ECGs) if concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or use of other QT prolonging drugs. Serotonin Syndrome: Reported with 5-HT 3 receptor antagonists alone but particularly with concomitant use of serotonergic drugs.

Pregnancy

Pregnancy Risk Summary Published epidemiological studies on the association between ondansetron use and major birth defects have reported inconsistent findings and have important methodological limitations that preclude conclusions about the safety of ondansetron use in pregnancy (see Data) .

Storage and supply

Ondansetron oral solution, USP a clear, colorless to light yellow liquid with a characteristic strawberry odor, contains 5 mg of ondansetron hydrochloride dihydrate equivalent to 4 mg of ondansetron per 5 mL. It is available as follows: 40 x 5mL unit dose cups in a tray NDC 50268-647-14 Store at 20º to 25ºC (68º to 77ºF).

Source: Ondansetron (Ondansetron) — US FDA prescribing information, 2026-01-09, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.