Ondansetron Viatris (Ondansetron)

Ondansetron is a selective 5‑HT3 receptor antagonist used to control nausea and vomiting in several clinical settings.

• Chemotherapy‑induced nausea and vomiting: reduces the incidence and severity of acute and delayed nausea and vomiting.
• Radiation‑induced nausea and vomiting: provides prophylaxis for patients receiving radiotherapy.
• Postoperative nausea and vomiting: helps prevent nausea and vomiting after surgical procedures.

• Ondansetron blocks serotonin (5‑HT3) receptors located centrally in the chemoreceptor trigger zone and peripherally on vagal nerve terminals. By inhibiting these receptors, it prevents the initiation of the vomiting reflex that is triggered by chemotherapeutic agents, radiation, or surgical stimuli, thereby reducing nausea and vomiting.

Common side effects are generally mild and transient.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: reduced bowel movements.
• Dizziness: sensation of light‑headedness.
• Fatigue: feeling unusually tired.
• Diarrhoea: loose stools.
• Abdominal pain: mild discomfort.

Serious or Rare Side Effects

• QT interval prolongation: may lead to cardiac arrhythmias.
• Severe allergic reactions: including anaphylaxis and skin rash.
• Serotonin syndrome: when combined with other serotonergic drugs.
• Cardiac arrhythmias: irregular heart rhythms.
• Stevens‑Johnson syndrome: severe skin and mucous membrane reaction.
• Hepatic dysfunction: abnormal liver enzyme elevations.

Before initiating therapy, consider patient‑specific risk factors and monitoring requirements.

• Cardiac risk assessment: evaluate history of QT prolongation or electrolyte disturbances.
• Hepatic impairment: use with caution and consider dose adjustment.
• Renal impairment: monitor renal function and adjust dose if needed.
• Hypersensitivity: avoid in patients with known allergy to ondansetron or similar compounds.
• Drug‑specific monitoring: observe for signs of serotonin syndrome when combined with serotonergic agents.
• Store at room temperature: keep in the original packaging, protect from moisture and direct sunlight.

Ondansetron may interact with several medication classes; some require avoidance while others need close monitoring.

Major Interactions (Avoid)

• Apomorphine: concurrent use can cause severe hypotension and loss of consciousness.
• Certain anti‑arrhythmic agents (e.g., amiodarone): increase risk of QT prolongation.
• Serotonergic agents (e.g., SSRIs, MAO inhibitors): may precipitate serotonin syndrome.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may raise ondansetron plasma levels.
• CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce ondansetron effectiveness.