Ondansetron Viatris (Ondansetron)

Ondansetron acts on the serotonin 5‑HT3 pathway to reduce nausea and vomiting in several clinical settings.

• Chemotherapy‑induced nausea and vomiting: prevents and controls nausea and vomiting associated with cytotoxic cancer treatments.
• Postoperative nausea and vomiting: reduces the incidence of nausea and vomiting after surgical procedures.
• Radiotherapy‑induced nausea and vomiting: mitigates nausea and vomiting that occur during or after radiation therapy.

• Ondansetron selectively blocks serotonin 5‑HT3 receptors located in the chemoreceptor trigger zone of the brain and in vagal afferents of the gastrointestinal tract. By inhibiting these receptors, it interrupts the signaling cascade that triggers the vomiting reflex, thereby reducing both nausea and emesis.

Ondansetron is generally well tolerated, but adverse reactions can occur.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: reduced bowel movements.
• Dizziness: transient light‑headedness.
• Fatigue: feeling of tiredness.
• Diarrhoea: loose stools.
• Injection site pain: mild discomfort at the IV site.

Serious or Rare Side Effects

• QT interval prolongation: may lead to cardiac arrhythmias.
• Severe allergic reaction: rash, itching, swelling, or anaphylaxis.
• Serotonin syndrome: agitation, hyperthermia, muscle rigidity when combined with serotonergic agents.
• Cardiac arrhythmia: ventricular tachycardia or fibrillation.
• Hypotension: sudden drop in blood pressure.

Before using Ondansetron, clinicians should consider several safety measures.

• Cardiac assessment: evaluate baseline ECG and correct electrolyte imbalances.
• Concomitant QT‑prolonging drugs: avoid or monitor closely when used together.
• Hepatic impairment: use with caution in patients with liver dysfunction.
• Pregnancy and lactation: assess risk‑benefit as safety data are limited.
• Storage: Store at ambient temperature: keep in the original packaging, protect from moisture and light.

Ondansetron may interact with other medicines, requiring attention to avoid adverse outcomes.

Major Interactions (Avoid)

• Apomorphine: can cause severe hypotension and loss of consciousness.
• Other QT‑prolonging agents (e.g., quinidine, erythromycin): increase risk of cardiac arrhythmias.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin): may raise ondansetron plasma levels.
• CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce effectiveness.
• Opioid analgesics: may enhance serotonergic effects, raising serotonin syndrome risk.
• Anticholinergic drugs: may increase constipation incidence.