Ondansetron Teva Pharma B.V. (Ondansetron)

Ondansetron is a selective 5‑HT3 receptor antagonist used across several emetic pathways.

• Chemotherapy‑induced nausea and vomiting: helps control acute and delayed episodes in cancer patients.
• Radiotherapy‑induced nausea and vomiting: reduces the frequency and severity of nausea during radiation treatment.
• Post‑operative nausea and vomiting: prevents nausea and vomiting after surgical procedures.
• Pregnancy‑related nausea (hyperemesis gravidarum): used when other treatments are ineffective, under specialist supervision.

• Ondansetron blocks the serotonin 5‑HT3 receptors located on vagal afferent nerves in the gastrointestinal tract and in the chemoreceptor trigger zone of the brain. By inhibiting this receptor, it prevents serotonin‑mediated stimulation of the vomiting centre, thereby reducing the incidence of nausea and vomiting.

Adverse reactions to ondansetron are generally mild to moderate, but serious events can occur.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: occasional bowel movement difficulty.
• Diarrhoea: loose stools, usually transient.
• Fatigue: feeling of tiredness or reduced energy.
• Dizziness: light‑headed sensation.
• Injection site pain (if administered intravenously).

Serious or Rare Side Effects

• Cardiac arrhythmia: QT‑interval prolongation, especially with rapid IV administration.
• Severe allergic reaction: rash, itching, swelling, or anaphylaxis.
• Serotonin syndrome: rare when combined with other serotonergic agents.
• Hepatic dysfunction: elevated liver enzymes.
• Severe constipation or intestinal obstruction.
• Vision changes: blurred vision or visual disturbances.

When prescribing ondansetron, clinicians should consider several safety aspects.

• Cardiac monitoring: assess baseline ECG in patients with known cardiac disease.
• Electrolyte balance: correct hypokalaemia or hypomagnesemia before use.
• Concomitant serotonergic drugs: evaluate risk of serotonin syndrome.
• Pregnancy: use only if benefit outweighs risk; discuss with obstetric specialist.
• Pediatric dosing: ensure weight‑based dosing calculated by prescriber.
• Store at below 25°C: keep in the original container, protect from moisture and direct sunlight.

Ondansetron may interact with several drug classes, requiring vigilance.

Major Interactions (Avoid)

• Apomorphine: may cause profound hypotension and loss of consciousness.
• Certain anti‑arrhythmic agents (e.g., quinidine, amiodarone): increase risk of QT prolongation.
• Tramadol and other serotonergic analgesics: heightened risk of serotonin syndrome.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin): may raise ondansetron plasma levels.
• CYP2D6 substrates (e.g., codeine, metoprolol): potential altered metabolism.
• Anticholinergic agents: may enhance anticholinergic side‑effects.
• Diuretics: monitor electrolytes, especially potassium and magnesium.
• Oral contraceptives: may slightly reduce efficacy, advise alternative contraception if needed.