Ondansetron Mercury Pharmaceuticals Limited (Ondansetron)

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

• Chemotherapy-induced nausea and vomiting: helps prevent and treat nausea and vomiting caused by cancer chemotherapy.
• Radiotherapy-induced nausea and vomiting: reduces nausea and vomiting associated with radiation treatment.
• Postoperative nausea and vomiting: prevents and treats nausea and vomiting after surgery.

• Ondansetron selectively blocks serotonin (5‑HT3) receptors located on vagal afferent nerves and in the chemoreceptor trigger zone of the brain. By antagonizing these receptors, it inhibits activation of the vomiting centre that is triggered by chemotherapy, radiotherapy, or surgical stimuli, thereby reducing the sensation of nausea and the reflex of vomiting.

Ondansetron may cause a range of adverse reactions, which are classified by frequency and severity.

Common Side Effects

• Headache: mild to moderate headache.
• Constipation: reduced bowel movements.
• Diarrhoea: loose stools.
• Fatigue: feeling of tiredness.

Serious or Rare Side Effects

• Cardiac arrhythmia: QT interval prolongation leading to irregular heartbeat.
• Severe allergic reaction: rash, itching, swelling, or difficulty breathing.
• Serotonin syndrome: rare but potentially life‑threatening condition when combined with other serotonergic agents.
• Hepatic dysfunction: elevated liver enzymes indicating liver stress.

When prescribing ondansetron, clinicians should consider several precautionary measures to ensure safe use.

• Cardiac monitoring: assess baseline ECG in patients with known heart disease or electrolyte abnormalities.
• Drug interactions: review concomitant medications that may affect QT interval or serotonin levels.
• Pregnancy: evaluate risk‑benefit as safety data are limited.
• Renal impairment: adjust dose or monitor in patients with severe kidney dysfunction.
• Hepatic impairment: use caution in patients with liver disease.
• Store at ambient temperature: keep below 25 °C, retain in original packaging, protect from moisture and light.

Ondansetron can interact with other medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Antipsychotics (e.g., haloperidol, droperidol): may increase risk of QT prolongation.
• Certain antiarrhythmics (e.g., amiodarone, quinidine): can potentiate cardiac rhythm disturbances.
• High‑dose serotonergic agents (e.g., SSRIs, MAO inhibitors): risk of serotonin syndrome.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may raise ondansetron plasma levels.
• CYP2D6 substrates (e.g., codeine, tramadol): ondansetron may reduce their analgesic effect.
• Oral contraceptives: possible reduced effectiveness; monitor for contraceptive failure.