Ondansetron Orifarm (Ondansetron)

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

• Chemotherapy‑induced nausea and vomiting: reduces frequency and severity of acute and delayed episodes.
• Radiation‑induced nausea and vomiting: mitigates symptoms during and after radiotherapy.
• Post‑operative nausea and vomiting: prevents and treats nausea following 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 triggered by chemotherapeutic agents, radiation, or surgical stimuli, thereby reducing nausea and vomiting.

Ondansetron may cause a range of adverse reactions, from mild to serious.

Common Side Effects

• Headache: mild to moderate pain often transient.
• Constipation: reduced bowel movements, may require laxatives.
• Dizziness: sensation of light‑headedness, usually temporary.
• Fatigue: feeling of tiredness or lack of energy.
• Diarrhoea: loose stools, generally self‑limiting.
• Abdominal pain: mild discomfort in the stomach area.

Serious or Rare Side Effects

• QT prolongation: potential cardiac rhythm disturbance.
• Severe allergic reaction (anaphylaxis): rash, swelling, breathing difficulty.
• Serotonin syndrome: agitation, hyperreflexia, fever when combined with serotonergic drugs.
• Cardiac arrhythmia: irregular heartbeats, especially in predisposed patients.
• Severe hypotension: marked drop in blood pressure.
• Hepatic dysfunction: elevated liver enzymes or jaundice.

Before initiating therapy, clinicians should assess patient‑specific risk factors and monitor for adverse events.

• Cardiac assessment: evaluate history of arrhythmias or prolonged QT interval.
• Electrolyte monitoring: correct hypokalaemia or hypomagnesaemia to reduce QT risk.
• Hepatic function: use cautiously in patients with liver impairment.
• Concomitant QT‑prolonging drugs: avoid or monitor closely.
• Renal function: adjust dosing in severe renal impairment if required.
• Store at room temperature: keep in original packaging, protect from moisture and light.

Ondansetron can interact with several medication classes, necessitating careful review.

Major Interactions (Avoid)

• Apomorphine: may cause severe hypotension and loss of consciousness.
• Other 5‑HT3 antagonists: additive antiemetic effect can increase cardiac risk.
• QT‑prolonging agents (e.g., quinidine, amiodarone): heightened risk of arrhythmia.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may raise ondansetron plasma levels.
• CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce drug efficacy.
• Anticholinergic medications: can exacerbate constipation.