Ondansetron Accord Healthcare Ireland (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 frequency and severity of nausea and vomiting caused by cytotoxic chemotherapy.
• Radiation‑induced nausea and vomiting: prevents nausea and vomiting associated with radiation treatment.
• Postoperative nausea and vomiting: helps prevent nausea and vomiting after surgical procedures.

• Ondansetron blocks serotonin (5‑HT3) receptors located on vagal afferents in the gastrointestinal tract and in the chemoreceptor trigger zone of the brainstem. By inhibiting these receptors, it prevents serotonin‑mediated activation of the vomiting centre, thereby reducing the stimulus for nausea and emesis triggered by chemotherapy, radiation, or surgical stress. The antagonism is rapid and reversible, providing effective control of acute emetic episodes without affecting dopamine pathways.

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

Common Side Effects

• Headache: mild to moderate pain in the head.
• Constipation: reduced bowel movements.
• Diarrhoea: loose stools.
• Dizziness: sensation of light‑headedness.
• Fatigue: feeling of tiredness.
• Abdominal pain: discomfort in the stomach area.

Serious or Rare Side Effects

• QT interval prolongation: cardiac rhythm disturbance that can lead to arrhythmia.
• Severe allergic reaction: rash, swelling, or anaphylaxis.
• Serotonin syndrome: agitation, hyperreflexia, and autonomic instability when combined with other serotonergic agents.
• Cardiac arrhythmias: irregular heartbeats beyond QT prolongation.
• Stevens‑Johnson syndrome: severe skin blistering and mucosal involvement.

When prescribing or dispensing Ondansetron, several safety considerations should be observed.

• Cardiac assessment: evaluate patients for existing QT prolongation or electrolyte imbalances before use.
• Drug hypersensitivity: avoid in individuals with known allergy to ondansetron or other 5‑HT3 antagonists.
• Hepatic impairment: use caution and consider dose adjustment in patients with severe liver dysfunction.
• Concomitant QT‑prolonging agents: monitor closely when combined with other medications that affect cardiac repolarisation.
• Pregnancy and lactation: assess risk‑benefit, as safety data are limited; use only if clearly needed.
• Store at room temperature: keep below 25 °C in the original packaging, protect from moisture and light.

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

Major Interactions (Avoid)

• Apomorphine: concurrent use may cause severe hypotension and loss of consciousness.
• Other QT‑prolonging drugs (e.g., quinidine, amiodarone): increase risk of cardiac arrhythmias.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin): may raise ondansetron plasma levels.
• CYP3A4 inducers (e.g., rifampicin, carbamazepine): may reduce drug exposure.
• Dexamethasone: may enhance antiemetic effect, requiring dose adjustment.
• Opioid analgesics: may increase risk of constipation and sedation.