Ondansetron Eg (Ondansetron)

Ondansetron Eg is used in the management of nausea and vomiting through its action on serotonin pathways.

• Chemotherapy‑induced nausea and vomiting: helps prevent and control episodes of nausea and vomiting in patients receiving cytotoxic cancer therapy.
• Radiotherapy‑induced nausea and vomiting: reduces the frequency and severity of nausea and vomiting associated with radiation treatment.
• Post‑operative nausea and vomiting: decreases the incidence of nausea and vomiting following surgical procedures.

• Ondansetron selectively blocks serotonin (5‑HT3) receptors located in the chemoreceptor trigger zone of the brain and on vagal afferents of the gastrointestinal tract. By preventing serotonin from binding to these receptors, it interrupts the signaling cascade that initiates the vomiting reflex, thereby reducing nausea and vomiting associated with chemotherapy, radiotherapy, and surgery.

Adverse reactions to ondansetron may vary in frequency and severity.

Common Side Effects

• Headache: mild to moderate pain often described as tension‑type.
• Constipation: reduced bowel movements, sometimes accompanied by abdominal discomfort.
• Diarrhoea: loose stools occurring intermittently.
• Fatigue: a general feeling of tiredness or lack of energy.
• Dizziness: sensation of light‑headedness or unsteadiness.

Serious or Rare Side Effects

• Cardiac arrhythmia: irregular heart rhythm, including QT‑interval prolongation.
• Severe allergic reaction: rash, itching, swelling, or difficulty breathing.
• Serotonin syndrome: agitation, hyperreflexia, tremor, or fever when combined with other serotonergic agents.
• Hepatic dysfunction: elevated liver enzymes indicating possible liver injury.
• Vision changes: blurred vision or sudden loss of vision.
• Blood dyscrasias: neutropenia or thrombocytopenia, though very uncommon.

When prescribing ondansetron, clinicians should consider several safety aspects.

• Cardiac monitoring: assess baseline ECG in patients with known heart disease or electrolyte disturbances.
• Electrolyte balance: correct hypokalaemia, hypomagnesemia, or hypocalcaemia before initiating therapy.
• Concomitant serotonergic drugs: avoid or monitor for serotonin syndrome.
• Pregnancy and lactation: use only if the potential benefit outweighs potential risks.
• Renal or hepatic impairment: dose adjustment may be required based on clinical judgment.
• Store at below 25°C: keep in the original packaging, protect from moisture and direct sunlight.

Ondansetron may interact with several medication classes, requiring attention to avoid reduced efficacy or increased toxicity.

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.

Moderate Interactions (Monitor Closely)

• Other serotonergic agents (SSRIs, SNRIs, tramadol): may raise the risk of serotonin syndrome.
• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): can raise ondansetron plasma levels.
• CYP2D6 inhibitors (e.g., fluoxetine, paroxetine): may modestly increase exposure.
• Diuretics that cause electrolyte loss: may potentiate cardiac effects of ondazol