Ondansetron Eg (Ondansetron Hydrochloride Dihydrate)

Ondansetron Eg is a selective 5‑HT3 receptor antagonist used in the antiemetic pathway to control nausea and vomiting.

• Chemotherapy‑induced nausea and vomiting: prevents and reduces nausea and vomiting caused by cytotoxic chemotherapy.
• Radiotherapy‑induced nausea and vomiting: prevents nausea and vomiting that occur during or after radiation therapy.
• Postoperative nausea and vomiting: reduces the incidence and severity of nausea and vomiting following surgical procedures.

• Ondansetron acts by selectively antagonizing serotonin (5‑HT3) receptors located in the chemoreceptor trigger zone of the brain and in peripheral vagal afferents of the gastrointestinal tract. By blocking these receptors, it inhibits the transmission of emetic signals, thereby diminishing the central and peripheral pathways that trigger nausea and vomiting.

Common Side Effects

• Headache: mild to moderate headache may occur after administration.
• Constipation: reduced bowel motility leading to hard stools.
• Dizziness: transient sensation of light‑headedness.
• Injection site reactions: pain, erythema, or swelling at the site of intramuscular or intravenous administration.

Serious or Rare Side Effects

• QT interval prolongation: may lead to cardiac arrhythmias, especially in patients with electrolyte disturbances.
• Severe allergic reactions: anaphylaxis or angioedema requiring immediate medical attention.
• Serotonin syndrome: rare but potentially life‑threatening condition when combined with other serotonergic agents.
• Hypotension: sudden drop in blood pressure, particularly with rapid intravenous injection.

Before initiating therapy, clinicians should consider the following precautions:

• Cardiac assessment: evaluate baseline QT interval and correct electrolyte imbalances to reduce arrhythmia risk.
• Hepatic function: adjust use in patients with severe liver impairment as metabolism may be reduced.
• Concomitant QT‑prolonging drugs: avoid or monitor closely when used with other agents that affect cardiac repolarization.
• Hypersensitivity: discontinue if signs of allergic reaction such as rash, itching, or swelling develop.
• Pregnancy and lactation: use only if the potential benefit justifies the potential risk to the fetus or infant.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake the solution.

Ondansetron may interact with several medications that affect its safety or efficacy.

Major Interactions (Avoid)

• Apomorphine: concurrent use can cause severe hypotension and loss of consciousness.
• Other QT‑prolonging agents (e.g., quinidine, amiodarone, sotalol): may increase the risk of cardiac arrhythmias.
• Carbamazepine: induces metabolism of ondansetron, potentially reducing its antiemetic effect.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may raise ondansetron plasma concentrations.
• CYP2D6 inhibitors (e.g., fluoxetine, paroxetine): can modestly increase drug levels.
• Anesthetic agents (e.g., propofol, volatile anesthetics): may augment QT prolongation, requiring ECG monitoring.