Ondansetron Eg (Ondansetron)

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

• Chemotherapy‑induced nausea and vomiting: reduces the frequency and severity of acute and delayed episodes.
• Radiation‑induced nausea and vomiting: helps control symptoms during and after radiotherapy.
• Post‑operative nausea and vomiting: decreases the incidence of nausea and vomiting after surgical procedures.
• Pregnancy‑related nausea (hyperemesis gravidarum): provides relief when other therapies are insufficient.

• Ondansetron blocks the serotonin 5‑HT3 receptors located on vagal afferent nerves in the gastrointestinal tract and in the chemoreceptor trigger zone of the brain. By preventing serotonin from binding to these receptors, it interrupts the signaling cascade that initiates the vomiting reflex, thereby reducing nausea and vomiting.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: occasional bowel movement difficulty.
• Diarrhoea: loose stools, usually transient.
• Fatigue: feeling of tiredness or reduced energy.
• Dizziness: light‑headed sensation.
• Injection site pain (if administered intravenously).

Serious or Rare Side Effects

• Cardiac arrhythmia: QT‑interval prolongation that may lead to irregular heart rhythm.
• Severe allergic reaction: rash, itching, swelling, or difficulty breathing.
• Serotonin syndrome: rare condition with agitation, tremor, and hyperreflexia.
• Hepatic dysfunction: elevated liver enzymes indicating liver stress.
• Vision changes: blurred vision or visual disturbances.
• Persistent vomiting despite therapy: may indicate underlying condition progression.

When using Ondansetron, consider the following precautions:

• Cardiac monitoring: patients with known QT prolongation or electrolyte imbalance should be observed.
• Electrolyte assessment: correct potassium, magnesium, or calcium abnormalities before therapy.
• Drug interactions: review concomitant medications that may affect cardiac rhythm.
• Pregnancy and lactation: use only if clearly needed; discuss risks with a healthcare professional.
• 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 can interact with several medicines that influence cardiac rhythm or serotonin pathways.

Major Interactions (Avoid)

• Anti‑arrhythmic agents (e.g., amiodarone, quinidine): may increase QT prolongation risk.
• Certain antipsychotics (e.g., haloperidol, ziprasidone): additive effect on QT interval.
• Serotonergic drugs (e.g., tramadol, linezolide): heightened risk of serotonin syndrome.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may raise ondansetron plasma levels.
• CYP2D6 substrates (e.g., metoprolol, codeine): potential alteration of their metabolism.
• Oral contraceptives: may experience reduced efficacy.
• Antacids containing aluminum or magnesium: can lower oral absorption.
• Diuretics: electrolyte shifts may augment QT‑related risk.