Ondansetrom Hikma (Ondansetron)

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

• Chemotherapy‑induced nausea and vomiting: reduces the frequency and severity of acute and delayed episodes.
• Postoperative nausea and vomiting: helps prevent nausea after surgical procedures.
• Radiation‑induced nausea and vomiting: alleviates nausea associated with radiotherapy.

• Ondansetron selectively blocks 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, it inhibits the neural signaling cascade that initiates the vomiting reflex, thereby reducing nausea and vomiting triggered by chemotherapeutic agents, radiation, or surgical stimuli. The antagonism is dose‑dependent and provides rapid onset of antiemetic effect within minutes after administration.

Ondansetron may cause a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: reduced bowel movements.
• Diarrhoea: loose stools.
• Fatigue: feeling of tiredness.

Serious or Rare Side Effects

• Cardiac arrhythmia: QT interval prolongation.
• Severe allergic reaction: anaphylaxis or angioedema.
• Serotonin syndrome: agitation, hyperreflexia when combined with serotonergic drugs.

When prescribing Ondansetron, clinicians should consider several safety precautions to minimise risk.

• Cardiac monitoring: assess baseline ECG in patients with known heart disease or electrolyte disturbances.
• Drug interactions: avoid concurrent use with other QT‑prolonging agents when possible.
• Pregnancy: use only if benefits outweigh potential risks; limited data available.
• Lactation: caution as drug is excreted in breast milk; evaluate infant exposure.
• Renal/hepatic impairment: dose adjustment may be required in severe dysfunction.
• Store at ambient temperature: keep below 25 °C, protect from moisture and light in original packaging.

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

Major Interactions (Avoid)

• Antifungal azoles (e.g., ketoconazole): increase QT prolongation risk.
• Certain antiarrhythmics (e.g., amiodarone): additive cardiac effects.
• Other serotonergic agents (e.g., SSRIs, MAOIs): risk of serotonin syndrome.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin): may raise ondansetron plasma levels.
• CYP2D6 substrates (e.g., codeine): reduced analgesic effect.
• Diuretics causing electrolyte imbalance: may predispose to QT changes.