Ondansetron B. Braun (Ondansetron)

Ondansetron acts on the serotonin‑mediated pathway that triggers nausea and vomiting. It is indicated for:

• Chemotherapy‑induced nausea and vomiting: reduces incidence and severity of nausea and vomiting in patients receiving cytotoxic chemotherapy.
• Radiotherapy‑induced nausea and vomiting: helps control nausea and vomiting associated with radiation treatment.
• Postoperative nausea and vomiting: prevents nausea and vomiting after surgical procedures.

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

Common Side Effects

• Headache: mild to moderate headache may occur.
• Constipation: reduced bowel movements are frequently reported.
• Dizziness: transient light‑headedness can be experienced.
• Fatigue: patients may feel unusually tired.
• Injection site reaction: redness, pain or swelling at the IV site.
• Diarrhoea: occasional loose stools.

Serious or Rare Side Effects

• QT interval prolongation: may predispose to cardiac arrhythmias.
• Severe allergic reaction (anaphylaxis): rare but potentially life‑threatening.
• Serotonin syndrome: risk when combined with other serotonergic agents.
• Cardiac arrhythmia: rare cases of ventricular tachycardia.
• Hypotension: sudden drop in blood pressure in susceptible individuals.
• Hepatic dysfunction: very rare liver enzyme elevations.

Before initiating therapy, consider the following precautions:

• Cardiac risk assessment: evaluate baseline ECG for QT prolongation.
• Electrolyte monitoring: correct hypokalaemia or hypomagnesaemia that can exacerbate QT issues.
• Pregnancy safety: use only if clearly needed; category B indicates no proven risk in animal studies.
• Hepatic function: dose adjustment may be required in severe liver impairment.
• Concomitant QT‑prolonging drugs: avoid or monitor closely when used together.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Ondansetron may interact with several drug classes.

Major Interactions (Avoid)

• Apomorphine: concurrent use can cause severe hypotension and loss of consciousness.
• Other 5‑HT3 antagonists: additive antiemetic effect may increase risk of cardiac events.
• QT‑prolonging agents (e.g., quinidine, amiodarone): combined use can markedly lengthen QT interval.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may increase ondansetron plasma levels.
• CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce efficacy by lowering drug concentrations.
• Opioids and anticholinergics: may enhance sedation or constipation, requiring clinical observation.