Ondansetrón Teva-Ratio (Ondansetron)

Ondansetron is employed across several clinical pathways that involve emesis control.

• Chemotherapy‑induced nausea and vomiting (CINV): reduces the frequency and severity of acute and delayed episodes.
• Radiotherapy‑induced nausea and vomiting (RINV): helps maintain patient comfort during and after radiation treatment.
• Post‑operative nausea and vomiting (PONV): lowers the incidence of nausea and vomiting after surgical procedures.
• Pregnancy‑associated nausea (hyperemesis gravidarum): provides relief when other measures are insufficient.

• Ondansetron selectively 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 inhibiting this receptor, it prevents serotonin‑mediated stimulation of the vomiting centre, thereby reducing nausea and vomiting triggered by chemotherapy, radiation, surgery or other emetogenic stimuli.

Side‑effect profiles reflect the drug’s pharmacology and patient variability.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: occasional bowel habit changes.
• Diarrhoea: transient loose stools.
• Fatigue: general tiredness.
• Dizziness: brief episodes of light‑headedness.

Serious or Rare Side Effects

• QT‑interval prolongation: may predispose to cardiac arrhythmias.
• Severe hypersensitivity: rash, itching, swelling or anaphylaxis.
• Serotonin syndrome: rare when combined with other serotonergic agents.
• Hepatic enzyme elevation: abnormal liver function tests.
• Neuroleptic malignant‑like reactions: extremely uncommon but serious.

When prescribing Ondansetron, clinicians should consider several safety aspects.

• Cardiac monitoring: assess baseline ECG in patients with known QT prolongation.
• Electrolyte balance: correct hypokalaemia, hypomagnesaemia or hypocalcaemia before use.
• Concomitant serotonergic drugs: evaluate risk of serotonin syndrome.
• Pregnancy: weigh benefits against potential risks; use only if clearly needed.
• Renal/hepatic impairment: dose adjustment may be required based on clinical judgment.
• Store at ambient temperature: keep in the original container, protect from moisture and direct sunlight.

Ondansetron may interact with several medicines that influence cardiac rhythm or serotonergic pathways.

Major Interactions (Avoid)

• Anti‑arrhythmic agents (e.g., amiodarone, quinidine): increase risk of QT prolongation.
• Certain antipsychotics (e.g., haloperidol, ziprasidone): additive effect on cardiac repolarisation.

Moderate Interactions (Monitor Closely)

• Selective serotonin reuptake inhibitors (SSRIs) and serotonin‑norepinephrine reuptake inhibitors (SNRIs): potential for serotonin syndrome.
• Tramadol and other opioids: heightened serotonergic activity.
• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin): may raise ondansetron plasma levels.
• CYP2D6 substrates (e.g., metoprolol, codeine): altered metabolism may occur.