Onda (Ondansetron)

Ondansetron is used to control nausea and vomiting that arise from several therapeutic pathways.

• Chemotherapy‑induced nausea and vomiting: reduces the frequency and severity of acute and delayed episodes.
• Radiotherapy‑induced nausea and vomiting: helps maintain patient comfort during and after treatment.
• Post‑operative nausea and vomiting: decreases the need for rescue anti‑emetics after surgery.
• Pregnancy‑related hyperemesis gravidarum: provides relief when other measures are insufficient.
• Anticipatory nausea: lessens conditioned nausea in patients with a history of severe chemotherapy‑induced vomiting.

• 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 effects are generally mild but can vary in frequency and severity.

Common Side Effects

• Headache: mild to moderate intensity.
• Constipation: occasional bowel habit changes.
• Diarrhoea: transient loose stools.
• Fatigue: feeling of tiredness.
• Dizziness: light‑headed sensation.

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 dysfunction: elevated liver enzymes in susceptible individuals.
• Neuroleptic malignant‑like reactions: extremely rare but potentially life‑threatening.

Before prescribing Ondansetron, clinicians should assess patient‑specific risk factors and follow safe handling practices.

• Cardiac monitoring: avoid in patients with known prolonged QT interval or electrolyte disturbances.
• Electrolyte balance: correct hypokalaemia, hypomagnesaemia or hypocalcaemia before use.
• Hepatic impairment: dose adjustment may be required in moderate to severe liver disease.
• Concomitant serotonergic drugs: monitor for signs of serotonin syndrome.
• Pregnancy and lactation: use only if benefit outweighs potential risk.
• Store at ambient temperature: keep below 25 °C, retain original packaging and protect from moisture.

Ondansetron may interact with several medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Apomorphine: concurrent use can cause profound hypotension and loss of consciousness.
• Certain anti‑arrhythmic agents (e.g., amiodarone, quinidine): increase risk of QT prolongation.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., erythromycin, ketoconazole): may raise ondansetron plasma levels.
• CYP2D6 substrates (e.g., codeine, tramadol): potential for altered analgesic effect.
• Serotonergic agents (e.g., SSRIs, MAOIs): monitor for serotonin syndrome.
• Diuretics causing electrolyte loss: watch for QT‑related cardiac events.