ondansetron: clinical use

Prescribing considerations

• Assess QT-prolongation risk, cardiac disease, bradyarrhythmia, electrolyte disturbance and concurrent QT-prolonging medicines.
• Correct hypokalaemia and hypomagnesaemia before administration.
• Clearance is substantially reduced in moderate or severe hepatic impairment.
• Consider constipation and monitor patients with signs of subacute intestinal obstruction.
• Ondansetron may mask bleeding after adenotonsillar surgery.
• Observe for serotonin syndrome when combined with serotonergic medicines.

Contraindications and cautions

• Concomitant apomorphine.
• Hypersensitivity to ondansetron or product excipients.
• For Setofilm, hypersensitivity to another selective 5-HT3 antagonist.
• Avoid in congenital long-QT syndrome.

Monitoring

• ECG when clinically indicated by cardiac history, interacting medicines or electrolyte disturbance.
• Electrolytes in patients at risk of depletion.
• Bowel function where obstruction or severe constipation is suspected.
• Hepatic function in children receiving hepatotoxic chemotherapy.
• Clinical features of serotonin syndrome with serotonergic combinations.

Clinical pharmacology

A potent, selective 5-HT3 receptor antagonist acting on peripheral vagal pathways and central vomiting pathways. Oral absorption is rapid; clearance occurs mainly through hepatic metabolism involving CYP3A4, CYP2D6 and CYP1A2.

Formulation and product differences

• The orodispersible tablet disperses on the tongue and contains aspartame, which requires consideration in phenylketonuria.
• Setofilm is an individually wrapped orodispersible film that dissolves without water and may help people who have difficulty swallowing tablets.
• Setofilm should be handled with dry fingers, used only if undamaged and not divided to create a smaller strength.

Dispersible tablet

Route: Oral

Strengths: 4 mg, 8 mg