Pharm 101: Ondansetron

Class

Anti-emetic

Pharmacodynamics

• 5-HT3 receptor antagonist with peripheral and central actions
• Works mainly via blockade of peripheral 5-HT3 receptors on extrinsic vagal and spinal afferent nerves
• Some effect on central 5-HT3 receptors in chemoreceptor trigger zone (CTZ) and vomiting centre
• Anti-emetic action is restricted to emesis due to vagal stimulation and chemotherapy. Little effect on other emetic stimuli such as motion sickness

Pharmacokinetics

• Half life 4-9 hours
• Extensive hepatic metabolism
• Renal and hepatic excretion (dose reduction is required for hepatic insufficiency)

Clinical uses

• Prevention of chemotherapy-induced nausea and vomiting
• Treatment and prevention of post-operative and post-radiation nausea and vomiting

Adverse effects

• Most common are headaches, dizziness, constipation
• Prolongation of QT interval
• Serotonin syndrome if taken with other serotonergic drugs

Precautions/contraindications

• Hepatic failure
• Caution in patients with prolonged QT, especially in conjunction with other medications that may prolong QT interval

Further Reading

• Cadogan M. Serotonin Toxicity