Ondansetron

Ondansetron is an anti-agonist at the 5-HT3 (serotonin) receptor in the:

• area postrema
• afferent vagal nerve terminals in the gut

Ondansetron is as effective an anti-emetic as high-dose metoclopramide but does not have the extra-pyramidal side- effects.

Ondansetron is widely used in the management of acute emesis following cancer chemotherapy.

Currently, four other selective 5HT3-receptor antagonists are licensed for use in the UK - dolasetron, granisetron, palonosetron and tropisetron. All work by the same mechanism and have high affinity and selectivity for the 5HT3 receptor.

Unwanted effects:

• most commonly reported unwanted effects of 5HT3-receptor antagonists are constipation and headache - constipation may be severe
• other unwanted effects are generally mild and transient, including light-headedness, abdominal discomfort, fatigue and asymptomatic rises in liver transaminases
• ECG changes, including prolongation of the QTC interval, have been reported with 5HT3-receptor antagonists - therefore caution is required before prescribing these drugs to patients with pre-existing cardiac conduction defects or a history of cardiac rhythm disturbance

The Summary of Product Characteristics must be consulted before prescribing this drug.

Reference:

1. Drug and Therapeutics Bulletin 2005; 43 (8):57-61.