Ondansetron
Ondansetron is a 5-HT3 receptor antagonist used to prevent nausea and vomiting. Its label indicates it for prevention of postoperative nausea and vomiting among other uses, and the facts most worth knowing are about the heart rhythm and about what it is combined with.
Key points
- Ondansetron is indicated for the prevention of postoperative nausea and vomiting.
- The label directs avoiding ondansetron in patients with congenital long QT syndrome, because of QT interval prolongation and torsade de pointes.
- Where there are concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or other QT-prolonging drugs, ECG monitoring is directed.
- Concomitant use of apomorphine is a contraindication.
How it works
Ondansetron blocks 5-HT3 receptors, interrupting one of the signalling routes that produces nausea and vomiting. That serotonergic action is also the reason for the serotonin syndrome caution below, so the mechanism and the interaction warning are the same fact seen from two sides.
Safety specific to ondansetron
QT prolongation and torsade de pointes. The label directs avoiding ondansetron in patients with congenital long QT syndrome, and monitoring with electrocardiograms where there are concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or use of other QT-prolonging drugs.
The electrolyte clause matters more than it looks in a medicine given for vomiting: prolonged vomiting is itself a cause of electrolyte disturbance, so the situation that prompts the prescription can be the situation that raises the risk.
Apomorphine. Concomitant use of apomorphine is contraindicated.
Serotonin syndrome. This has been reported with 5-HT3 receptor antagonists alone, but particularly with concomitant use of serotonergic drugs. That group includes many antidepressants, which is a common combination when nausea is being treated in someone already on long-term medication.
When to seek urgent care
Palpitations, fainting or a sensation of the heart racing while taking ondansetron warrant urgent assessment. So do agitation, confusion, fever, shivering, muscle twitching or rigidity, which are the features of serotonin syndrome.