From the Guidelines
Zofran (ondansetron) should not be administered to patients with known hypersensitivity to ondansetron or other 5-HT3 receptor antagonists, as well as those taking apomorphine due to reports of profound hypotension and loss of consciousness when used together. The primary concern with ondansetron administration is its potential to cause QT prolongation, which can lead to life-threatening arrhythmias such as Torsades de Pointes 1. This risk is particularly elevated in patients with congenital long QT syndrome or those taking other medications that can prolong the QT interval.
Key Considerations
- Patients with liver impairment should receive reduced dosing due to decreased clearance of the medication.
- Ondansetron should be used cautiously during pregnancy, particularly in the first trimester, as some studies suggest a small increased risk of oral clefts.
- Patients with phenylketonuria should be aware that some formulations contain phenylalanine.
- Ondansetron may mask symptoms in patients with progressive ileus or gastric distention, so it should be used with caution in these conditions.
Mechanism and Alternatives
The medication works by blocking serotonin receptors in the chemoreceptor trigger zone and gastrointestinal tract, preventing nausea and vomiting signals from reaching the vomiting center in the brain. Alternative antiemetic strategies, including the use of dopamine antagonists, corticosteroids, and neurokinin-1 receptor antagonists, may be considered based on patient risk factors and the type of surgery or treatment being undertaken 1.
From the FDA Drug Label
Ondansetron tablets are contraindicated in patients: known to have hypersensitivity (e. g., anaphylaxis) to ondansetron or any of the components of the formulation [see Adverse Reactions (6.2)]. receiving concomitant apomorphine due to the risk of profound hypotension and loss of consciousness.
The contraindications for administering Zofran (ondansetron) are:
- Hypersensitivity to ondansetron or any of the components of the formulation
- Concomitant use of apomorphine due to the risk of profound hypotension and loss of consciousness 2
From the Research
Contraindications for Administering Zofran (Ondansetron)
The following are contraindications for administering Zofran (ondansetron):
- Congenital long QT syndrome, as ondansetron can prolong the QT interval and increase the risk of ventricular dysrhythmias 3, 4, 5, 6
- Hypokalemia and hypomagnesemia, as these conditions can increase the risk of QT prolongation and torsades des pointes 6
- Use of other QT-prolonging agents, as concomitant use can increase the risk of ventricular dysrhythmias 3, 6
- Patients with a history of ventricular dysrhythmias or cardiac arrest, as ondansetron can increase the risk of these events 6
Special Considerations
- Patients with occult QT prolongation are at risk of experiencing malignant dysrhythmias when ondansetron is administered, especially in conjunction with anesthetic agents that also prolong the QT interval 3
- The incidence of congenital QT prolongation in the general population has been estimated to be 1:2,500, and it may be undiagnosed preoperatively, especially in pediatric patients 3
- A single intravenous dose of ondansetron can induce QT prolongation in adult emergency department patients, and the risk is higher with 8 mg doses compared to 4 mg doses 5