Can Zofran (ondansetron) cause bradycardia?

From the Guidelines

Zofran (ondansetron) can cause bradycardia, although it is considered an uncommon side effect. Ondansetron is primarily used to prevent nausea and vomiting associated with chemotherapy, radiation therapy, and surgery. The medication works by blocking serotonin receptors in the brain and gut, but it can also affect cardiac function in some patients. The risk of bradycardia is higher in patients with pre-existing heart conditions, electrolyte abnormalities (particularly low potassium or magnesium), or in those taking other medications that affect heart rate.

Key Points to Consider

• The typical dosing of ondansetron (4-8 mg orally or intravenously every 8-12 hours) is generally safe, but healthcare providers should monitor patients with cardiac risk factors more closely 1.
• The mechanism behind ondansetron-induced bradycardia involves its effect on cardiac ion channels, particularly potassium channels, which can prolong the QT interval and potentially lead to decreased heart rate.
• Patients experiencing unusual dizziness, lightheadedness, or fainting while taking ondansetron should seek medical attention promptly as these could be signs of bradycardia or other cardiac effects.

Management of Bradycardia

• According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay, atropine remains a first-line treatment for acute symptomatic bradycardia 1.
• However, the provided evidence does not directly link Zofran (ondansetron) to bradycardia, but it is essential to consider the potential risk, especially in patients with pre-existing heart conditions or those taking other medications that affect heart rate.

Recommendations for Healthcare Providers

• Monitor patients with cardiac risk factors closely when prescribing ondansetron.
• Be aware of the potential risk of bradycardia and other cardiac effects associated with ondansetron use.
• Consider alternative medications or adjust the dosing regimen if necessary to minimize the risk of bradycardia.

From the Research

Zofran and Bradycardia

• There is no direct evidence in the provided studies that Zofran (ondansetron) causes bradycardia 2, 3, 4, 5.
• The studies primarily focus on the effectiveness of ondansetron in preventing nausea and vomiting induced by chemotherapy, with no mention of bradycardia as a side effect.
• One study 6 discusses the risk of cardiac arrhythmias associated with ondansetron administration, but it does not specifically mention bradycardia.
• The study 6 found that the current evidence does not support routine ECG and electrolyte screening before single oral ondansetron dose administration to individuals without known risk factors, suggesting that ondansetron is generally safe in terms of cardiac effects.
• However, it is essential to note that the study 6 identified 60 unique reports of arrhythmias associated with ondansetron administration, although the route of administration was predominantly intravenous (80%) and many of these cases involved patients with significant medical history or concomitant use of QT-prolonging medications.

Related Cardiac Effects

• The study 6 highlights the importance of considering the risk of cardiac arrhythmias when administering ondansetron, particularly in patients with pre-existing medical conditions or those taking certain medications.
• While bradycardia is not specifically mentioned, the study's findings suggest that ondansetron may be associated with cardiac effects in certain individuals, and caution should be exercised when prescribing the medication 6.