Arrhythmia Risk Leads to Label Change for Zofran

Interim data from a recent clinical trial has indicated that a 32 mg single dose of Zofran® (ondansetron) may affect the electrical activity of the heart and could predispose patients to develop an abnormal heart rhythm. The U.S. Food and Drug Administration (FDA) has released a drug safety communication and GlaxoSmithKline, the manufacturer, has responded accordingly by changing the dosage labeling on the drug.

Zofran is an anti-nausea drug that is part of a class of drugs called 5-HT3 receptor antagonists. These drugs—sometimes referred to as antiemetics—are designed to block one or more of the signals that cause nausea and vomiting. Zofran is used in a variety of different ways in order to prevent the nausea and vomiting associated with chemotherapy, radiation therapy, and surgery.

Zofran will continue to be used in adults and children who are experiencing nausea and vomiting—but at lower doses. The updated label removes the 32 mg single intravenous dose, but does not change any of the recommended oral dosing regimens or the recommended lower intravenous dosing of the drug. In fact, the updated label indicates that Zofran is still safe at the lower recommended intravenous dose of 0.15 mg/kg administered every 4 hours for 3 doses. No single intravenous dose should exceed 16 mg.

The updated label comes after preliminary results from a recent clinical trial indicated that a 32 mg single intravenous dose of Zofran could affect the electrical activity of the heart, resulting in a condition called QT interval prolongation, which could predispose patients to a potentially fatal arrhythmia condition called Torsades de Pointes.

The FDA will evaluate the final data from the study when it becomes available and work with the manufacturer to identify a safe, effective single-dose regimen.


FDA Drug Safety Communication: New information regarding QT prolongation with ondansetron (Zofran). June 29, 2012. U.S. Food and Drug Administration website. Available at:

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