The FDA ( Food and Drug Administration ) has informed the public of an ongoing safety review of the anti-nausea drug Zofran ( Ondansetron ).
Ondansetron may increase the risk of developing abnormal changes in the electrical activity of the heart, which can result in a potentially fatal abnormal heart rhythm.

Zofran is used to prevent nausea and vomiting caused by cancer chemotherapy, radiation therapy and surgery.
Is in a class of medications called 5-HT3 receptor antagonists. Works by blocking the action of serotonin, a natural substance that may cause nausea and vomiting.
Available as 4 mg and 8 mg tablets, 4 mg and 8 mg orally disintegrating tablets, and oral solution ( 4 mg/5 mL ). Also available as an injection for intravenous use ( 2 mg/mL ).

Changes in the electrical activity of the heart ( prolongation of the QT interval of the electrocardiogram [ ECG ] ) can lead to an abnormal and potentially fatal heart rhythm ( including torsade de pointes ). Patients at particular risk for developing torsade de pointes include those with underlying heart conditions, such as congenital long QT syndrome, those who are predisposed to low levels of potassium and magnesium in the blood, and those taking other medications that lead to QT prolongation.

FDA has reviewed all available information and is making interim changes to the drug labels. The manufacturer of Zofran ( GlaxoSmithKline ) is being required to conduct a thorough QT study to assess the potential for the drug to prolong the QT interval. The results from this study are expected to be available in the summer of 2012. Additional label changes may result after the additional information has been reviewed.

The Zofran drug labels already contain information about the potential for QT prolongation. The labels are being revised to include a warning to avoid use in patients with congenital long QT syndrome because these patients are at particular risk for torsade de pointes. Additionally, recommendations for ECG monitoring in patients with electrolyte abnormalities ( e.g., hypokalemia or hypomagnesemia ), congestive heart failure, bradyarrhythmias, or in patients taking other medications that can lead to QT prolongation, are being included in the labels.

Source: FDA, 2011

XagenaMedicine2011