A drug prescribed to prevent nausea and vomiting in cancer and surgery patients may change the electrical activity of the heart, Health Canada warns.

The 32 milligram intravenous dose of Zofran should not be used, the regulator said Tuesday in announcing a new maximum recommended dose of 16 milligrams.

si-heart-monitor-220-cp-rtr

The heart's QT interval is read from an electrocardiogram and is an indicator of how the organ electrically resets itself after each beat. (Reuters)

"A recent study showed that Zofran can affect the "QT interval" (a measure of the heart's electrical activity) when used at high doses," Health Canada said in an advisory to patients.

"When the QT interval is too long, abnormal heart beats can arise, which could result in dizziness, a sensation of rapid, pounding, or irregular heartbeat, fainting or death."

Zofran, also called ondansetron hydrochloride dihydrate or ondansetron, is given to prevent nausea and vomiting in patients receiving chemotherapy and radiation for cancer, and in patients who have had surgery.

Health Canada said there were no recommended dosing changes when the drug is given by mouth to adults or for children taking it intravenously or by mouth.

People taking Zofran are advised to tell their doctor immediately if they experience dizziness, abnormal heartbeat, or fainting during treatment with the drug.

GlaxoSmithKline sent a letter to healthcare professionals to inform them of the new safety information.