The safety of the asthma drug Xolair is under review to investigate a potential link to cardiovascular problems, Health Canada said Thursday.

The probe was triggered by interim findings in an ongoing U.S. study into the long-term safety of Xolair, known generically as omalizumab.

The early data point to a disproportionate increase in cardiovascular problems among people treated with Xolair compared with those who did not take the drug. The reported problems include heart attacks, abnormal heart rhythms, heart failure, fainting, mini-strokes and blood clots.

"At this time, Health Canada recommends that patients should not stop taking Xolair without first speaking to their doctor," the department said in a statement. "Patients should contact their health care professional if they have any concerns about the medicines they are taking."

In Canada, the drug is indicated to treat asthma in those 12 and older who have moderate to severe persistent asthma, who react to airborne allergens and whose symptoms are not controlled well enough with inhaled corticosteroids.

Health Canada has not concluded there is a link between Xolair and cardiovascular problems, but is assessing the interim findings and working with Novartis Pharmaceuticals Canada to get more information.

If its review raises new safety information, the department said it will inform patients and health care professionals and act if necessary.

The U.S. study, called Evaluating the Clinical Effectiveness and Long-Term Safety in Patients with Moderate to Severe Asthma, or EXCELS, followed about 5,000 patients who use Xolair and a control group of approximately 2,500 people who do not.

Final results of the five-year study are expected in 2012.