The U.S. Food and Drug Administration said Tuesday that preliminary data suggests taking Invirase and Norvir together may affect electrical activity in the heart.

People taking a combination of two anti-HIV drugs may face potential heart risks, U.S. regulators say.

Invirase and Norvir are antiviral medications given together to treat HIV infection. Norvir is given at a low dose to boost the level of Invirase in the body.

The U.S. Food and Drug Administration said Tuesday that preliminary data suggests taking Invirase and Norvir together may affect electrical activity in the heart.

Both drugs are approved for use in Canada.

The FDA advised patients currently taking Invirase that they should not stop taking the drug, but to discuss any questions or concerns they have about Invirase with their doctors.

As well, the FDA said patients should review their cardiovascular medical history and current medications with their doctors to determine if they should continue using Invirase, and report any side-effects.

FDA's preliminary analysis of clinical trial data from Invirase's manufacturer, Roche, suggests the drug combination can lead to irregular heart rhythms that can cause lightheadedness, fainting and in some cases death.

The heart rhythm problem occurred in healthy patients aged 18 to 55 who were taking 1,000 mg of Invirase boosted with 100 mg of Norvir. The side-effects depended on the dose, FDA said.

The FDA is still reviewing the magnitude of the effects and their clinical implications.