The U.S. Food and Drug Administration announced that new safety information has been added to the label for the HIV antiviral drug Invirase (saquinavir), describing potentially life-threatening side effects on the heart when used with Norvir (ritonavir), another HIV antiviral medication. In February 2010, the agency warned patients and health care professionals that when used together, the two drugs could cause prolongation of the QT and PR intervals--indicators of heart rhythm activity seen on an electrocardiogram... 
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