The FDA says it has received reports that combinations of the two drugs can alter heart rhythms by prolonging what are known as QT and PR intervals on an electrocardiogram. Prolongation of the QT interval can lead to an abnormal rhythm known as torsades de pointes, while prolongation of the PR interval can lead to a different abnormal rhythm called heart block. In either condition, the patient may experience lightheadedness, fainting or abnormal heart beats. Torsades de pointes can progress to a potentially lethal condition called atrial fibrillation, in which the heart beats so erratically that it can no longer pump blood effectively.
The agency still is investigating the reports and is not yet making recommendations about the drugs. Patients experiencing problems with the drugs should report them to the FDA.
Invirase is marketed by Genentech of
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