The FDA ( Food and Drug Administration ) is reviewing clinical trial data about a potentially serious effect on the heart from the use of Invirase ( Saquinavir ) in combination with Norvir ( Ritonavir ). The data suggest that together the two drugs may affect the electrical activity of the heart.

The changes to the electrical activity of the heart possibly associated with these drugs, known as prolonged QT or PR intervals, can be seen on an electrocardiogram ( EKG ). A prolonged QT interval can increase the risk for abnormal heart rhythms, including a serious abnormal rhythm called torsades de pointes. A prolonged PR interval can cause the electrical signal responsible for generating a heart beat to slow or even stop; this is known as heart block and can affect how fast the heart is able to beat.

Saquinavir and Ritonavir are antiviral medications given together to treat HIV infection. Ritonavir is given at a low dose with Saquinavir in order to increase the level of Saquinavirin the body. This is a process known as boosting.

FDA's analysis of these data is ongoing. However, healthcare professionals should be aware of this potential risk for changes to the electrical activity of the heart. Invirase and Norvir should not be used in patients already taking medications known to cause QT interval prolongation such as Class IA ( such as Quinidine ) or Class III ( such as Amiodarone ) antiarrhythmic drugs; or in patients with a history of QT interval prolongation.

Patients should not stop taking their prescribed antiviral medications. Patients who are concerned about possible risks associated with using Invirase and Norvir should talk to their healthcare professional.

The study data were submitted by Roche, the manufacturer of Invirase, based on FDA's request that all manufacturers of protease inhibitors, including Invirase, conduct a thorough QT study to evaluate the effect these drugs have on the QT and PR intervals.
The preliminary data has shown that when Invirase boosted with Norvir ( 1000 mg / 100 mg) was given to healthy patients, ages 18 to 55 years, there was a dose-dependent prolongation of the QT and PR intervals. The magnitude of the effect and clinical implications of QT and PR interval prolongation are still being reviewed by FDA.

These findings suggest that some patients using Invirase boosted with Norvir may be at an increased risk for developing abnormal heart rhythms. In particular, this risk may be increased in patients using other medications known to cause QT interval prolongation such as Class IA and Class III antiarrhythmic drugs or in patients with a history of QT interval prolongation.

Source: FDA, 2010

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