FDA warns of coupling Invirase/Norvir after abnormal heart rhythms found
The FDA has added additional information to the warning label of the antiviral drug saquinavir (Invirase, Genentech), after the agency found that electrical activity of the heart can change when the drug is used in conjunction with ritonavir (Norvir, Abbott Laboratories), another antiviral medication.

Saquinavir and ritonavir are administered together as a treatment for HIV. Changes in the heart’s electrical activity could lead to abnormal heart rhythms—QT or PR intervals—that could cause the potentially fatal abnormal rhythm torsades de points to occur.

The information was brought forth after a clinical trial, initiated in February 2010, found the potential risk of adverse effects when the combination of drugs is used. The trial, evaluating 59 patients, showed that PR interval prolongation of over 200 msec was observed in 40 percent and 47 percent of the patients who received Invirase/Norvir 1000/100 mg twice daily and 1500/100 mg twice daily, respectively.

The FDA has added the aforementioned information to the Warnings and Precautions, Contraindications and Clinical Pharmacology sections of Invirase.

The FDA recommends that physicians perform an electrocardiogram prior to administering this treatment to patients, particularly who are diagnosed with another heart condition or who already have heart rate/rhythm problems. Additionally, patients will be required to pick up a medication guide when picking up Invirase prescriptions, which will outline the added information.

Back in Feburary, the FDA warned physicians about the drug's potential to change the electrical activity of the heart and had said that it would continue to review the collected data from the clinical trial.