FDAnews Drug Daily Bulletin

Physician labeling for Abbott Laboratories’ protease inhibitor Norvir has been updated to include a new precaution for patients with cardiac disease regarding a disturbance of heart rhythm or atrioventricular (AV) block called PR prolongation.

AV block, or heart block, is a condition in which electrical signals from the heart’s upper and lower chambers are either partially or completely blocked. The condition is classified as first, second or third degree. Third-degree AV block requires that a pacemaker be implanted to prevent cardiac arrest.

The label change is the result of a heart rhythm study that Abbott conducted at the request of the FDA, Abbott said. The agency has made the same request of other HIV-drug manufacturers, according to the company.

“Postmarketing cases of second- or third-degree [AV] block have been reported in patients,” the new precaution states. “Norvir [ritonavir] should be used with caution in patients with underlying structural heart disease, preexisting conduction system abnormalities, ischemic heart disease, [and] cardiomyopathies, as these patients may be at increased risk for developing cardiac conduction abnormalities.”

The new precaution, which applies to the soft gelatin capsules and oral solution formulations of the product, also says that administering the HIV drug with other drugs that prolong the PR interval — including Bristol-Myers Squibb’s protease inhibitor Reyataz (atazanavir sulfate) — has not been evaluated for PR prolongation and needs to be done with caution, particularly with drugs metabolized by the CYP3A pathway.