The patient package insert has been updated, as well, with language related to electrocardiogram changes and cardiac arrhythmias.

The following information was added to the product label:
Under Clinical Pharmacology –
QTcF interval was evaluated in a randomized, placebo and active (moxifloxacin 400 mg once-daily) controlled crossover study in 45 healthy adults, with 10 measurements over 12 hours on Day 3. The maximum mean (95% upper confidence bound) time-matched difference in QTcF from placebo after baseline correction was 5.5 (7.6) milliseconds (msec) for 400 mg twice-daily ritonavir.  Ritonavir 400 mg twice daily resulted in Day 3 ritonavir exposure that was approximately 1.5 fold higher than observed with ritonavir 600 mg twice-daily dose at steady state.  
PR interval prolongation was also noted in subjects receiving ritonavir in the same study on Day 3.  The maximum mean (95% confidence interval) difference from placebo in the PR interval after baseline correction was 22 (25) msec for 400 mg twice-daily ritonavir.  See PRECAUTIONS –PR Interval Prolongation.

Under Precautions –
PR Interval Prolongation
Ritonavir prolongs the PR interval in some patients. Postmarketing cases of second or third degree atrioventricular block have been reported in patients.

NORVIR should be used with caution in patients with underlying structural heart disease, preexisting conduction system abnormalities, ischemic heart disease, cardiomyopathies, as these patients may be at increased risk for developing cardiac conduction abnormalities.
The impact on the PR interval of co-administration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers, beta-adrenergic blockers, digoxin and atazanavir) has not been evaluated. As a result, co-administration of ritonavir with these drugs should be undertaken with caution, particularly with those drugs metabolized by CYP3A. Clinical monitoring is recommended. See CLINICAL PHARMACOLOGY - Effects on Electrocardiogram.

Under Information for Patients -
Cardiovascular System
First –degree AV block, second-degree AV block, third-degree AV block, right bundle branch block have been reported (See PRECAUTIONS – PR Interval Prolongation).

Under Adverse Reactions –
Cardiovascular System
First –degree AV block, second-degree AV block, third-degree AV block, right bundle branch block have been reported (See PRECAUTIONS – PR Interval Prolongation).

In addition, the following information has been added to the Patient Product Insert, under the section What are the Possible Side Effects of Norvir? –
Changes in the electrocardiogram (EKG). Consult your physician if you experience dizziness, lightheadedness, fainting spells or abnormal heart beat, Patients with heart defects or conduction defects should avoid NORVIR.

The complete, revised label is available on the FDA website at Drugs@FDA  (http://www.accessdata.fda.gov/scripts/cder/drugsatfda/)

Richard Klein
Office of Special Health Issues
Food and Drug Administration

Kimberly Struble
Division of Antiviral Drug Products
Food and Drug Administration