Norvir (ritonavir)—when given at the type of low doses used to boost blood levels of other protease inhibitors—does not affect how the body uses insulin, according to a study published online June 30 in the Journal of Acquired Immune Deficiency Syndromes.

Full-dose Norvir was once considered among the most potent of the available protease inhibitors. Unfortunately, when it is taken at 800 milligrams (mg) per day, as it was in the late 1990s, it causes significant side effects, such as lowering the body's ability to use insulin properly. This condition, called insulin resistance, can ultimately lead to diabetes, which in turn can increase the risk of cardiovascular disease.

Fortunately, Norvir is no longer used at the original dose. Rather, most people take only 200 mg per day in order to boost the blood levels of other protease inhibitors. What has remained unknown, however, is whether this lower dose might affect insulin in ways similar to the higher dose.

The answer that question, Steven Taylor, MD, from the University of California at San Francisco, and his colleagues, tested the level of insulin resistance in HIV-negative volunteers after they took a single dose of 200 mg of Norvir, and compared this with people taking a placebo.

Taylor's group found that people taking Norvir were no more likely to have changes in their insulin or blood sugar than people taking a placebo. “Consideration should be given to these findings when assessing the metabolic effects of antiretroviral regimens and advising patients,” the authors conclude.