Kaletra (lopinavir/ritonavir) can significantly increase blood levels of Crestor (rosuvastatin)—one of the most effective drugs used to lower high cholesterol—say researchers of a study published in the Journal of Acquired Immune Deficiency Syndromes. This was an unexpected finding, as Crestor is not metabolized significantly through the liver pathway that Kaletra, and other protease inhibitors, are known to affect.

Jennifer Kiser, Pharm D, from the department of pharmaceutical sciences at the University of Colorado in Denver, and her colleagues enrolled 20 HIV-negative men and women to assess the impact of Kaletra on Crestor blood levels. The study volunteers agreed to first take 20mg of Crestor alone for seven days, then Kaletra alone for 10 days, and finally a combination of the two drugs for seven additional days. A full set of data were available on 15 of the volunteers.

Kiser’s team found that Kaletra had a significant impact on Crestor blood levels.  The total area under the curve—which measures the sum of the blood levels over time—was two times higher when Kaletra was taken with Crestor, compared with values when Crestor was taken alone. Even more significant, the peak dose of Crestor, which can impact side effects, was nearly five times higher when the two drugs were taken together. Though the severity of side effects in the study volunteers was reported as mild or moderate, it is possible that persistently high levels of Crestor in people with HIV who are also taking Kaletra may lead to more serious side effects.

The metabolism pathway responsible for the increased blood levels of Crestor could not be determined by Kiser’s team. Rather, they are calling for additional studies that combine Crestor with a number of different protease inhibitors to identify the reasons behind this drug interaction, and to determine whether a lower dose of Crestor when taken with Kaletra may be safe and effective.