Not all antiretrovirals (ARVs) effectively penetrate the brain. What's more, studies have found that HIV can continue to reproduce in the brain, even when HIV levels are undetectable in the blood, potentially leading to HIV-related brain disorders like dementia.  

Scott Letendre, MD, of the school of medicine at the University of California in San Diego, and his colleagues treated ten HIV-positive patients with Kaletra alone for three weeks and then added at least two other ARVs. They measured HIV levels in the blood and the cerebrospinal fluid (CSF)—a measure of how well the drug controlled HIV in the brain—after three, 12 and 24 weeks.

At the third week, all ten patients had reductions in viral load in their CSF. Of the eight patients who continued to the end of the study, all had undetectable viral loads in both the blood and CSF at week 24. The researchers conclude that Kaletra does appear to reach the brain at high enough levels to shut down HIV reproduction.