A Closer Look: Genotypic Resistance Test

Part of A Guide to HIV Drug Resistance

December 2006

Gerald Pierone Jr., M.D., AIDS Research and Treatment Center of the Treasure Coast, Fort Pierce, FL

Patient: Bob S.
Doctor: Gerald Pierone Jr., M.D.
Lowest CD4 count: 20
Highest viral load: 240,000
Current CD4 count: 322
Current viral load: undetectable

These are the genotypic resistance test results for Bob S. (not his real name), a 45-year-old man diagnosed with HIV in 1999. When Bob was first diagnosed, his CD4 count was 20 and his viral load was 240,000. He also was dealing with Mycobacterium avium complex, a serious illness caused by common bacteria.

Gerald Pierone Jr., M.D., started Bob on 3TC, d4T and nevirapine. Bob's CD4 count rose from 20 to 100 and his viral load ranged from 3,000 to 5,000 over the course of the year. These lab results were good, but not good enough. A resistance test in 2000 showed that Bob's HIV had developed resistance to several of his medications, as well as cross-resistance to medications he hadn't even been given yet. Dr. Pierone prescribed a new regimen of 3TC, d4T and the powerful protease inhibitor Kaletra. Bob stayed on this regimen for almost three years, but his CD4 count barely crept up to 200 and his viral load never became undetectable. He had also developed fat loss in his face and peripheral neuropathy, a painful, burning sensation in his extremities.

Article Toolbox

So, in June 2004, Dr. Pierone did a genotypic resistance test. This test suggested resistance to all of the available protease inhibitors except for atazanavir (Reyataz). Bob's HIV was also sensitive to tenofovir. The best solution, Dr. Pierone decided, was to prescribe a four-drug regimen of 3TC, atazanavir, ritonavir (Norvir) and tenofovir. However, despite this switch, Bob's viral load remained in the 1,000 to 2,000 range and his CD4 count didn't move from 200.

In July 2005, another resistance test showed that Bob's HIV was sensitive to tipranavir (Aptivus), which had recently been approved. So, in October 2005, Bob was switched to Truvada (a combination of FTC and tenofovir), ritonavir and tipranavir. Soon after, for the first time, Bob's viral load dropped to an undetectable level and his CD4 count climbed to 322, higher than it's ever been. In addition, Bob's peripheral neuropathy has completely resolved and his facial thinning has improved.