Study says complete adherence to an anti-HIV regimen best avoids drug resistance

A study in the February 1 issue of the Journal of Infectious Diseases and presented Thursday at an American Medical Association briefing shows that complete adherence to an HIV antiretroviral drug regimen is the best way to prevent HIV from mutating and developing resistance to the medications. Researchers at Canada's British Columbia Centre for Excellence in HIV/AIDS studied nearly 1,200 HIV-positive people who began antiretroviral therapy between 1996 and 1999 and took the medications for at least three years. Nearly 300 people developed drug resistance during the first 2.5 years of treatment, with little differences in the onset of drug resistance seen between study subjects on a protease inhibitor-based regimen and a nonnucleoside reverse transcriptase inhibitor-based regimen. Patients who took all of their pills on time were the least likely to developed drug resistance, the researchers report. Study subjects who took only about 80% of their medications as prescribed were shown to be four times more likely to develop drug resistance than those who took all of their pills on time or missed just 5% or less of their medications. Missed medication doses can result in low concentrations of the drugs in the bloodstream and less than optimal suppression of the virus, which in turn allows HIV to mutate and develop resistance to the medications. "The results prove HIV drug regimens are nothing like a game of horseshoes--close is not good enough," said lead researcher Richard Harrigan. "It's very risky to pick up your drugs and take them inconsistently. The good news is that although they require a very high level of adherence, these therapies do work." Baseline viral levels also were shown to be a predictor of the eventual development of drug resistance, according to the study. Study subjects with high viral loads when initiating anti-HIV drug therapy were 59% more likely to develop drug resistance than those who had low viral loads before beginning therapy.