A study by Canadian researchers published in the December 1 edition of the journal Clinical Infection Diseases reports that there has been a significant decrease in the rates of resistance to HIV-1 drugs among patients treated for the disease.

Researchers attribute the drop in drug resistance to the successful use of Highly Active Antiretroviral Therapy (HAART), which is considered to be the combination of at least three antiretroviral drugs to maximally suppress HIV infection.

This study is of particular interest because to date there have been few studies evaluating changes in the rate of drug resistance among large numbers of treated individuals. Drug resistance has been one of the major barriers to sustained antiretroviral therapy.

Research indicates that barrier is coming down.

“Today, it is relatively rare for us to detect resistance that can compromise therapy, due to the availability of a wider variety of more active drugs and the use of highly active triple-combination regimens,” noted Dr. P. Richard Harrigan, director of Research Labs at the Centre for Excellence in HIV/AIDS, and one of the lead authors of the study.

Data was assembled using a total of 24,652 resistance tests from 5,422 patients receiving antiretroviral therapy from the British Columbia Drug Treatment Program between July 1996 and December 2008.

During this period of study, researchers found that the rate of patients developing new HIV-1 drug resistance fell 12-fold.

Plasma viral load, which is the amount of HIV virus present in the bloodstream, and drug resistance data were used by researchers as an indication of the HIV drug resistance rate.

Due to the high replication rate of HIV and its persistent ability to develop resistance against the current class of retroviral drugs, developing a long-lasting HIV therapy is difficult.

This study demonstrates the success of current treatments in preventing HIV-1 drug resistance among patients, although Dr. Harrigan cautions that more research can be done.

“Further studies should be carried out to look at the levels of emerging resistance among different treatment populations, including those receiving treatment in resource-limited settings,” he said. “Also, it will be important to monitor emergent resistance to newer drugs as they become more widely used.”

For more information about the study, please see the Clinical Infectious Diseases Web site.