People being treated for HIV are less likely now to develop drug-resistant infections, according to a British Columbia study on changes in drug therapy.

"Our results demonstrate that there has been a drastic decrease in the incidence of new cases of HIV-1 drug resistance," Dr. Richard Harrigan of the B.C. Centre for Excellence in HIV/AIDS and his colleagues concluded in a study reported in the journal Clinical Infectious Diseases.

The researchers attributed the success to new highly active antiretroviral therapy, known as HAART — usually a combination of three anti-retroviral drugs that are taken to suppress HIV infection. 

Before 1996, when people with HIV were prescribed just one or two HIV drugs, their infections were more likely to become drug-resistant and develop into full-blown AIDS.

The research involved 5,422 patients who received antiretroviral therapy from the British Columbia drug treatment program between July 1996 and December 2008. The researchers looked at more than 24,600 tests done on these patients over the years to determine whether their HIV had become resistant to drugs. 

They found that during this time, the rate of patients developing new drug resistance fell 12-fold. In one measure of the change, the researchers said that in 1996, the number of cases resistant to each class of antiretroviral drug was on average 571, but in 2008, it was 71.

Future resistance

With the HAART approach, viral levels are kept low so the disease doesn't worsen. Since the study was observational, it can't be known for certain, however, whether the drug regimen is responsible for the decline in resistance.

More research is needed in other populations, the authors said, but they were optimistic about the future.

"If current trends persist, the continued improvement of HAART and the increased availability of new drugs could potentially make the development of new HIV drug resistance a rare event," they wrote.

The research was funded by the Michael Smith Foundation for Health Research and the Canadian Institutes of Health Research.

Two of the study's authors reported receiving grants, advisory or speaking fees from several pharmaceutical companies.