Drug resistance factors into HIV treatment failures.(Practice Trends)

BETHESDA, MD. -- Drug resistance poses a problem in treating HIV patients, in part because of the virus's high mutation rate, Roy M. Gulick, M.D., said at an annual conference on antimicrobial resistance sponsored by the National Foundation for Infectious Diseases.

Factors affecting HIV drug resistance include the virus itself, the antiretroviral drugs used, and the characteristics of the individual patient. Drug resistance is one of the main reasons why HIV treatments fail, said Dr. Gulick, director of the Cornell HIV Clinical Trials Unit at Weill Medical College of Cornell University, New York.

The goal of antiretroviral therapy (ART) is to suppress the viral load to as low a level as possible for as long as possible, he noted. Due to the high rate of mutation in the HIV virus, viral diversity is extensive. Failure to suppress viral load levels in the presence of antiretroviral drugs leads to the development of a resistant strain, Dr. Gulick explained.

Patient-related factors that can contribute to the development of resistance include the stage of disease, use of other medications, medication adherence, and side effects.

"We used to follow resistance clinically. If someone was taking their drugs, and their viral load went down, but then rose again, if we were sure that they were taking the medication, we assumed that they had developed resistance," he said. Today, genotypic tests provide viral sequencing of a patient's viral strain, and phenotypic tests can grow the patient's virus in vitro and assess resistance in the presence of the available antiretroviral drugs.

Are resistance tests clinically valuable? Dr. Gulick cited three studies, including one published in the Lancet, in which several hundred patients who had failed drug therapies were randomized to either ...