People taking an antiretroviral (ARV) treatment regimen that includes a protease inhibitor (PI) boosted with low-dose Norvir (ritonavir) were less likely to develop drug resistance than people taking other types of regimens, according to the authors of a study published in the July 1 issue of the Journal of Infectious Diseases.

Current federal HIV treatment guidelines recommend regimens containing either a Norvir-boosted PI or a non-nucleoside reverse transcriptase inhibitor (NNRTI) for people starting antiretroviral (ARV) treatment for the first time. If people can’t tolerate a boosted PI or an NNRTI, they may use a PI that isn’t boosted with low-dose Norvir.

To determine which regimens are likely to have the most prolonged benefit—and the least likely to be limited by the development of drug-resistance mutations in HIV—Viviane Lima, PhD, from the British Columbia Centre for Excellence in HIV/AIDS in Vancouver, and her colleagues compared the medical records of a cohort of 2,350 people living with HIV taking NNRTI-, boosted-PI-, or unboosted-PI-based regimens between August 1996 and November 2004.

Un-boosted PIs were most likely to be used in the late 1990s, with people often taking Crixivan (indinavir) or Viracept (nelfinavir). NNRTI use gained popularity around 1999, with many patients initially using Viramune (nevirapine). Boosted PI regimens gained favor beginning in 2002 and most commonly included Kaletra (lopinavir/ritonavir), followed by Reyataz (atazanavir).

Lima’s team found that the development of resistance occurred at the same rate in people who started treatment with an un-boosted PI as in those who started treatment with an NNRTI. However, people who started treatment with a boosted PI were nearly two and a half times less likely to develop drug resistance than people on an NNRTI or an un-boosted PI.

The year treatment was started also made a difference. Those starting treatment after 2002—regardless of the type of treatment regimen—were about 60 percent less likely to develop resistance than people who started treatment before 2002.