People living with HIV are now able to remain on a first antiretroviral (ARV) regimen—which now usually includes once daily dosing and fewer pills—for much longer than people taking older twice-daily, multiple pill regimens, according to the authors of a study published in the October 1 issue of AIDS.

The majority of studies on first ARV regimen durability—the average length of time that a person's first ARV regimen continues to keep virus undetectable without needing to change medications for side effects or tolerability reasons—were conducted in the late 1990s using older medications that often needed to be taken two or more times per day and involved taking many pills. These studies suggested that people remained on these older ARV regimens without changes for efficacy, tolerability or safety, for about 1.6 years in real world settings. James Willig, MD, of the Infectious Diseases Unit at the University of Alabama in Birmingham (UAB), and his colleagues, however, reasoned that most ARV regimens are now much more convenient, tolerable and potent than older regimens and therefore likely have greater durability.

Dr. Willig's team studied the medical records of 542 patients enrolled in the UAB HIV clinic. They separated the patients into two groups, including 309 patients who'd started their first ARV regimen on or before July 31, 2004, and were more likely to be taken older combinations of drugs, and 233 who'd started ARV after July 2004, who were more likely to be taking newer combinations of drugs. The majority of the patients in both groups were male, and 56 percent were black. Nearly half had a history of mental illness, and many had a history of substance abuse.

Overall, Willig's team found that patients who started older regimens were significantly more likely to discontinue treatment due to side effects than people who started newer regimens. The duration of the first regimen was also nearly a year shorter, on average, in those on older regimens than newer regimens. In fact, the average length of time using a first regimen containing Videx (didanosine) or Zerit (stavudine) without switching for drug failure, side effects or tolerability was only 401 days, whereas the average regimen duration in those who started a regimen containing abacavir (found in Ziagen, Epzicom and Trizivir) or tenofovir (found in Viread, Truvada and Atripla) was 1,253 days.

When Willig's team conducted further analysis they found that once-daily dosing and the use of non-nucleoside reverse transcriptase inhibitors (NNRTIs) were the factors associated with the greatest duration. The authors recommend that further studies be conducted to determine whether these factors are consistently associated with better regimen duration.