Most people with HIV maintain good adherence to their antiretroviral (ARV) therapy during long periods, according to a study published online April 12 in AIDS. Maintaining high-adherence levels means that people could potentially keep their HIV suppressed for more than a decade without developing drug resistance.

As potent as combination ARV can be, it has an Achilles’ heal—the emergence of mutations that lead to drug resistance. This weakness, often triggered by fluctuations of ARV levels in the blood, demands that people remember to take almost all their doses on time, exactly as prescribed.

Researchers and HIV treatment experts have long feared that people living with HIV won’t be able to maintain high adherence levels over the long haul. Studies indicate that the concern is reasonable. Several have actually shown a drop in adherence over a two-year period.

These studies, however, have their share of weaknesses. They tend to be short, include only small numbers of people and rely on participants to self-report their adherence levels.

To determine adherence rates over many years, Valentina Cambiano and her colleagues from the University College London analyzed medical records and prescription refill records for 2,060 people enrolled in the Royal Free HIV Cohort study. The cohort includes HIV-positive people receiving care at the Royal Free Hospital in London.

The study participants were followed from the time of their first ARV prescription until the time of their last recorded ARV prescription or death. Most people started ARV treatment around 2000, with the earliest start date in 1998 and the last in 2003.

Contrary to expectation, adherence actually increased over time, even among those followed for up to 11 years. Among those followed for at least 11 years on ARV therapy, roughly 80 percent were still taking 95 percent or more of their doses correctly.  

Several groups were more likely to have poorer adherence. These included heterosexual black men and people with more than one previous treatment failure. Black women and people on Norvir (ritonavir)–boosted protease inhibitor regimens were more likely to maintain good adherence.

Cambiano’s group also looked at six-month periods during which a higher proportion of people had less than 95 percent adherence. These periods were most likely to occur between 1999 and 2002, which is not surprising given that regimens at that point included higher pill counts and had to be taken more often.

“In this analysis…we found no evidence of a decrease in average levels of adherence to [ARV therapy] over time, and even some evidence of a small increase,” the authors said. They concluding that the results offer “encouragement that maintenance of adherence for a lifetime may well be possible.”