A simple, dynamic measure of antiretroviral therapy adherence predicts failure to maintain HIV-1 suppression

Background. High levels of antiretroviral therapy adherence are important for human immunodeficiency virus type 1 (HIV-1) suppression, yet the magnitude of adherence required to maintain it is less well characterized. Furthermore, methods to accommodate changes in adherence over time are lacking. In the present study, our objective was to determine the magnitude of antiretroviral therapy adherence needed to maintain HIV-1 suppression by use of a time-updated adherence measure that has the potential to be of use in a clinical setting. Methods. We examined a population-based cohort of HIV-1-infected subjects >= 18 years of age, residing in British Columbia, Canada, who started receiving antiretroviral therapy between 1 August 1996 and 30 September 2003, who had at least 2 consecutive viral loads < 500 copies/mL and who had prescriptions filled at least 3 times during a follow-up period ending 30 September 2004. Virological failure was defined as the second of 2 consecutive viral loads > 1000 copies/mL. Cox proportional hazards model was used to determine the relationship between virological failure and refill-based, time-updated surrogate measure of adherence. Results. Among the 1634 participants >= 18 years of age who initiated triple combination therapy during the study, 606 virological failure events were identified. In multivariate analyses, subjects with <= 95% adherence were 1.66 (95% confidence interval, 1.38-2.01) times more likely to experience virological failure than those with > 95% adherence. Conclusions. The highest levels of antiretroviral therapy adherence are associated with higher rates of maintained virological suppression. This simple, dynamic surrogate measure of adherence overcomes the limitation of single-point-in-time calculations of adherence and may be useful in real time to determine whether an individual is exhibiting incomplete adherence.