Objectives: To compare long-term adherence to antiretroviral therapy in an HIV service, as measured by self-report and by pharmacy records. To determine the level of adherence by each measure required to suppress viral load in a majority of patients.
Methods: The percentage of prescribed doses taken was calculated from (a) the number of missed doses in the previous 28 days reported by patients in a questionnaire at each clinic visit, and (b) pharmacy dispensing records. These were compared with each other and with HIV viral load data.
Results: Mean adherence was 96.2% by pharmacy record over 44 months and 98.6% by self-report over 25 months. The two methods correlated with each other (P<0.001) and the proportion of patients with viral load <400 HIV-1 RNA copies/mL increased with adherence as measured by self-report (P=0.001) and pharmacy record (P=0.004). Fewer than 60% of patients always had viral loads <400 copies/mL if adherence fell below 95% (pharmacy record) or 97% (self-report). Adherence was higher for once-daily than for twice-daily therapy (by pharmacy record: 97.2% vs. 96.0%; P<0.001). Adherence by both measures increased over time.
Conclusions: Self-reported antiretroviral adherence correlates with pharmacy dispensing records and predicts suppression of viral load at levels >or=97%. It is practical to adopt this into routine HIV clinical care.