Goldman JD, Cantrell RA, Mulenga LB, Tambatamba BC, Reid SE, Levy JW, Limbada M, Taylor A, Saag MS, Vermund SH, Stringer JSA, Chi BH
We evaluated the association between two antiretroviral therapy (ART) adherence measurements—the medication possession ratio (MPR) and patient self-report—and detectable HIV viremia in the setting of rapid service scale-up in Lusaka, Zambia. Drug adherence and outcomes were assessed in a subset of patients suspected of treatment failure based on discordant clinical and immunologic responses to ART. A total of 913 patients were included in this analysis, with a median time of 744 days (Q1, Q3: 511, 919 days) from ART initiation to viral load (VL) measurement. On aggregate over the period of follow-up, 531 (58%) had optimal adherence (MPR ≥95%), 306 (34%) had suboptimal adherence (MPR 80–94%), and 76 (8%) had poor adherence (MPR <80%). Of the 913 patients, 238 (26%) had VL ≥400copies/ml when tested. When compared to individuals with optimal adherence, there was increasing risk for virologic failure in those with suboptimal adherence [adjusted relative risk (ARR): 1.3; 95% confidence interval (CI): 1.0, 1.6] and those with poor adherence (ARR: 1.7; 95% CI: 1.3, 2.4) based on MPR. During the antiretroviral treatment course, 676 patients (74%) reported no missed doses. The proportion of patients with virologic failure did not differ significantly among those reporting any missed dose from those reporting perfect adherence (26% vs. 26%, p=0.97). Among patients with suspected treatment failure, a lower MPR was associated with higher rates of detectable viremia. However, the suboptimal sensitivity and specificity of MPR limit its utility as a sole predictor of virologic failure.