Similar adherence rates favor different virologic outcomes for patients treated with nonnucleoside analogues or protease inhibitors

Background. This prospective study verified the effect of adherence on the risk of virologic failure. Methods. At enrollment in the study, a total of 543 patients who were following a steady ( duration, greater than or equal to 6 months) and effective ( viral load, ! 50 human immunodeficiency virus [ HIV] RNA copies/ mL) regimen of highly active antiretroviral therapy ( HAART) completed a self- reported questionnaire derived from the Adult AIDS Clinical Trials Group Adherence Follow- up Questionnaire. Patients were followed up for the subsequent 6 months to document virologic failure, which was defined as 2 consecutive viral load measurements of 1500 HIV RNA copies/ mL. Results. Only the type of treatment and the adherence rate at baseline were significantly associated with the virologic end point. Among patients who reported an adherence rate of less than or equal to 75%, the rate of virologic failure was 17.4%; this rate decreased to 12.2% for patients whose adherence rate was 76% - 85%, to 4.3% for patients whose adherence rate was 86% - 95%, and to 2.4% for patients whose adherence rate was >95%. When analysis was adjusted according to the type of regimen received, patients who were receiving protease inhibitor ( PI) - based HAART and who had an adherence rate of up to 85% had a virologic failure rate of 120%, whereas, only for patients who were receiving nonnucleoside reverse- transcriptase inhibitor ( NNRTI) - based HAART and who had an adherence rate of less than or equal to 75%, the virologic failure rate was 110%. For the comparison of NNRTI- treated patients and PI- treated patients with an adherence rate of 75% - 95%, the odds ratio was 0.157 ( 95% confidence interval, 0.029 - 0.852). The number of pills and daily doses received correlated with the reported adherence rate. Conclusions. Patients receiving NNRTIs report a higher rate of adherence than do patients receiving PIs. Adherence is significantly influenced by the number of pills and daily doses received. Low adherence is a major determinant of virologic failure; however, different therapies have different cutoff values for adherence that determine a significant increment of risk.