Relationship between adherence level, type of the antiretroviral regimen, and plasma HIV type 1 RNA viral load: a prospective cohort study.

The relationship between adherence, antiretroviral regimen, and viral load (VL) suppression was assessed through a 1 year prospective follow-up study among 1142 HIV-infected patient. Patients on antiretroviral therapy who attended to the pharmacy during a 6-month period were considered eligible. Those included in the final analysis were patients who had been taking the same antiretroviral therapy for > or =6 months since their inclusion. The cohort included patients taking first line therapy (n = 243) and antiretroviral-experienced patients (n = 899). Naive patients who were included had to have reached undetectable VL at enrollment. Antiretroviral-experienced patients with detectable VL determinations in the previous 6 months were excluded. Adherence was measured by means of announced pill counts and dispensation pharmacy records. Of patients, 58% were taking NNRTI, 31.4% boosted PI, and 10.6% unboosted PI-based regimens. Overall, the relative risk of virologic failure was 9.0 (95% CI 4.0-20.1) in patients with adherence 80-89.9%, 45.6 (95% CI 19.9-104.5) with adherence 70-79.9%, and 77.3 (95% CI 34.2-174.9) with adherence <70%, compared with adherence of > or =90%. The risk of virologic failure in patients with adherence <90% taking unboosted PI was 2.5 times higher than the group taking boosted PI (95% CI 1.2-5.3). There were no statistical differences in patients taking boosted PI and those who were taking NNRTI. Less than 95% of adherence is associated with high virologic success. For patients taking NNRTI- or boosted PI-based regimens with adherence rates of 80%, the failure rate is <10%. These data do not affect the goal of achieving the highest level of adherence possible.