Selective drug taking during combination antiretroviral therapy.

Objectives: Multidrug therapy is necessary to achieve sustained viral suppression. Discordant adherence to individual components of a multidrug regimen may lead to adverse outcomes. Methods: Antiretroviral-naive patients initiating therapy from 1997 through 2002 were included. Adherence for each antiretroviral was determined using pharmacy refill data. Selective drug taking was defined as ≥5% difference in adherence between 2 components of an antiretroviral regimen lasting at least 60 days. Results: A total of 322 of 415 patients (78%) met inclusion criteria. Selective drug taking occurred in 47 of 322 patients (15%) and on 51 of 438 regimens (12%). Factors associated with selective drug taking were lower baseline CD4 lymphocyte count (adjusted odds ratio [AOR]: 1.3, 95% CI: 1.1 to 1.6 per 100 cell/μL decrease); 3 times daily dosing schedule (AOR: 4.1, 95% CI: 1.1 to 15.5); and the presence of significant adverse drug events (AOR: 2.9, 95% CI: 1.3 to 6.4). Regimens containing a fixed-dose combination dosage form were less likely to have selective drug taking (AOR: 0.5, 95% CI: 0.2 to 0.99). Outcomes independently associated with selective drug taking included earlier progression to a new AIDS-defining illness or death (hazard ratio: 2.3, 95% CI: 1.2 to 4.5). Conclusions: Selective drug taking was relatively common among patients taking combination antiretroviral therapy. The factor most closely associated with selective drug taking was the presence of an adverse drug event. Clinical outcomes appeared worse in patients with selective drug taking.