Predictors of adherence and virologic outcome in HIV-infected patients treated with abacavir- or indinavir-based triple combination HAART also containing lamivudine/zidovudine

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Abstract
Objectives: To compare dosing convenience and adherence with abacavir (ABC) 300 mg plus a fixed-dose lamivudine 150 mg/zidovudine 300 mg combination tablet (COM) twice daily versus indinavir (IDV) plus COM twice daily in treatment-naïve, HIV-1-infected adults; and to evaluate the association among difficulty taking antiretroviral regimens, adherence, and virologic efficacy. Methods: An open-label, randomized, multicenter, international study compared the COM/ABC and IDV/COM regimens with respect to self-reported adherence and regimen convenience over 48 weeks. Logistic regression analysis (LRA) was done on a patient sub-sample from both groups to evaluate predictors of adherence and virologic response at last time-point on randomized therapy (LTORT). Results: The study population was diverse with respect to ethnicity (38% Asian, 27% Hispanic, 28% white, 3% black, 4% other) and gender (39% women, 61% men). Baseline median HIV-1 RNA was 4.80 log10 copies/mL and CD4+ cell count was 315 cells/mm3. Of 329 patients who were randomized and received treatment, 315 (96%) provided adherence data. Significantly more patients in the ABC/COM group than in the IDV/COM group reported ≥ 95% adherence to therapy (76 vs 58%, p < 0.001) and no difficulty in taking their regimen (91 vs 61%, p < 0.001). In both groups, the highest probability of HIV-1 RNA < 400 copies/mL occurred when median adherence was ≥ 95%. The probability of HIV-1 RNA < 400 copies/mL declined more rapidly in the IDV/COM group as adherence rates decreased. LRA showed that no difficulty taking any of the drugs in the regimen, ABC/COM treatment group, and male gender were independent significant predictors of ≥ 95% adherence ( p < 0.05). Median adherence and baseline HIV-1 RNA were significant predictors of HIV-1 RNA < 400 copies/mL ( p < 0.05). Conclusions: Patients reported greater ease of use and superior adherence to ABC/COM than IDV/COM. Patient-reported difficulty taking drugs in a regimen was predictive of reduced adherence, and both of the latter factors were predictive of poorer virologic outcome. Adherence levels of ≥ 95% in both treatment groups maximized the probability of patients achieving an HIV-1 RNA < 400 copies/mL.