Adherence to Nonnucleoside Reverse Transcriptase Inhibitor–Based HIV Therapy and Virologic Outcomes

BACKGROUND: Adherence of 95% or more to unboosted protease regimens is required for optimal virologic suppression in HIV-1-infected patients. Whether the same is true for nonnucleoside reverse transcriptase inhibitor (NNRTI)-based therapy is unclear. OBJECTIVE: To assess the relationship between adherence to NNRTI-based therapy and viral load in treatment-naive patients. DESIGN: Observational cohort study. SETTING: Private-sector HIV and AIDS disease management program in South Africa. PATIENTS: 2821 adults infected with HIV who began NNRTI-based therapy between January 1998 and March 2003 (2764 patients 98% were enrolled after December 2000). MEASUREMENTS: Adherence was assessed by monthly pharmacy claims. The primary end point was sustained viral load suppression (400 copies/mL). RESULTS: The median follow-up period was 2.2 years (interquartile range, 1.7 to 2.7 years). The proportion of patients with sustained viral load suppression ranged from 13% (41 of 325 patients) in patients who filled less than 50% of antiretroviral drug prescriptions to 73% (725 of 997 patients) in those who filled 100% of antiretroviral drug prescriptions. Each 10% increase in pharmacy claim adherence greater than 50% was associated with a mean absolute increase of 0.10 in the proportion of patients with sustained virologic suppression (P 0.20 x 10(9) cells/L), baseline viral load greater than 10(5) copies/mL (hazard ratio, 1.39 CI, 1.14 to 1.70), nevirapine-based regimen (hazard ratio, 1.43 CI, 1.16 to 1.75), and low pharmacy claim adherence (hazard ratio, 1.58 CI, 1.48 to 1.69, per 10% decrease in adherence to 50%). LIMITATIONS: Observational study with adherence stratification at study end and lack of standardized timing for outcome measurement. CONCLUSION: Virologic outcomes improve in a linear dose-response manner as adherence to NNRTI-based regimens increases beyond 50%.