Effect of adherence to newly initiated antiretroviral therapy on plasma viral load.

OBJECTIVE: To determine whether differences in adherence to newly initiated antiretroviral therapy exist between subjects who do and do not achieve undetectable plasma viral loads.
DESIGN: Observational cohort study monitoring adherence and virological and immunological parameters over the initial 4 months of therapy with nelfinavir. Adherence was measured using the microelectronic monitoring system (MEMS; APREX Corporation, Menlo Park, California, USA).
SETTING: General Clinical Research Center at a tertiary care center. PARTICIPANTS: Forty-one protease inhibitor-naive subjects with viral loads > 10 000 copies/ml newly starting a regimen including nelfinavir, referred from HIV clinics in Philadelphia. MAIN OUTCOME MEASURES: The primary outcome was undetectable viral load (< 50 copies/ml) after 4 months. Secondary measures included changes in viral load and CD4 cell counts. We hypothesized that adherence would be greater in subjects who achieved undetectable viral loads.
RESULTS: Adherence was greater in undetectable subjects, who took a median of 93% of prescribed doses [interquartile range (IQR) 84-96%], whereas detectable subjects took a median of 70% (IQR 46-93%). Adherence correlated with viral load decrease (Spearman's rho = 0.38, P < 0.01) and CD4 cell count increase (Spearman's rho = 0.25, P = 0.06). Despite differences between the groups over 4 months of therapy, there were no adherence differences over the first month [undetectables, 95% (IQR 88-98%) versus detectables, 94% (IQR 87-98%), P > 0.50].
CONCLUSIONS: Adherence is important in determining whether or not individuals achieve suppression with a newly initiated antiretroviral regimen. Adherence begins to wane after the first month of therapy. Therefore, closer assessment of adherence particularly after this first month is important.