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

ObjectiveTo determine whether differences in adherence to newly initiated antiretroviral therapy exist between subjects who do and do not achieve undetectable plasma viral loads. DesignObservational 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). SettingGeneral Clinical Research Center at a tertiary care center. ParticipantsForty-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 measuresThe 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. ResultsAdherence 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 ρ = 0.38, P < 0.01) and CD4 cell count increase (Spearman's ρ = 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]. ConclusionsAdherence 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.