A comparison study of multiple measures of adherence to HIV protease inhibitors

Background: Poor adherence to HIV protease inhibitors may compromise the ef fectiveness of treatment. Few studies have compared methods for measuring a dherence or have related adherence measures to a clinical outcome. Objective: To examine the relationship among a composite score of adherence , the three primary measures of adherence, and HIV virologic response. Design: Longitudinal cohort study. Setting: Public HIV clinic. Patients: 108 HIV-infected adults receiving protease inhibitors or non-nucl eoside reverse transcriptase inhibitors who were monitored for 666 monthly intervals. Measurements: Medication Event Monitoring System (MEMS), pill count, and in terview combined into a composite adherence score (CAS), and HIV viral load . Results: Mean antiretroviral adherence differed by adherence measure (MEMS, 0.63; pill count, 0.83; interview, 0.93; and GAS, 0.76). Composite adheren ce score decreased significantly over time. Composite adherence score, MEMS values, pill values, and interview values were statistically significantly associated with achievement of an undetectable viral load within 6 months of initiating therapy. Composite adherence score showed the strongest predi ctive relationship (odds ratios for a 10% increase in adherence for GAS, ME MS, pill count and interview, respectively, were 1.26 [95% CI, 1.16 to 1.37 ], 1.13 [CI, 1.06 to 1.21], 1.10 [CI, 1.02 to 1.19], and 1.35 [CI, 0.93 to 1.94]). Conclusions: Different measures applied to the same patient suggest differe nt levels of adherence. Adherence may be underestimated by MEMS and overest imated by pill count and interview. A summary measure combining several mea sures is more strongly related to a clinical response, but more practical m easurement methods are needed for clinical use.