Assessing the validity of self-reported medication adherence in hepatitis C treatment

OBJECTIVE: To assess the validity of self-reported medication adherence provided by individuals in treatment for hepatitis C virus (HCV) infection with a regimen of peginterferon and ribavirin. METHODS: Adherence was evaluated prospectively among 196 African American and 205 white subjects enrolled in Virahep-C (Viral Resistance to Antiviral Thearpy of Chronic Hepatitis C), a treatment study for genotype 1 HCV infection. Adherence to the prescribed dose was measured by 2 methods: self-report questions administered during multiple clinic visits, using a touch screen computer; and recordings of bottle openings, using an electronic monitor placed inside the cap of prescription containers. Self-reported responses were compared with the electronic monitor data. Nonparametric tests were used to test the association between adherence measures at 4, 12, 24, 36, and 48 weeks of treatment. RESULTS: The estimated proportion of participants who were adherent prior to a given visit ranged from 85% to 97% (ribavirin) and 97% to 100% (peginterferon) by self report and from 69% to 90% (ribavirin) and 84% to 100% (peginterferon) by electronic monitors. For ribavirin, the percentage of cases in which the 2 measurement methods agreed varied from 68% to 90%; peginterferon agreement was from 84% to 100%. Overall, adherence was higher for peginterferon than for ribavirin but decreased over time for both medications. Self-reported adherence was usually higher than that assessed by electronic measures, and the level of descrepancy increased during the course of treatment. CONCLUTIONS: Adherence to peginterferon and ribavirin decreased gradually during therapy but remained relatively high. Simple self-reported measures can be used to screen for nonadherence to HCV drug therapy, but should be considered as overestimation of the actual amounts taken.