Content Validity and Reliability of a Self-Report Measure of Medication Nonadherence in Hepatitis C Treatment.

Nonadherence to direct-acting agents (DAAs) for hepatitis C (HCV) decreases viral response. To measure nonadherence to DAAs, a reliable, valid, and easily implemented method is needed. The goals of this study were to refine a previously validated (in patients with hypertension) self-report measure of extent of nonadherence and reasons for nonadherence in the context of DAAs and to obtain initial evidence of content validity and reliability. Phase I involved two focus groups with patients with HCV (n = 12) and one focus group with prescribers of HCV medications (n = 6) to establish content validity of reasons for nonadherence. Subsequent cognitive interviews with patients (n = 11) were conducted to refine items. Phase II was a prospective cohort study involving weekly administration of the refined measure by telephone to patients (n = 75) who are prescribed DAAs to evaluate reliability and consistency with viral response. In the cohort study, internal consistency ranged from acceptable (α = .69) to very high (α = 1.00) across time points and was quite high on average (α = .91). Across the 75 participants, there were 895 measurement occasions; of those, nonadherence was reported on only 27 occasions (3%), all of which occurred in the first 12 weeks. These 27 occasions represented 19 (26%) different individuals. At 12 weeks, 1 (1%) of patients had a detectable HCV viral load; at 12–24 weeks posttreatment, 4 (5%) had a sustained viral response. Nonadherent patients reported an average of 1.41 reasons for nonadherence. This multi-method study established content validity of reasons for nonadherence and reliability of extent of nonadherence. High rates of adherence and viral response were consistent with previous studies using other nonadherence measurement methods.