Background: Adherence to therapy with pegylated interferon and ribavirin for hepatitis C virus (HCV) infection has been incompletely examined.
Objective: To evaluate the relationship between adherence to HCV therapy and early and sustained virologic response, assess changes in adherence over time, and examine risk factors for nonadherence.
Design: Retrospective cohort study.
Setting: National Veterans Affairs Hepatitis C Clinical Case Registry.
Patients: 5706 HCV-infected patients (genotypes 1, 2, 3, or 4) with at least 1 prescription for both pegylated interferon and ribavirin between 2003 and 2006 and HCV RNA results before and after treatment initiation.
Measurements: Adherence was calculated over 12-week intervals by using pharmacy refill data. End points included early virologic response (decrease of ≥2 log(10) HCV RNA at 12 weeks) and sustained virologic response (undetectable HCV RNA 24 weeks after the end of treatment).
Results: Early virologic response increased with higher levels of adherence to ribavirin therapy over the initial 12 weeks (patients with HCV genotype 1 or 4, 25 of 68 [37%] with ≤40% adherence vs. 1367 of 2187 [63%] with 91% to 100% adherence [P < 0.001]; patients with HCV genotype 2 or 3, 12 of 18 [67%] with ≤40% adherence vs. 651 of 713 [91%] with 91% to 100% adherence [P < 0.001]). Among patients with HCV genotype 1 or 4, sustained response increased with higher adherence to ribavirin therapy over the second, third, and fourth 12-week intervals. Results were similar for adherence to interferon therapy. Mean adherence to therapy with interferon and ribavirin decreased by 3.4 and 6.6 percentage points per 12-week interval, respectively (P for trend < 0.001 for each drug). Patients who received growth factors or thyroid medications during treatment had higher mean adherence to antiviral therapy.
Limitation: This was an observational study without standardized timing for outcome measurements.
Conclusion: Early and sustained virologic responses increased with higher levels of adherence to interferon and ribavirin therapy. Adherence to therapy with both antivirals decreased over time, but more so for ribavirin.