Changes in Antiviral Adherence over Time: Examining how antiviral adherence changes over the course of HCV therapy can identify time periods when antiviral adherence declines and when medical providers should emphasize the importance of adherence. In a cohort study among 5,706 patients with chronic HCV, mean adherence to pegylated interferon and ribavirin (determined by pharmacy refills over 12-week intervals) was high during the initial 12 weeks of treatment, but declined over the subsequent course of therapy (Figure 1). Overall, there was a mean decline in ribavirin adherence of 6.6 percentage points per 12-week interval and in interferon adherence of 3.4 percentage points per 12-week interval. Notably, during the final 12 weeks of HCV therapy for genotype 1 or 4 patients (i.e., weeks 36 to 48), mean adherence to pegylated interferon was 89% and mean adherence to ribavirin was 76%. Similar results were observed in a separate cohort study of HCV treatment adherence among 333 HIV/HCV-coinfected patients. In that study, there was a mean decline in interferon adherence of 2.5 percentage points and in ribavirin adherence of 4.1 percentage points per 12-week interval. Thus, these data indicate that adherence to both pegylated interferon and ribavirin declines during treatment, particularly after week 12 of therapy.
Within-Person Differences in Adherence to Interferon and Ribavirin: In both of the above studies, adherence to ribavirin was lower than adherence to pegylated interferon over each 12-week interval of HCV therapy. The authors suggested that the higher frequency of ribavirin administration (twice daily) may make it more burdensome to remember and more vulnerable to drop-offs in adherence over time. The authors also suggested that patients may select a day of the week on which they administer their pegylated interferon injection prior to the start of therapy, and this scheduling routine might facilitate higher levels of adherence for interferon than ribavirin.