Background & Aims: Patient adherence to prescribed antiviral therapy in human immunodeficiency virus infection enhances response. We evaluated the impact of adherence to combination therapy with interferon or peginterferon plus ribavirin in chronic hepatitis C patients. Methods: We assessed the effect of dose reduction on sustained virologic response (SVR) from prior trials with interferon α-2b plus ribavirin (n = 1010) or peginterferon α-2b 1.5 μg/kg/week plus ribavirin (n = 511). The actual treatment administered was verified from drug dispensing/return records and patient diaries. Two groups were defined: (1) patients who received ≥80% of both their total interferon and ribavirin doses for ≥80% of the expected duration of therapy and (2) patients who received reduced doses (<80% of one or both drugs for ≥80% of the expected duration of therapy). A statistical model provided comparative estimates of the response rates in compliant patients. Results: Most patients were at least 80% compliant with interferon α-2b/ribavirin or peginterferon α-2b/ribavirin therapy and had SVR rates of 52% and 63%, respectively, for the 2 regimens. This was most apparent for HCV-1-infected patients. The impacts of adherence on efficacy from subgroup analysis and the statistical modeling approach were similar. Conclusions: HCV-1-infected patients who can be maintained on >80% of their interferon or peginterferon α-2b and ribavirin dosage for the duration of treatment in the setting of a clinical trial exhibit enhanced sustained response rates. Our results suggest that adherence will enhance the likelihood of achieving an initial virologic response. Adherence beyond 12-24 weeks will be advantageous only for those patients who have achieved such an early virologic response.
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