Safety and clinical effectiveness of peginterferon beta-1a for relapsing multiple sclerosis in the real-world setting: Interim results from the Plegridy Observational Program

Background: The Plegridy Observational Program (POP) is an ongoing, 5-year, phase 4 real-world study of the safety and effectiveness of subcutaneous peginterferon beta-1a in patients with relapsing multiple sclerosis (RMS).& nbsp;Methods: This interim analysis from POP assessed the safety and effectiveness of peginterferon beta-1a, including subgroup analyses of patients aged < 50 and >=& nbsp;50 years, newly diagnosed and non-newly diagnosed patients, and new and experienced peginterferon beta-1a users.& nbsp;Results: A total of 1208 patients enrolled in POP. Mean (standard deviation) peginterferon treatment duration in the overall population was 757.0 (529.5) days. The overall incidence of treatment-emergent adverse events (AEs) was 65.5%, and the incidence was higher in new than experienced peginterferon beta-1a users (78.1 vs 52.4%). The overall incidence of treatment-emergent serious AEs was 7.6%, and the incidence was lower in younger than older patients (5.8 vs 11.1%). No new or unexpected safety signals were reported. Overall treatment discontinuation due to AEs occurred in 20.7% of patients, with a higher proportion of new than experienced peginterferon beta-1a users (27.0 vs 14.2%) discontinuing treatment due to AEs. Flu-like symptoms and injection site reactions were significant predictors of time to treatment discontinuation. The adjusted annualized relapse rate (ARR) was 0.12 (95% confidence interval 0.11-0.13) in the overall population and was similar across all subgroups. In the overall population at 4 years, 79.1% of patients were relapse free, the estimated cumulative proportion of patients with confirmed disability worsening was 1.8%, and > 67% of patients achieved clinical no evidence of disease activity (NEDA).& nbsp;Conclusions: Safety data of patients enrolled in POP are consistent with the established clinical safety profile of peginterferon beta-1a. In addition, the low ARR and high proportion of patients achieving clinical NEDA at 4 years across all subgroups indicates the effectiveness of peginterferon beta-1a in treating RMS in real-world clinical settings.