Results of sustained long-term use of interferon beta-1a in a community-based cohort of patients with relapsing multiple sclerosis

BACKGROUND Few studies have evaluated long-term efficacy of interferon beta-1a in large community-based cohorts. OBJECTIVE Evaluate time to relapse, relapse rate, and disability progression in patients treated with intramuscular interferon beta-1a. METHODS A retrospective review of medical records from 2000-2010 was performed. Adult patients with relapsing-remitting MS or clinically isolated syndrome treated with interferon beta-1a were included. Primary outcomes were time to relapse, annualized relapse rate, and changes in Expanded Disability Status Scale score. Other outcomes included factors associated with time to first relapse, risk of having a relapse while receiving interferon beta-1a, and discontinuation of therapy. RESULTS In total, 364 of 696 patients screened were enrolled, with a mean age of 51 ± 12.1 years, disease duration of 9.39 ± 7.02 years, and duration of therapy of 4.03 ± 2.56 years. Mean time to first on-therapy relapse was 5.58 ± 0.26 years, annualized relapse rate was 0.30 ± 0.55 years, and mean increase in sustained Expanded Disability Status Scale score was 0.018. Relapse risk was associated with higher baseline Expanded Disability Status Scale score, age at disease onset, and number of relapses in the 12 months prior to therapy initiation. CONCLUSIONS This study demonstrates favorable clinical outcomes observed in a large community-based cohort, and serves to emphasize the continued therapeutic importance of interferon beta-1a, despite the development of newer agents with greater convenience of use, but also more potential risk of serious morbidity.