Association between beta-interferon exposure and hospital events in multiple sclerosis

Purpose: A systematic evaluation of hospital events can be an important surrogate measure for drug effectiveness or adverse effects. The purpose of this study was to examine the association between beta-interferon use and hospital events in a large cohort of patients with multiple sclerosis (MS). Methods: Retrospective cohort study comparing beta-interferon exposed and unexposed patients using clinical data from the British Columbia MS (BCMS) database linked with health administrative databases, 1996-2008. For each patient, the primary outcome was the number of hospital events in each month, analyzed by quasi Poisson regression. Beta-interferon exposure was examined two ways: current and cumulative exposure. Secondary outcomes included whether a hospital event occurred in each month for each specific primary diagnoses, grouped by International Classification of Diseases categories. Results: Current exposure to beta-interferon was not associated with an altered rate of hospital events (adjusted incident rate ratio 1.018; 95% CI 0.803-1.290). Similarly, there was no association with cumulative exposure. Cumulative beta-interferon exposure was associated with a lower odds of respiratory disease-related hospital events compared to those never exposed to beta-interferon. Conclusions: Exposure to beta-interferon for MS was not associated with a change in overall hospital event rates. Preliminary evidence suggests that the beta-interferons may have a protective effect against respiratory diseases requiring hospitalization in MS patients.