Evaluating the safety of β-interferons in MS: A series of nested case-control studies

OBJECTIVE: To examine the association between interferon-β (IFN-β) and potential adverse events using population-based health administrative data in British Columbia, Canada. METHODS: Patients with relapsing-remitting multiple sclerosis (RRMS) who were registered at a British Columbia Multiple Sclerosis Clinic (1995–2004) were eligible for inclusion and were followed up until death, absence from British Columbia, exposure to a non–IFN-β disease-modifying drug, or December 31, 2008. Incidence rates were estimated for each potential adverse event (selected a priori and defined with ICD-9/10 diagnosis codes from physician and hospital claims). A nested case-control study was conducted to assess the odds of previous IFN-β exposure for each potential adverse event with at least 30 cases. Cases were matched by age (±5 years), sex, and year of cohort entry, with up to 20 randomly selected (by incidence density sampling) controls. Odds ratios (ORs) with 95% confidence intervals (95% CIs) were estimated with conditional logistic regression adjusted for age at cohort entry. RESULTS: Of the 2,485 eligible patients, 77.9% were women, and 1,031 were treated with IFN-β during follow-up. From the incidence analyses, 27 of the 47 potential adverse events had at least 30 cases. Patients with incident stroke (OR(adj) 1.83, 95% CI 1.16–2.89), migraine (OR(adj) 1.55, 95% CI 1.18–2.04), depression (OR(adj) 1.33, 95% CI 1.13–1.56), and hematologic abnormalities (OR(adj) 1.32, 95% CI 1.01–1.72) were more likely to have previous exposure to IFN-β than controls. CONCLUSIONS: Among patients with RRMS, IFN-β was associated with a 1.8- and 1.6-fold increase in the risk of stroke and migraine and 1.3-fold increases in depression and hematologic abnormalities.