Evaluating the safety of beta-interferons in multiple sclerosis: A series of nested case-control studies

Objective: To examine the association between interferon-b (IFN-b) 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-b 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-b exposure for each potential adverse event with at least 30 cases. Cases were matched by age (65 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-b during follow-up. From the incidence analyses, 27 of the 47 potential adverse events had at least 30 cases. Patients with incident stroke (ORadj 1.83, 95% CI 1.16–2.89), migraine (ORadj 1.55, 95%CI 1.18–2.04), depression (ORadj 1.33, 95%CI 1.13–1.56), and hematologic abnormalities (ORadj 1.32, 95% CI 1.01–1.72) were more likely to have previous exposure to IFN-b than controls.
Conclusions: Among patients with RRMS, IFN-b 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.