The prevalence of injection-site reactions with disease-modifying therapies and their effect on adherence in patients with multiple sclerosis: an observational study

Background: Interferon beta (IFN beta) and glatiramer acetate (GA) are administered by subcutaneous (SC) or intramuscular (IM) injection. Patients with multiple sclerosis (MS) often report injection-site reactions (ISRs) as a reason for noncompliance or switching therapies. The aim of this study was to compare the proportion of patients on different formulations of IFN beta or GA who experienced ISRs and who switched or discontinued therapy because of ISRs. Methods: The Swiss MS Skin Project was an observational multicenter study. Patients with MS or clinically isolated syndrome who were on the same therapy for at least 2 years were enrolled. A skin examination was conducted at the first study visit and 1 year later. Results: The 412 patients enrolled were on 1 of 4 disease-modifying therapies for at least 2 years: IM IFN beta-1a (n = 82), SC IFN beta-1b (n = 123), SC IFN beta-1a (n = 184), or SC GA (n = 23). At first evaluation, ISRs were reported by fewer patients on IM IFN beta-1a (13.4%) than on SC IFN beta-1b (57.7%; P < 0.0001), SC IFN beta-1a (67.9%; P < 0.0001), or SC GA (30.4%; P = not significant [NS]). No patient on IM IFN beta-1a missed a dose in the previous 4 weeks because of ISRs, compared with 5.7% of patients on SC IFN beta-1b (P = 0.044), 7.1% of patients on SC IFN beta-1a (P = 0.011), and 4.3% of patients on SC GA (P = NS). Primary reasons for discontinuing or switching therapy were ISRs or lack of efficacy. Similar patterns were observed at 1 year. Conclusions: Patients on IM IFN beta-1a had fewer ISRs and were less likely to switch therapies than patients on other therapies. This study may have implications in selecting initial therapy or, for patients considering switching or discontinuing therapy because of ISRs, selecting an alternative option.