How many injections did you miss last month? A simple question to predict interferon β-1a adherence in multiple sclerosis

Objectives: Adherence to treatment is of utmost importance in multiple sclerosis (MS) to achieve full benefits from disease-modifying treatments. Thus, we investigated predictors of adherence to interferon beta-1a. Methods: 114 relapsing-remitting MS subjects were recruited and followed-up during 1.536 +/- 0.961 years. RebiSmart (R) (Ares Trading SA, Coinsins, Switzerland), an electronic auto-injector, allows real-time recording of adherence which was retrospectively evaluated, and subjects were categorized accordingly: fully adherent (if no doses were missed), early or late missing (if missing the first dose during the first month of observation or later). The occurrence of clinical relapses and the annualized relapse rate (ARR) were prospectively recorded. Results: Adherence was 95.0 +/- 9.0%. Early missing (n = 17, 14.9%) was more likely to be associated with the occurrence of a clinical relapse (OR = 4.155; p = 0.018), but not late missing (n = 54, 47.4%) (OR = 1.454; p = 0.408), as compared to fully adherent (n = 43, 37.7%). Adherence was lower in early missing, as compared to late missing (p < 0.001). The ARR was higher in early missing, as compared to late missing and to fully adherent (p < 0.001). Conclusion: MS subjects missing an injection early presented lower adherence, and a fourfold chance of having a relapse, suggesting a simple way to assess and categorize adherence in a clinical, real-life setting, where lack of time often prevents more thorough evaluations.