A 8-year retrospective cohort study comparing Interferon-β formulations for relapsing-remitting multiple sclerosis

Background: Interferon-beta has been approved for the treatment of relapsing-remitting (RR) multiple sclerosis (MS), whereas its efficacy in preventing long-term disability and conversion to secondary progressive (SP) MS is still debated. We aim to compare long-term clinical evolution of newly-diagnosed RRMS patients treated with different Interferon-beta formulations. Methods: 507 patients were included in the analysis and followed-up for 8.5 +/- 3.9 years. 37.6% were treated with subcutaneous Interferon-beta 1a 44 mcg, 33.4% with intramuscular Interferon-beta 1a 30 mcg, and 29.0% with subcutaneous Interferon-beta 1b 250 mcg. Relapse occurrence, 1-point EDSS progression, reaching of EDSS 4.0 and conversion to SP were recorded as outcome measures. To reduce the selection bias, we calculated the propensity score of receiving the specific treatment considering age (32.7 +/- 8.3 years), gender (female 63.1%), disease duration (2.7 +/- 2.8 years), and baseline EDSS (1.5, range 1.0-3.5). Propensity score and covariates (age, gender, disease duration and EDSS) were included in the statistical models. Results: At Cox regression models, the reaching of EDSS 4.0 was not-significantly higher for Interferon-beta 1b 250 mcg (HR = 1.207; p = 0.063) and for Interferon-beta 1a 30 mcg (HR = 1.363; p = 0.095), when compared with Interferon-beta 1a 44 mcg. The rate of SP conversion was higher for Interferon-beta 1b 250 mcg (HR = 2.054; p = 0.042), and not-significantly higher for Interferon-beta 1a 30 mcg (HR = 1.884; p = 0.081), when compared with Interferon-beta 1a 44 mcg. Conclusions: Patients treated with Interferon-beta 1a 44 mcg presented with a marginally reduced risk of disability accrual in the long-term, when compared with Interferon-beta 1b 250 mcg and, at least in part, with Interferon-beta 1a 30 mcg. Formulation, frequency of administration and dose of Interferon-beta might affect the long-term clinical evolution of RRMS.