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

BACKGROUND: Interferon-β 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-β 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-β1a 44mcg, 33.4% with intramuscular Interferon-β1a 30mcg, and 29.0% with subcutaneous Interferon-β1b 250mcg. 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-β1b 250mcg (HR = 1.207; p = 0.063) and for Interferon-β1a 30mcg (HR = 1.363; p = 0.095), when compared with Interferon-β1a 44mcg. The rate of SP conversion was higher for Interferon-β1b 250mcg (HR = 2.054; p = 0.042), and not-significantly higher for Interferon-β1a 30mcg (HR = 1.884; p = 0.081), when compared with Interferon-β1a 44mcg.

CONCLUSIONS: Patients treated with Interferon-β1a 44mcg presented with a marginally reduced risk of disability accrual in the long-term, when compared with Interferon-β1b 250mcg and, at least in part, with Interferon-β1a 30mcg. Formulation, frequency of administration and dose of Interferon-β might affect the long-term clinical evolution of RRMS.