Long-term subcutaneous interferon beta-1a therapy in patients with relapsing-remitting MS

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Abstract
Objective: To conduct systematic long-term follow-up (LTFU) of patients in the Prevention of Relapses and Disability by Interferon beta-1a Subcutaneously in Multiple Sclerosis (PRISMS) study to provide up to 8 years of safety, clinical and MRI outcomes on subcutaneous (SC) interferon (IFN) β-1a in relapsing-remitting multiple sclerosis (RRMS). Methods: The original cohort of 560 patients was randomized to IFNβ-1a, 44 or 22 μg three times weekly (TIW) or to placebo; after 2 years, patients on placebo were rerandomized to active treatment and the blinded study continued for a further 4 years. The LTFU visit was scheduled 7 to 8 years after baseline. Results: LTFU was attended by 68.2% of the original PRISMS study cohort (382/560 patients). 72.0% (275/382) were still receiving IFNβ-1a SC TIW. Patients originally randomized to IFNβ-1a 44 μg SC TIW showed lower Expanded Disability Status Scale progression, relapse rate and T2 burden of disease up to 8 years compared with those in the late treatment group. Brain parenchymal volume did not show differences by treatment group. Overall, 19.7% of patients progressed to secondary progressive MS between baseline and LTFU (75/381). No new safety concerns were identified and treatment was generally well tolerated. Conclusions: Despite the limitations inherent in any long-term study (for example, potential differences between returning and nonreturning patients), these results indicate that patients with relapsing-remitting multiple sclerosis can experience sustained benefit over many years from early interferon β-1a subcutaneous therapy three times weekly compared with patients whose treatment is delayed. This effect was more apparent in the patients receiving the higher dose.