Interferon ß-1a SC tiw Reduces Cumulative MRI Lesions over 24 Months in Patients with Relapsing Multiple Sclerosis: Post Hoc Analyses of PRISMS Data

Background: PRISMS was a multicenter, double-blind, placebo-controlled study in which 560 patients with relapsing multiple sclerosis were randomized to receive placebo or interferon beta-1a (IFN β-1a) given subcutaneously (SC) three times weekly (tiw) at doses of 44 µg or 22 µg over 2 years. A single-center cohort (n=39) had monthly magnetic resonance imaging (MRI) scans over the entire 24 months.

Objectives: To evaluate cumulative lesion activity up to specified time points (Months 1–9, 12, 18, and 24) in patients receiving placebo, IFN β-1a 44 μg SC tiw, or IFN β-1a 22 µg SC tiw and undergoing monthly MRI scans over 2 years.

Methods: Between-treatment differences in cumulative post-treatment active T2, gadolinium-enhancing (Gd+), and combined unique active (CUA) lesions (combination of active T2 and Gd+ lesions, avoiding double counting) were compared using negative binomial regression adjusting for the number of corresponding lesions at baseline.

Results: Mean CUA lesions were 2.5, 0.7, and 1.4 at baseline in the placebo (n=13) and IFN β-1a 44 μg (n=12) and 22 µg (n=14) SC tiw groups respectively; a cumulative mean of 19.7 CUA lesions was detected over 24 months post-baseline in the placebo group, versus 5.0 and 5.3 in the IFN β-1a 44 μg and 22 µg SC tiw groups, respectively. The cumulative number of CUA lesions was significantly (p<0.05) lower with IFN β-1a 44 µg SC tiw versus placebo by 2 months and at all subsequent time points evaluated (Months 3–9, 12, 18, and 24). Similar trends were seen for the cumulative mean number of active T2 (6.8, 1.5, and 1.8 for placebo, IFN β-1a 44 μg and 22 µg SC tiw groups) and Gd+ lesions (11.4, 2.2, and 3.4 respectively) over 24 months, although the differences between the IFN β-1a groups versus placebo were not significant. 

Conclusions: In this cohort of 39 patients undergoing monthly MRI scans for 24 months, a significant reduction in the cumulative mean number of CUA lesions with IFN β-1a 44 µg SC tiw versus placebo was seen as early as 2 months after the start of treatment and continued to be seen to Month 24.