Clinical and MRI efficacy of sc IFN β-1a tiw in patients with relapsing MS appearing to transition to secondary progressive MS: post hoc analyses of PRISMS and SPECTRIMS

This study evaluated efficacy of subcutaneous (sc) interferon beta-1a (IFN β-1a) 44 µg 3 × weekly (tiw) in patients appearing to transition from relapsing–remitting multiple sclerosis (RRMS) to secondary progressive MS (SPMS). The PRISMS study included 560 patients with RRMS (EDSS 0–5.0; ≥ 2 relapses in previous 2 years), and the SPECTRIMS study included 618 patients with SPMS (EDSS 3.0–6.5 and ≥ 1-point increase in previous 2 years [≥ 0.5 point if 6.0–6.5]) randomly assigned to sc IFN β-1a 44 or 22 µg or placebo for 2–3 years, respectively. These post hoc analyses examined five subgroups of MS patients with EDSS 4.0–6.0: PRISMS (n = 59), PRISMS/SPECTRIMS (n = 335), PRISMS/SPECTRIMS with baseline disease activity (n = 195; patients with either ≥ 1 relapse within 2 years before baseline or ≥ 1 gadolinium-enhancing lesion at baseline), PRISMS/SPECTRIMS without baseline disease activity (n = 140), and PRISMS/SPECTRIMS with disease activity during the study (n = 202). In the PRISMS and PRISMS/SPECTRIMS subgroups, sc IFN β-1a delayed disability progression, although no significant effect was observed in PRISMS/SPECTRIMS subgroups with activity at baseline or activity during the study (regardless of baseline activity). In the PRISMS/SPECTRIMS subgroup, over year 1 (0–1) and 2 (0–2), sc IFN β-1a 44 µg tiw significantly reduced annualized relapse rate (p ≤ 0.001), and relapse risk (p < 0.05) versus placebo. Similar results were seen for the PRISMS/SPECTRIMS with baseline disease activity subgroup. Subcutaneous IFN β-1a reduced T2 burden of disease and active T2 lesions in the PRISMS/SPECTRIMS subgroups overall, with and without baseline activity. In conclusion, these post hoc analyses indicate that effects of sc IFN β-1a 44 µg tiw on clinical/MRI endpoints are preserved in a patient subgroup appearing to transition between RRMS and SPMS.