Early versus delayed treatment with glatiramer acetate: Analysis of up to 27 years of continuous follow-up in a US open-label extension study.

Background: Glatiramer acetate (GA) is US-approved for relapsing multiple sclerosis.

Objectives: To describe GA long-term clinical profile. To compare effectiveness of early start (ES) versus delayed start (DS; up to 3 years) with GA.

Methods: Phase 3 trial participants entered a randomized placebo-controlled period then an open-label extension (OLE) with GA.

Results: Overall, 208 out of 251 (82.9%) randomized participants entered the OLE; 24 out of 101 (23.8%, ES) and 28 out of 107 (26.2%, DS) participants completed the OLE. Median GA treatment was 9.8 (0.1-26.3) years. Annualized change in Expanded Disability Status Scale (EDSS) score was lower with ES versus DS ( = 0.0858: full study;  = 0.002; Year 5). Participants with improved/stable EDSS was consistently higher with ES versus DS: 40.3% versus 31.6% ( = 0.1590; full study); 70.8% versus 55.6% ( = 0.015; Year 5). ES prolonged time-to-6-month confirmed disease worsening (CDW) versus DS (9.8 vs 6.7 years), time-to-12-month CDW (18.9 vs 11.6 years), and significantly reduced time-to-second-6-month CDW ( = 0.0441). No new safety concerns arose.

Conclusion: GA long-term treatment maintained clinical benefit with a similar safety profile to phase 3 results; a key limitation was that only 25% of participants completed the OLE. Early initiation of GA had sustained benefits versus delayed treatment.