Background: In CARE-MS I (NCT00530348), 2 courses of alemtuzumab (baseline: 5 days; 12 months later: 3 days) improved outcomes vs SC IFNB-1a over 2 years in treatment-naive RRMS patients. Durable 6-year efficacy was demonstrated in an extension (NCT00930553) in absence of continuous treatment.

Objective: Evaluate alemtuzumab efficacy over 6 years in CARE-MS I patients who relapsed between Courses 1 and 2.

Methods: Assessments: annualised relapse rate (ARR); 6-month confirmed disability worsening (CDW); 6-month confirmed disability improvement (CDI); MRI disease activity (Gd+ and new/enlarging T2 lesions); new T1 hypointense lesions; brain volume loss (BVL).

Results: 15% of alemtuzumab-treated patients relapsed between Courses 1 and 2. Of these, 93% enrolled in extension; 87% remained through Year 6. ARR in Year 1 (1.3) declined in the year after Course 2 (0.3) and remained low over Years 3–6 (0.3–0.5). At Year 6, 60% were CDW-free, 24% achieved CDI, and most were free of Gd+ (84%) and new/enlarging T2 (71%) lesions, MRI disease activity (69%), and new T1 hypointense lesions (90%). Median percent yearly BVL declined (Years 1–6: –0.67%, –0.17%, –0.20%, –0.11%, –0.21%, –0.24%). After Course 2, 48% of patients received no additional treatment (alemtuzumab or other disease-modifying therapy).

Conclusions: Among 15% of patients who relapsed between alemtuzumab Courses 1 and 2, long-term outcomes were favourable, with nearly one-quarter achieving CDI. These data indicate that relapse after Course 1 is not indicative of subsequent limited treatment response and support administering alemtuzumab according to the approved 2 courses to achieve optimal clinical benefit.