OBJECTIVES: In the phase 3 CARE-MS II study (NCT00548405), alemtuzumab demonstrated a reduction in annualized relapse rate (49%) and sustained accumulation of disability (42%) versus subcutaneous interferon beta-1a 44 μg (both P<0.01). This analysis assessed the budget impact (BI) of adding alemtuzumab to a formulary containing approved disease-modifying therapies (DMTs) for multiple sclerosis (MS) in a hypothetical 100,000-member US health plan. METHODS: Alemtuzumab was administered as 2 annual treatment courses to patients with relapsing-remitting MS inadequately responding to prior therapy, with as-needed retreatment in an extension (NCT00930553). A