Alemtuzumab (previously known as Campath(®)) is a humanized monoclonal antibody 
directed against the CD52 antigen on mature lymphocytes that results in 
lymphopenia and subsequent modification of the immune repertoire. Here we 
explore evidence for its efficacy and safety in relapsing-remitting multiple 
sclerosis. One Phase II and two Phase III trials of alemtuzumab versus active 
comparator (interferon beta-1a) have been reported. Two of these rater-blinded 
randomized studies assessed clinical and radiological outcomes in 
treatment-naïve patients; one explored patients who had relapsed despite 
first-line therapy. Compared to interferon beta-1a, alemtuzumab reduced the 
relapse rate by 49%-74% (P < 0.0001), and in two studies it reduced the risk of 
sustained disability accumulation by 42%-71% (P < 0.01). In one study 
(Comparison of Alemtuzumab and Rebif Efficacy in Multiple Sclerosis; CARE-MS1), 
there was no significant difference compared to interferon, perhaps reflecting 
the surprisingly low frequency of disability events in the comparator group. 
After alemtuzumab, the Expanded Disability Status Scale score improved by 
0.14-1.2 points, culminating in a net advantage with alemtuzumab of 0.41-0.77 
points over interferon in the CAMMS223 and CARE-MS2 trials (both P < 0.001). 
Radiological markers of new lesion formation and brain atrophy following 
alemtuzumab were significantly improved when compared to interferon in all 
studies. Adverse events were more common following alemtuzumab than interferon 
beta-1a (7.2-8.66 versus 4.9-5.7 events per person-year). While infusion 
reactions are the most common, autoimmunity is the most concerning; within Phase 
III studies, thyroid disorders (17%-18% versus 5%-6%) and immune 
thrombocytopenic purpura (1% versus 0%) were reported in patients taking 
alemtuzumab and interferon beta-1a, respectively. All patients responded to 
conventional therapy. One patient taking alemtuzumab in the Phase II study 
suffered a fatal intracranial hemorrhage following immune thrombocytopenic 
purpura, heralding assiduous monitoring of all patients thereafter. Alemtuzumab 
has been submitted for licensing in relapsing-remitting multiple sclerosis in 
the United States and Europe.