Two trials, published in the Lancet medical journal, compared the effectiveness of alemtuzumab with a first-choice drug, interferon beta-1a.

BBC: Multiple sclerosis: New drug 'most effective'

He said he thought the drug would be most useful for patients for whom standard treatment had failed and in a "minority" of patients as a first-choice drug.

BBC: Multiple sclerosis: New drug 'most effective'