The Food and Drug Administration has approved Lemtrada, a treatment for relapsing multiple sclerosis made by the drugmaker Genzyme.

The drug has already been approved by the European Medicines Agency for use in the European Union and in Canada and Australia. Late last year, the FDA had said that the drug was not ready for approval in the U.S. market.

Sanofi, the parent company of Genzyme, wants to market Lemtrada as a treatment for relapsing multiple sclerosis, a disease in which the immune system attacks healthy nerves. It can cause pain, numbness, slurred speech, impaired vision, muscle weakness and neurological problems. Sanofi estimates that the disease affects more than 2.3 million people around the world and about 400,000 in the U.S.

The company said Saturday that Lemtrada "should generally be reserved for patients who have had an inadequate response to two or more drugs indicated for the treatment of MS." The drug's label will include a warning noting a risk of "serious, sometimes fatal autoimmune conditions, serious and life-threatening infusion reactions," Sanofi said.

Lemtrada's chemical name is alemtuzumab. It has also been approved for use as a leukemia treatment under the brand name Campath.

The French pharmaceutical company recently fired its CEO, Christopher Viehbacher, following a board room rift in which the chairman complained about his management style and an "inappropriate" lack of communication.