Actemra works by blocking the effect of a certain protein associated with inflammation. But because Actemra acts to suppress the immune system, it can also have serious side effects, including severe infections, liver abnormalities and damage to digestive organs.
Rheumatoid arthritis affects about 1.3 million people in the U.S., according to the Arthritis Foundation.
The drug was co-developed with Japan's Chugai Pharmaceutical Co. and has been approved for use in Japan since 2005. It is also approved in the European Union, India, Brazil, Switzerland and Australia.