UPDATE 1-Abbott's Humira wins US ok for juvenile arthritis

(Adds details on Humira, rheumatoid arthritis)

NEW YORK, Feb 22 (Reuters) - Abbott Laboratories Inc (ABT.N) on Friday said U.S. regulators approved use of its blockbuster arthritis drug Humira to treat the new indication of juvenile rheumatoid arthritis.

Abbott said the U.S. Food and Drug Administration has approved use of the medicine, its best-selling product, to treat patients four years of age and older with moderate to severe rheumatoid arthritis. Patients will receive injections once every two weeks.

Rheumatoid arthritis is a condition in which inflammation causes joints -- usually including the hands and feet -- to become inflamed. The painful swelling often leads to destruction of joints.

Although the exact cause of the condition is not known, it is considered an autoimmune disease -- meaning one in which the immune system attacks the body's tissue.

Abbott estimated there are about 50,000 patients with juvenile arthritis in the United States, compared with about 1.3 million adults with the often-crippling condition.

Humira is also approved in Europe and the United States to treat Crohn's disease, a potentially dangerous inflammatory bowel ailment. The drug has annual global sales of more than $3 billion. (Reporting by Ransdell Pierson, editing by Gerald E. McCormick and Derek Caney)