ROCKVILLE, MD (FDA) -- FDA approved an application for etanercept (trade-name Enbrel), a genetically engineered protein, for a new indication for treatment of patients with active ankylosing spondylitis (AS), a chronic inflammatory disease affecting primarily the lower back and joints. The product is manufactured by Immunex Corporation, Thousand Oaks, Calif. and marketed by Amgen and Wyeth Pharmaceuticals. Etanercept is also licensed for treatment of patients with rheumatoid arthritis, juvenile rheumatoid arthritis, and psoriatic arthritis.

Approximately 350,000 patients in the United States have AS. The disease affects men more often than women. Symptoms of the disease may start in adolescence and are usually present by age 30. Patients often have lower back pain and stiffness, chest pain, joint pain and swelling, and tenderness due to the inflammation. In some patients the disease can cause significant pain and disability for many years.

Currently approved drugs for AS include some non-steroidal anti-inflammatory drugs (NSAIDS) which are approved to treat the symptoms of AS. Disease Modifying Anti-Rheumatic Drugs (DMARDS) that are approved for use in other inflammatory joint diseases are sometimes used when NSAIDS are ineffective, but none is FDA approved for use in the treatment of AS.

Etanercept binds to tumor necrosis factor (TNF), a naturally occurring protein in the body, and inhibits its action. TNF, which promotes inflammation in the body, is found at elevated levels in the blood and certain tissues of patients with AS. It is believed that interference with TNF plays a role in the beneficial effects of etanercept for AS. The major efficacy trial of etanercept for AS was a randomized, double-blind, placebo-controlled study of 277 patients. The study excluded patients with the most severe forms of AS. After six months of twice-weekly treatments, 58% of patients who received etanercept showed significant improvement on a scale that measured pain, function, and inflammation compared to 23% who received a placebo.

The main side effects of etanercept in the study were similar to those previously seen for this drug for other indications, including injection site reactions and upper respiratory infections. The approved labeling warns physicians about post-marketing reports of serious infections. The labeling says that Enbrel should not be given to patients with any active infection, including chronic or localized infections. It also recommends that patients who develop a new infection while being treated with Enbrel should be monitored closely.

Amgen will continue to follow patients in the trial to evaluate the long-term safety of etanercept in patients with AS.