Rilonacept is a fusion protein designed to attach to and neutralize circulating IL-1 before it can attach to cell-surface receptors and generate signals that can trigger inflammation.

In September 2008, Regeneron announced the results of a Phase 2 study which evaluated the efficacy and safety of rilonacept in preventing gout flares induced by the initiation of urate-lowering drug therapy, which is commonly used to control gout. Regeneron is now enrolling patients in a Phase 3 rilonacept gout program which includes two studies in the prevention of gout flares in patients initiating urate-lowering therapy, one Phase 3 study evaluating rilonacept in the treatment of acute gout flares, and a separate safety study.

Gout is characterized by the deposition of uric acid crystals, a bodily waste product normally excreted by the kidneys, in the joints of the toes, ankles, knees, wrists, fingers, and elbows. These uric acid crystals can stimulate the release of inflammatory mediators, including interleukin-1 (IL-1), which result in acute flares of joint pain and inflammation. Patients with occasional gout attacks have a limited number of treatment options available that may not offer adequate pain relief or may not always be tolerated. There are 1.4 million patients treated for acute gout attacks each year in the U.S.

In patients with frequent gout attacks who have elevated blood levels of uric acid, chronic treatment with uric acid-lowering medicines, such as allopurinol, may be prescribed to eliminate the uric acid crystals and prevent reformation. During the first months of urate-lowering drug therapy, while uric acid blood levels are being reduced, the break up of the uric acid crystals, previously deposited in joints, can result in release of IL-1, causing acute flares of joint pain and inflammation. Anti-inflammatory therapy is sometimes used to help prevent these flares. However, the tolerability of these therapies can limit patients' adherence. Approximately 750,000 gout patients initiate urate-lowering drug therapy in the U.S. each year.

This section discusses Regeneron's pipeline of drug candidates currently undergoing clinical testing in a variety of diseases. These drug candidates have not been approved by the United States Food and Drug Administration for the indications described in this section.