The Mathilda and Terence Kennedy Institute of Rheumatology Trust filed its lawsuit in federal court in Delaware, seeking royalties and damages from Wyeth and Amgen for infringing a patent for treating arthritis. The drug makers jointly market Enbrel, a best-selling med, for treating rheumatoid arthritis.

In its lawsuit, the trust alleges its 2001 patent was developed by Marc Feldmann and Ravinder Maini, both with the Imperial College London. The patent relates to treating arthritis by co-administering methotrexate and drugs that block receptors to an inflammation-causing protein called tumor necrosis factor alpha (anti-TNFa) such as Enbrel, according to the lawsuit (you can read it here).

Amgen and Wyeth have refused demands for royalty payments, the complaint said. The Enbrel website says the drug can be used in combination with methotrexate. “Amgen believes we do not infringe or induce infringement of any valid enforceable claim of this patent,” Amgen spokesman David Polk tells Reuters. He described the trust’s claims as “meritless.”