Eli Lilly has been defeated in a patent infringement lawsuit, brought by Ariad Pharmaceuticals, that could see it having to pay royalties on its Evista osteoporosis drug and Xigris for sepsis.

The jury in the case decided that a US patent held by Ariad (No 6,410,516) is valid and infringed by Evista (raloxifene) and Xigris (drotrecogin alfa), which contributed $1.04 billion and $215 million, respectively, to Lilly’s coffers in 2005. Ariad was awarded $65 million in back royalties in the case, and will be entitled to additional royalties on future sales of the two products out to 2019.

Lilly immediately said it would appeal the ruling. The patent in question was awarded in 2002 and covers the cell signaling activity of a nuclear factor called NF-(kappa)B, which Ariad claims is involved in the mechanism of action of a number of biologic drugs.

“The Ariad position is equivalent to discovering that gravity is the force that makes water run downhill and then demanding the owners of all the existing hydroelectric plants begin to pay patent royalties on their use of gravity,” said Lilly general counsel Robert Armitage. “We just don't believe that the patent law could possibly move in such a direction."

The patent is also the subject of a dispute between Ariad and US biotech giant Amgen. The latter filed a pre-emptive lawsuit aimed at invalidating the patent a few days ago, on concerns that Ariad might also seek royalties on sales of Amgen’s $2.5 billion rheumatoid arthritis drug Enbrel (etanercept), and another arthritis drug Kineret (anakinra).

Ariad was joined in the Lilly lawsuit by Harvard College, the Massachusetts Institute of Technology and the Whitehead Institute of Biomedical Technology, a nonprofit research institution.