The stage is set for another big legal fight between archrivals Amgen Inc. (AMGN) and drug-development partners Regeneron Pharmaceuticals Inc. (REGN) and Sanofi SA (SNY).

Following the long-running legal patent battle for their cholesterol-fighting drugs Repatha and Praluent, the competing drug makers are set to lock horns in another legal battle, this time around eczema drug Dupixent (dupilumab), developed by Regeneron and Sanofi. (For more, see Amgen Keeps Patent Vs Regeneron, Sanofi.)

The partner companies are anticipating possible approval for Dupixent as early as next week. However, Amgen seems to have an old patent awarded to it in 2000's, when it was attempting to develop a treatment for asthma. While Amgen’s attempt on asthma therapy failed and the drug development was abandoned, the Thousand Oaks, California-based biotech continues to hold the key patent.

Sanofi and Regeneron believe that their eczema drug Dupixent may face a potential patent dispute from Amgen, as Dupixent is also being tested for asthma and other indications.

To avoid any disruptions to the possible marketing of the key drug once it secures approval, Regeneron and Sanofi have filed a preempt lawsuit to seek a court order declaration that their eczema drug Dupixent does not infringe a patent held by Amgen.

"We took this proactive step to protect the value of our innovative therapy Dupixent and ensure access of this important medicine for physicians and patients," Sanofi stated.

However, it appears that the battle lines are already drawn, as Amgen issued a statement saying that the company "does have a patent covering the product and we will defend our patent rights," reports Reuters.

In a similar patent infringement battle between the rival companies over their cholesterol lowering drugs, Amgen won the patent battle for its Repatha drug, but and Regeneron and Sanofi were allowed to keep their Praluent drug in the market leading to loss of market share for Amgen. (For more, see Amgen Rival Allowed to Keep Drug on Market.)

Dupixent is projected to hit peak sales exceeding $5 billion by the year 2023, and a successful launch will serve as a game changer for the partner companies. (See also, Regeneron Eczema Drug to Be Reviewed in EU.)

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