BOSTON (Reuters) - Sanofi SA and Regeneron Pharmaceuticals Inc have filed a lawsuit seeking a court order declaring that their eczema drug Dupixent, awaiting a U.S. approval decision, does not infringe an Amgen Inc patent for a failed asthma treatment.

Slideshow ( 2 images )

The lawsuit, filed in federal court in Boston on Monday, was intended to preempt one expected to be brought by Amgen, which has previously sued Sanofi and Regeneron over their rival cholesterol drug Praluent.

“Sanofi and Regeneron wish to eliminate any potential obstacle Amgen might seek to raise against the planned U.S. commercialization of Dupixent,” the plaintiffs said in the lawsuit.

Amgen said in a statement on Tuesday that the company “does have a patent covering the product and we will defend our patent rights.”

The suit came two months after a federal judge in Delaware blocked Sanofi and Regeneron from selling Praluent because it was found to infringe Amgen’s Repatha patent. Praluent was allowed to remain on the market during the appeals process.

Sanofi and Regeneron argue they have spent hundreds of millions of dollars developing Dupixent.

The injectable drug, known chemically as dupilumab, is seen as a critically important future growth driver for both companies, with annual sales forecast to exceed $5 billion by 2023, according to Thomson Reuters data.

The companies have called Dupixent a “game-changer” in moderate-to-severe atopic dermatitis, a type of eczema that causes extreme itching. The lawsuit said plans were under way to begin selling Dupixent as soon as it wins approval from the U.S. Food and Drug Administration, a decision due next week.

The patent at issue in the lawsuit was issued to Amgen in the 2000s, when it was attempting to develop an asthma treatment. Amgen abandoned development of the drug following disappointing results, the lawsuit said.

The complaint said that in recent days lawyers for Sanofi and Regeneron learned Amgen had hired lawyers to pursue patent infringement litigation related to Amgen’s work on that treatment. Dupilumab is also being tested for asthma and other indications.

“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 said in a statement on Tuesday.

The case is Sanofi-Aventis U.S. LLC et al v. Amgen Inc et al, U.S. District Court, District of Massachusetts, No. 17-cv-10465.