Regeneron Pharmaceuticals Inc and Sanofi SA said on Thursday they would appeal the U.S. District Court ruling which banned the two companies from selling their cholesterol drug, Praluent (alirocumab), on grounds of patent infringement.
A federal judge had earlier blocked Sanofi and Regeneron from selling the drug after Amgen Inc accused them of infringing its patents.
U.S. District Judge Sue Robinson in Delaware had ordered that the ban not take effect for 30 days to give Sanofi and Regeneron time to appeal.
"It is our longstanding position that Amgen's patent claims are invalid and that the best interests of patients will be greatly disserved by an injunction preventing access to Praluent," Sanofi's Executive Vice President Karen Linehan said in a statement.
Amgen was up about 4 percent in after-hours trading, while Sanofi's U.S. shares were down 3.6 percent. Regeneron was down 1.1 percent before the company requested that trading be halted.
Amgen had sought the ban in an October 2014 lawsuit against Paris-based Sanofi and Tarrytown, New York-based Regeneron. It said Praluent, a PCSK9 inhibitor that lowers LDL cholesterol, infringed its patents related to the protein.
Thousand Oaks, California-based Amgen makes a rival drug called Repatha (evolocumab).
A jury found Amgen's patents valid in March. The defendants said after the verdict that they planned to appeal to the U.S. Federal Circuit Court of Appeals, which reviews patent disputes.
The companies could still decide to reach a settlement that would give Amgen royalties on Praluent sales.
The FDA approved Praluent and Repatha in 2015.
The drugs are more costly than other cholesterol drugs, with a list price topping $14,000 annually.
Sales of the expensive new drugs, seen as potential blockbusters, have been very slow to take off as health insurers and other payers have been reluctant to pay for them. Amgen reported just $40 million in Repatha sales in the third quarter.
Both drugs are in the final stages of enormous trials designed to demonstrate that they can lower the risk of heart attacks and deaths, which is expected to help open the insurer purse strings if successful. So-called outcomes results for Repatha are expected this quarter.
"If Praluent was gone from the market the long-term peak sales for Repatha could move from $2 billion to $3 billion to $4 billion worldwide, in theory," RBC Capital Markets analyst Michael Yee said in a research note. He added that without the outcomes results, the potential size of the market remained uncertain.