Shares of Regeneron Pharmaceuticals dropped nearly 6 percent on Friday after a U.S. federal judge blocked the company and its partner Sanofi from selling their cholesterol-lowering drug on grounds of patent infringement.
On Thursday, U.S. District Judge Sue Robinson in Delaware banned the marketing, selling or manufacturing of Regeneron's cholesterol-lowering drug, Praluent, in the U.S after drugmaker Amgen accused them of infringing on a patent it holds for its drug Repatha.
Robinson ordered that the ban not take effect for 30 days to give the two companies time to appeal.
A spokesperson for Regeneron told CNBC the company believes it did not infringe on any valid patents and looks forward to the appeal. On Thursday, the two companies said in a joint statement the facts and controlling law support their position.
"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," said Karen Linehan, executive vice president and general counsel, of Sanofi.
Sanofi said Praluent was the first drug approved for use in the U.S. that knocks out a harmful protein responsible for a harmful amount of LDL cholesterol in the blood. LDL, or "bad" cholesterol, can lead to plaque buildup in arteries and result in heart disease or stroke, according to the Centers for Disease Control and Prevention.
The decision also marks a win for Amgen, and could boost the company's drug if the judge's ruling holds. Amgen shares gained about 2.5 percent Friday, while shares of Sanofi were down nearly 3 percent.
With Friday's declines, Regeneron's stock has declined 7 percent in the last 3 months.
—Reuters contributed to this report.