(Adds outside attorney, company, analyst comments, background; updates shares)
By Brendan Pierson
Oct 5 (Reuters) - A U.S. appeals court on Thursday threw out a ban on the sale of Regeneron Pharmaceuticals Inc and Sanofi SA's cholesterol-lowering drug Praluent, and ordered a new trial after finding a jury was given improper instructions.
The ruling from the U.S. Court of Appeals for the Federal Circuit in Washington was a setback for Amgen Inc, which claimed Praluent infringed patents on its rival drug, Repatha, and had won the sales ban after a jury trial.
Amgen, which brought its lawsuit in 2014, said in a statement it was disappointed by the court's action. "We firmly believe in the validity of our patents and we look forward to reasserting our rights in court."
Regeneron shares jumped 4.4 percent to $475.95 on the Nasdaq, while Sanofi shares in Paris rose 0.8 percent. Amgen shares were off 1.5 percent at $185.76 on the Nasdaq.
Praluent and Repatha are injectable biotech medicines created from manmade antibodies that dramatically lower levels of "bad" LDL cholesterol in the blood by blocking a protein called PCSK9.
Amgen claimed its patents covered a broad range of antibodies that bind to PCSK9, while Sanofi and Regeneron argued such broad patents were invalid.
In Thursday's decision, the Federal Circuit said jurors were given instructions that could have wrongly led them to believe that describing a protein like PCSK9 was enough to patent a broad class of possible antibodies.
The appeals court also found that the judge in the case improperly excluded some evidence that Regeneron and Sanofi wanted to use at the trial.
"We are pleased with the Federal Circuit's decision to remand for a new trial that allows us to present our complete evidence to the jury," Sanofi General Counsel Karen Linehan said.
In a joint statement, Regeneron and Sanofi said a new trial has not yet been scheduled and they do not expect proceedings to start this year.
Mizuho Securities analyst Salim Sayed said he expects the ruling will keep Praluent on the market for at least another year.
A jury had found Amgen's patents valid last March. Sanofi and Regeneron did not dispute that if the patents were valid, Praluent infringed them.
In January, U.S. District Judge Sue Robinson in Delaware took the unusual step of blocking sales of Praluent. She found that, although having both drugs on the market would be in the public interest, Amgen's patent rights outweighed that concern.
Praluent sales were allowed to continue during the appeals process.
Zachary Silbersher, a New York-based patent lawyer not connected with the case, said the court’s ruling will make it more difficult for Amgen to win if it goes to trial again, which could push the company to settle.
Praluent and Repatha won U.S. approval to reduce LDL cholesterol in 2015. The drugs are far more costly than other cholesterol drugs, with a list price topping $14,000 annually.
Hurdles to patient access by health insurers and pharmacy benefit managers have led to disappointingly low sales so far. But Amgen's drug has steadily gained market share since the court ruling, which threatened to remove Praluent from the market, rising to nearly 65 percent. (Reporting By Brendan Pierson in New York, additional reporting by Bill Berkrot in New York; editing by Bernadette Baum and Jonathan Oatis)