A US court has reversed an earlier decision banning the sale of Sanofi and Regeneron’s Praluent in the country and ordered a new trial.

The original trial was brought about because Amgen claimed Praluent, the first PCSK9 antibody to be approved for use in the US, infringed patents on its rival drug, Repatha.

In the decision, the Federal Circuit ruled that the trial court erred by excluding evidence regarding written description; excluding evidence on enablement; improperly instructing the jury on written description, holding that the law requires "a written description of the invention", meaning the claimed antibody itself and not the antigen; and improperly granting a permanent injunction.

The Federal Circuit also affirmed the trial court's ruling that Amgen's patents were non-obvious, which was one of Sanofi and Regeneron's several challenges to validity of Amgen's patents. Because of the improper exclusion of evidence, the court considered the record to be incomplete and concluded at this time that Sanofi and Regeneron are not entitled to judgment as a matter of law (JMOL) on the issues of written description and enablement.

The schedule for the new trial has not yet been determined. In a statement the companies said that they do not anticipate any new trial proceedings to start in 2017.

"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," said Karen Linehan, Executive Vice President and General Counsel, Sanofi. "It is our longstanding position that Amgen's asserted patent claims are invalid, and we remain confident in the long-term availability of Praluent for patients."

Meanwhile, Amgen said it was disappointed by the ruling. “We firmly believe in the validity of our patents and we look forward to reasserting our rights in court,” the company added in a statement.