Is the PCSK9 patent fight giving Amgen's Repatha a boost? Script numbers say so

As Sanofi and Regeneron scramble to keep their PCSK9 cholesterol drug Praluent on the market, Amgen’s rival drug Repatha already appears to be chipping away at its market share.

For the week of January 20, Repatha’s prescription total hit 3,231, ahead of Praluent’s 2,859, Bernstein analyst Ronny Gal reported in a Monday note. The 53%-to-47% ratio is the largest weekly gap since the middle of last year, the analyst wrote.

The Praluent partners are of course embroiled in a patent fight against Amgen, which claims that Sanofi and Regeneron knowingly stepped on its patents in developing Praluent. A district court jury sided with Amgen, and the judge in the case granted Amgen’s request for an injunction that would push Praluent off the market.

That threat has depressed Praluent scripts, Gal figures. “This should not be surprising,” he wrote. “As payers (and sometimes physicians) begin to consider the risk of Praluent removal from the market, they not surprisingly begin to prefer the safer option.”

Sanofi and Regeneron hope that the threat is short-lived; they’re trying to persuade the U.S. Circuit Court of Appeals in Washington, D.C., to put off the injunction while their patent appeal is heard. In their request for a stay, the two companies argued that they have a good chance of winning their appeal and that pulling Praluent in the meantime would do great damage to Regeneron. (If the trend on weekly script numbers continues, that's some obvious evidence of the latter claim.)

And then there’s the societal benefit of keeping both drugs, which Judge Sue Robinson herself mentioned in her order granting the injunction.

At least one patent expert believes that the two companies will succeed, which would allow Praluent to stay on the market. In a note to investors, Mizuho Securities said its intellectual property expert “believes that an oral hearing is likely to occur in the [first half of 2017] in the Federal Circuit with a decision before year-end 2017.”

Gal said he found Regeneron’s arguments persuasive. “From experience we learned never to try calling court decisions before seeing both sides, but we have to say the Regeneron arguments resonated with us,” he wrote in the Monday note. Amgen’s response is expected shortly.