9. Sensipar

Amgen is fighting to defend its blockbuster Sensipar against generics. (Amgen U.K.)

Company: Amgen
2017 U.S. sales: $1.347 billion
Use: Calcium reducer
Patent expiration: March 8

Amgen’s Sensipar is yet another example of the complicated process of anticipating generic launches. The drug's primary patent expired on March 8, but it also boasts a 2026 formulation patent that Amgen is using to try to defend its blockbuster.

Meanwhile, the drugmaker is in a legal battle with the FDA over pediatric exclusivity after the agency rejected Amgen's bid for six extra months of exclusive Sensipar protections. The company sued, arguing the FDA applied different standards to determining Sensipar's pediatric exclusivity bid than it did during a previous review for a Johnson & Johnson drug. Amgen's argument failed in district court in February, but the company is appealing.

Weeks later, when the drug's patent expired on March 8, the FDA approved copycats from Cipla and Aurobindo. 

When they'll hit the market is still in question, however. On the company’s fourth-quarter conference call, Amgen commercial head Tony Hooper said the drug’s outlook this year is “somewhat uncertain given the ongoing litigations.” 

“It is of course conceivable that competitors may be able to bring generic products to market at some point in 2018 although we believe we have strong litigation positions,” he added.

RELATED: Amgen sued FDA for a 6-month reprieve from Sensipar generics—and lost

Amgen has settled patent disputes with several generic players, according to Bernstein analyst Ronny Gal. The companies that have settled are likely to roll out their copies in the second half of 2018 through the end of 2019, Gal wrote in a March note. 

Generic companies that haven't settled "believe they can gain advantage over the other generics," Gal wrote, by launching sooner. They're confident they can win FDA approval and that their versions don't step on Amgen's formulation patent, he wrote; those launches could come in the second half of 2018, pending the result of the litigation.

The key word here is "could," and Amgen's 2018 outlook reflects that fact. Amgen execs partly attributed the billion-dollar range in the company’s 2018 guidance to the uncertainty about Sensipar sales. Analysts, for their part, are calling for a Sensipar revenue dropoff this year, with consensus estimates at $1.3 billion globally, down from $1.7 billion in 2017.

9. Sensipar