11. Letairis

Gilead's Letairis is losing patent protections this summer. (Image: Gilead China)

Company: Gilead
2017 U.S. sales: $887 million
Disease: Pulmonary arterial hypertension
Patent expiration: July 29

Just as Gilead expects another steep decline in hepatitis C sales this year, it's also anticipating the loss of patent protections for an important, if smaller, contributor: Letairis, a treatment for pulmonary arterial hypertension.

First approved in 2007, the drug brought in $887 million in U.S. sales last year. Its patent life runs out in July, Gilead CFO Robin Washington told analysts on the company’s fourth-quarter earnings call. In a year-end investor presentation, the drugmaker said it expects copycat competition to take a $300 million to $400 million bite out of Letairis sales this year.

That decline comes even as Gilead is forecasting $3.5 billion to $4 billion in hep C sales for 2018, far short of analyst expectations of $5 billion—and way down from peak levels in 2015 and 2016.

RELATED: Gilead's Biktarvy wins megablockbuster HIV nod, and rival GlaxoSmithKline strikes back

Gilead is hoping newer meds can help it absorb the Letairis hit and hep C declines, and one drug it's counting on for help is its new HIV launch Biktarvy. Approved in February, the med comes with megablockbuster expectations; peak sales estimates range from $6 billion to $10 billion.

And then there's Gilead's move into CAR-T. After inking its $11.9 billion Kite Pharma buyout last year, it won a second-to-market CAR-T approval for Yescarta in October, trailing Novartis’ Kymriah.

Gilead isn't the only company that stands to suffer from Letairis’ patent loss. Johnson & Johnson's Opsumit—acquired along with Actelion last year—could see sales eroded, too, J.P. Morgan analysts concluded in a research report. “[P]hysician preference data and more favorable coverage already give Letairis an edge” over the J&J drug, the analysts point out. And as history shows, when one drug in a particular field goes generic, other competitors often suffer.

Still, Gilead and J&J could get something of a reprieve. The J.P. Morgan analysts cautioned that Letairis generics could see REMS delays that have held up other copycats.

11. Letairis