10. Remodulin

United Therapeutics was built by CEO Martine Rothblatt on Remodulin, which was approved in 2002.

10. Remodulin/Treprost
United Therapeutics/Mochida Pharmaceutical
2016 sales: $614 million

United Therapeutics was built on Remodulin. The company grew out of a career change for CEO Martine Rothblatt, who built Sirius satellite radio before getting into pharma. Her son’s diagnosis of pulmonary arterial hypertension (PAH) inspired the move—and Remodulin, which was approved in 2002.

Since then, several other companies have jumped into the PAH field. Actelion, whose drugs Opsumit and Tracleer are also on this list, drew a $30 billion buyout by Johnson & Johnson last year, putting its PAH portfolio in J&J’s hands. Gilead’s Letairis—also on this list—is a PAH treatment as well. And Bayer has its own competitor, Adempas, which it sees as one of its top growth products.

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Still, Remodulin is growing; its $602 million in 2016 sales were an uptick from $572.8 million in 2015. Another small part of $12 million came from Mochida Pharmaceutical, which sells the drug in Japan as Treprost.

Remodulin is nearing the end of its exclusivity, however; it’s set to face generic competition next year under patent settlements the company has struck with Teva Pharmaceutical and Sandoz. The company has won approval of a follow-up med, Orenitram, that it hopes can help fill the gap. It’s an oral version of Remodulin, so it comes in a more convenient form than its injectable predecessor. It brought in $130 million last year, an increase of almost one-third over 2015.

The company is also working on “multiple second-generation Remodulin delivery systems” that are now in late-stage testing, according to the company’s 2016 earnings release.

10. Remodulin