Bayer's now-approved Adempas girds for market-share battle in PAH

Bayer scored another R&D success with the FDA approval of Adempas (riociguat) for two rare pulmonary disorders. It's the first of a new generation of drugs for pulmonary arterial hypertension, and it's a pill rather than an injectable, which gives it a convenience advantage over some older meds. But with a rival drug candidate breathing down its neck, Bayer will have to carve out a place in that market quickly.

Adempas will initially compete with a few much older drugs, including Actelion's ($ATLN) Tracleer (bosentan), which brought in $1.6 billion last year, and Gilead Sciences' ($GILD) Letairis (ambrisentan), which brought in $410 million. United Therapeutics ($UTHR) sells Remodulin, another injectable. Then there's Pfizer's ($PFE) Revatio, which contains the same active ingredient as the erectile dysfunction drug Viagra.

Bayer has some data-supported arguments for Adempas--and did we mention that it's a pill? But Actelion has a Tracleer follow-up on its way, developed with United Therapeutics, dubbed Opsumit (macitentan). Actelion filed for FDA approval of Opsumit last year, and it expects a decision before the end of 2013. United Therapeutics had been developing an oral version of Remodulin, but it got its second complete response letter from the FDA recently.

Adempas and Opsumit (as well as Tracleer) work via different mechanisms. Opsumit and Tracleer are endothelin receptor agonists (ERAs), while Adempas stimulates guanylate cyclase. Tracleer goes off patent in 2015, and Actelion hopes Opsumit can take up the slack; a dual ERA, it's considered to be a safer option, with lower risks of liver-related side effects.

Bayer says its new drug is the first to deliver "robust efficacy" in PAH, and the FDA notes that it's the first ever shown effective for patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). It won an advisory panel's endorsement last month, even at a higher dose that made the FDA wary; the agency went with the committee's judgment and cleared dosing up to 2.5 mg.

Analysts figure Adempas can top $700 million by 2018, and some see it leading the pulmonary hypertension market. Others, however, give the long-term advantage to Opsumit, which they see as a first-line therapy in PAH, with Adempas second in line for that indication. In CTEPH, however, Adempas will be the only approved drug. Generic versions of Tracleer and other rivals are coming down the pike within a few years, though, so lower-priced competition is on its way.

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