Bayer has announced that it is putting its investigational pulmonary-hypertension compound riociguat into late-stage trials after the drug showed promise in a Phase II study.

The German firm says that its Phase III programme will investigate riociguat in patients with both chronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH). Over 700 patients will be recruited for the two studies, called CHEST-1 and PATENT-1.

The drug is the first member of a new class of therapeutics stimulating the enzyme soluble guanylate cyclase (sGC) and the mid-stage data showed that it significantly improves exercise capacity and “haemodynamic parameters”, Bayer said, such as pulmonary vascular resistance, cardiac output and pulmonary arterial pressure.

Bayer quoted Hossein Ardeschir Ghofrani of the University Hospital Giessen and Marburg, Germany, as saying that CTEPH and PAH are life-threatening diseases but currently available treatments are approved only for the latter “and the median survival time for treated patients is still very limited”. Frank Misselwitz, head of development for cardiovascular diseases at Bayer Schering Pharma, added that “riociguat has the potential to overcome the disadvantages of current standard therapies”.

PAH affects more than 2.5 million people worldwide, and the market is dominated by Actelion's Tracleer (bosentan). If approved, analysts believe riociguat could be a blockbuster.