Bayer has launched an offensive on the pulmonary arterial hypertension (PAH) market, filing its riociguat drug candidate for approval in the US and EU.

Riociguat is one of five late-stage drug candidates Bayer expects to add up to 5.5 billion euros ($7bn) in peak sales, with the company predicting last year that riociguat itself could carve out a 500 million euro-plus share of the global PAH market.

The drug has been filed on both sides of the Atlantic as a treatment for patients with PAH as well as a related condition known as inoperable chronic thromboembolic pulmonary hypertension (CTEPH).

If approved riociguat will enter a market dominated by Actelion's endothelin antagonist Tracleer (bosentan) product - which brought in around $1.2 billion in sales in the first nine months of 2012 but is due to lose patent protection in 2015 - and fast-growing rival Letairis/Volibris (ambrisentan) from Gilead Sciences and GlaxoSmithKline.

Gilead reported last week that Letairis sales topped $410 million last year, while GSK said its Volibris brand reached around $215 million. Meanwhile, Actelion's has already filed for approval of Tracleer follow-up Opsumit (macitentan), which is also tipped to be a blockbuster.

Riociguat would be the first drug belonging to the sGC (soluble guanylate cyclase) class to reach the market, and Bayer maintains it has a competitive profile that should allow it to take on the dominance of the endothelin antagonists.

In the PATENT-1 trial, Bayer's drug met its primary objective of improving the six-minute walk distance (6MWD) in PAH patients compared to placebo, improving the average distance covered by 36 metres after 12 weeks' treatment.

Statistically significant improvements were also recorded across a range of secondary endpoints, including pulmonary vascular resistance and time to clinical worsening, while a positive trend was observed on quality of life measures.

A second study called CHEST-1 in CTEPH patients found similar improvements, and to date riociguat is the only drug to have been tested specifically in this form of PAH, which has no approved pharmacological treatment.

"These regulatory submissions for two distinct forms of pulmonary hypertension … fuel our hope to bring this much-needed new treatment option for these serious and potentially fatal diseases to patients and doctors soon," commented Bayer's head of global development Kemal Malik.