"The European Medicines Agency will now start the formal review process," Actelion said on Thursday. It plans to sell the drug under the brand name Opsumit.

Actelion, which submitted the treatment to the U.S. health regulator a month ago, issued data last month showing macitentan prolonged overall survival by more than a third in a clinical trial.

The company is banking on macitentan to replace top-seller Tracleer which, like macitentan, also treats pulmonary arterial hypertension (PAH) and currently accounts for around 90 percent of group sales. Tracleer goes off patent from 2015 and faces growing competition from Gilead's Letairis.

Actelion is continuing to prepare macitentan submissions in Switzerland and major markets around the world, the company said.

(Reporting By Katharina Bart; Editing by Dan Lalor)

• A Permanent Economic Emergency