Actelion has been boosted by the news that regulators in the USA have officially accepted a New Drug Application for macitentan, the successor to the Swiss biotech's blockbuster Tracleer.

A filing was made to the US Food and Drug Administration in October for macitentan (which will be sold, if approved, as Opsumit) as a treatment for  pulmonary arterial hypertension. The review period is expected to last 12 months.

The file for Opsumit, a novel oral dual endothelin receptor antagonist, is based on data from a 742-patient Phase III trial. In the study, called SERAPHIN, the risk of a morbidity and mortality event was reduced by 45% for patients in the Opsumit 10mg dose group and by 30% for those on the 3mg dose compared to those on placebo.

Actelion hopes the drug will replace its flagship drug Tracleer (bosentan), which makes up the vast majority of its turnover but goes off-patent in 2015. Sales of Tracleer for the first nine months of 2012 decreased 4% to 1.13 billion Swiss francs, with the fall being principally due to Gilead Sciences' rival drug Letairis (ambrisentan).

Actelion chief executive Jean-Paul Clozel said "we are very happy that this very large dossier was accepted by the FDA and that we are another step closer to our goal of bringing this drug to patients with this life- threatening disease".