This study enrolls patients with pulmonary arterial hypertension (PAH) treated with inhaled treprostinil. During the study, the treatment with inhaled treprostinil will be tapered off and simultaneously replaced with an oral treatment (selexipag) targeting the disease in a similar way.

The purpose of the study is

i) to investigate the safety and tolerability of oral selexipag in patients who transition from inhaled treprostinil,

ii) to investigate the effects of oral selexipag on PAH severity and exercise ability before and after transition, and

iii) to gain new information about the patients experience taking oral selexipag compared to inhaled treprostinil.

Study participants may stay in the study until the FDA has granted marketing authorization.