BRIEF-Actelion says initiates phase III study to evaluate macitentan (opsumit) in children with PAH

* Says initiates phase III study to evaluate macitentan (opsumit) in children with pulmonary arterial hypertension. Source text for Eikon: [https://www1.actelion.com/en/our-company/news-and-events.page?newsId=2025902&bb=js ] Further company coverage: (Reporting By Zurich newsroom)...