A Clinical Study of to Confirm the Doses of Selexipag in Children With Pulmonary Arterial Hypertension

Prior treatment

• Previous treatment with Uptravi (selexipag) within 2 weeks prior to enrollment
• Participants having received prostacyclin (epoprostenol) or prostacyclin analogs (that is, treprostinil, iloprost, beraprost) within 2 months prior to enrollment or are scheduled to receive any of these compounds during the trial
• Treatment with another investigational drug within 4 weeks prior to enrollment
• Clinical signs of hypotension that in the investigator's judgment would preclude initiation of a PAH-specific therapy

Other illness

• Participants with PAH due to portal hypertension, schistosomiasis, pulmonary veno-occlusive disease (PVOD) and/or pulmonary capillary hemangiomatosis
• Participants with PAH associated with Eisenmenger syndrome
• Participants with cyanotic congenital cardiac lesions such as transposition of the great arteries, truncus arteriosus, univentricular heart or pulmonary atresia with ventricular septal defect, as well as Participants with Fontan-palliation
• Participants with pulmonary hypertension due to lung disease
• Uncontrolled thyroid disease as per investigator judgment
• Known severe or moderate hepatic impairment
• Participants with severe renal insufficiency
• Known hypersensitivity to the investigational treatment or to any of the excipients of the drug formulations

Lab values

• Hemoglobin or hematocrit \< 75 percentage (%) of the lower limit of normal range

Other

• Participants with moderate to large left-to-right shunts
• History, or current suspicion of intussusception or ileus or gastrointestinal obstruction as per investigator's judgment

• Signed and dated informed consent by the parent(s) or Legally authorized representative(s) AND assent from developmentally capable children
• Males or females between greater than or equal to (\>=) 2 and less than (\<) 18 years of age with weight \>= 9 kilograms (kg)
• Pulmonary arterial hypertension (PAH) diagnosis confirmed by documented historical right heart catheterization (RHC) performed at any time before participant's enrollment
• PAH with one of the following etiologies:
  • idiopathic (iPAH),
  • heritable (hPAH),
  • associated with congenital heart disease (CHD): PAH with co-incidental CHD; post-operative PAH (persisting/ recurring/ developing \>= 6 months after repair of CHD)
  • Drug or toxin-induced
  • PAH associated with HIV
  • PAH associated with connective tissue disease
• Word Health Organization functional class (WHO FC) II to III
• Participants treated with an endothelin receptor antagonist (ERA) and/or a phosphodiesterase type 5 (PDE-5) inhibitor provided that the treatment dose(s) has been stable for at least 3 months prior to enrollment, or participants who are not candidates for these therapies
• Females of childbearing potential must have a negative pregnancy test at Screening and at Enrollment, and must agree to undertake monthly pregnancy tests, and to use a reliable method of contraception (if sexually active) from screening up to study drug discontinuation plus 30 days (EOS)