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

The selection of the starting dose for pediatric participants is based on the PK extrapolation from adults, taking into account the children body weight category, in order to lead to an exposure similar to that in adult PAH participants at a starting dose of 200 micrograms (mcg). As in adults, selexipag will be up-titrated to the individual maximum tolerated dose (iMTD) during the first 12 weeks. Approximately 60 participants will be enrolled in 3 different age cohorts to obtain at least 45 participants with evaluable PK profiles: Cohort 1: \>= 12 to \< 18 years of age, Cohort 2: \>= 6 to \< 12 years of age, Cohort 3: \>= 2 to \< 6 years of age. In each age cohort the starting dose will depend on the body weight. Enrollment will start with both Cohort 1 and Cohort 2. After completion of PK assessments in at least 15 participants from Cohort 1 at Week 12, a first interim analysis will be conducted to establish the dose-exposure relationship using a population PK model. The PK data from any participants in Cohort 2 who have completed their PK assessments at this time will be included in this first interim analysis. Results of this model-based analysis will be used to confirm or adjust the selexipag doses initially selected. Enrollment of Cohort 3 (children \>= 2 to \< 6 years of age) will start once the appropriate doses have been confirmed in a second interim analysis of PK data from Cohorts 1 and 2, and if there is no safety concern based on review by an Independent Data Monitoring Committee (IDMC).