Bosentan in Children With Pulmonary Arterial Hypertension (FUTURE-1)

Inclusion Criteria: Signed informed consent by the parents or the legal representatives. Males or females >= 2 and < 12 years of age. Idiopathic PAH or familial PAH diagnosed by right heart catheterization (Clinical classification of pulmonary hypertension, Venice 2003). World Health Organization (WHO) functional class II or III. Oxygen saturation (SpO2) >= 88% (at rest, on room air). PAH treatment-naïve patients or patients already treated with either: Bosentan monotherapy Intravenous epoprostenol monotherapy Intravenous or inhaled iloprost monotherapy Combination of bosentan and intravenous epoprostenol Combination of bosentan and intravenous or inhaled iloprost. All patients should start the study drug (bosentan pediatric formulation) at 2 mg/kg twice daily (b.i.d.), whether or not they were previously treated with bosentan. PAH therapy stable for at least 3 months prior to Screening. Stable treatment with calcium channel blockers, if any, for at least 3 months prior to Screening. Patient's PAH condition stable for at least 3 months prior to Screening. Exclusion Criteria: PAH associated with conditions other than idiopathic or familial PAH. Non-stable patients, e.g., history (in the last 3 months prior to Screening) of recurrent syncope, or signs and symptoms of non-compensated right heart failure. Need or plan to wean patients from intravenous epoprostenol, or intravenous, or inhaled iloprost. Body weight < 4 kg. Systolic blood pressure < 80%, the lower limit of normal range, according to age and gender. AST and/or ALT values > 3 times the upper limit of normal ranges. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C. Hemoglobin and/or hematocrit levels < 75% of the lower limit of normal ranges. Pregnancy. Known intolerance or hypersensitivity to bosentan or any of the excipients.