Efficacy, Safety, and Pharmacokinetics of Macitentan in Japanese Pediatric Patients With Pulmonary Arterial Hypertension: Prospective, Multicenter, Open-Label Study.

Background: Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR), imposing an increased workload on the right ventricle and ultimately leading to right heart failure. Macitentan is a potent dual endothelin receptor antagonist that blocks both endothelin receptor subtypes A and B, and is approved for adult patients with PAH, but evidence in pediatric PAH patients is limited. Methods and Results: This was an open-label, multicenter, Phase III study enrolling Japanese pediatric PAH patients aged ≥3 months to <15 years. A total of 7 patients were enrolled. Efficacy was evaluated by assessing pulmonary hemodynamics after 24 weeks of treatment, and safety was assessed over a 52-week period. The geometric mean fold change in PVR index (PVRI) at Week 24 was 59.43%, which met the prespecified success criterion of ≤81.6% (primary endpoint). Other pulmonary hemodynamic parameters, including mean PAP, mean right atrial pressure, and total pulmonary resistance, also showed improvement. Additionally, at Week 52, functional outcomes such as 6-minute walk test performance and quality-of-life reports, demonstrated a trend toward improvement. Safety findings were favorable, with no unexpected concerns among the 7 treated participants. Most adverse events were mild to moderate in severity, and none were considered related to macitentan. Conclusions: Macitentan showed clinically meaningful reduction in PVRI and improved pulmonary hemodynamics in Japanese pediatric patients with PAH, with a favorable safety profile over 52 weeks of treatment.