A Phase 3 Study of Extended-release Tacrolimus in Subjects With Pulmonary Arterial Hypertension and Functional Limitations

Inclusion Criteria: * WHO Group 1 PH: Pulmonary Arterial Hypertension; * WHO functional class II - IV despite optimized treatment with one or more modalities. Treatments for PAH must be stable for at least 3 months at the time of screening; * Right heart catheterization (RHC) at screening (or within 3 months prior to screening); * Screening 6MWD \>75 meters to ≤450 meters. Exclusion Criteria: * PAH due to pulmonary veno-occlusive disease or pulmonary capillary hemangiomatosis * Chronic thromboembolic or portopulmonary hypertension * Total Lung Capacity (TLC) \<60% predicted; * FEV1/FVC \<70% predicted or FEV1 \<60% predicted; * Evidence of left-sided heart disease; * Inability to safely attempt completion of the 6MWD; * Life expectancy \<6 months; * eGFR \<30 mL/min/1.73 m2 (CKD-EPI equation); * Moderate to severe hepatic dysfunction (Child-Pugh score \>10); * Serum potassium \>5.1 mEq/L; * Use of experimental PAH treatments within the past 3 months; * Active infection requiring antibiotic, antifungal, or antiviral therapies; * Current systemic treatment with cyclosporine; * Known allergy or hypersensitivity to tacrolimus; * Significant psychiatric, addictive, or other disorder that compromises the subject's ability to provide informed consent, follow study protocol, or adhere to study treatment