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