Repurposing a Histamine Antagonist to Benefit Patients With Pulmonary Hypertension

Inclusion Criteria: * Male or female, age 18 to 80 * WHO Group 1 Pulmonary Arterial Hypertension * NYHA Functional Class II, III, or IV at screening * Stable dose of pulmonary vasodilators for 30 days prior to randomization * Right heart catheterization within five years demonstrating a mean pulmonary arterial pressure of ≥ 25 mmHg, occlusion pressure of ≤ 15 mmHg, and pulmonary vascular resistance of ≥ 3 wood units * Participants with a right heart catheterization within five years demonstrating a mean pulmonary arterial pressure of ≥ 25 mmHg and occlusion pressure of 15 - 20 mmHg will be considered for inclusion if the pulmonary vascular resistance ≥ 9 wood units and they are being treated with pulmonary arterial hypertension specific therapy * Able to walk with/without a walking aid for a distance of at least 50 meters Exclusion Criteria: * Pregnant or lactating * Non-group 1 pulmonary hypertension or veno-occlusive disease * History of interstitial lung disease, unless subject has collagen vascular disease and has pulmonary function testing conducted within 12 months demonstrating a total lung capacity of ≥ 60 % * Has received or will receive an investigational drug, device, or study within 30 days or during the course of study * Left sided myocardial disease as evidenced by left ventricular ejection fraction \< 40% * Any other clinically significant illness or abnormal laboratory values (measured during the Screening period) that, in the opinion of the Investigator, might put the subject at risk of harm during the study or might adversely affect the interpretation of the study data * Anticipated survival less than 1 year due to concomitant disease * Regularly taking an H2 receptor antagonist within 30 days of enrollment * Creatinine clearance \< 30 mL/min * History of bariatric surgery * Current treatment for HIV