Sitaxsentan is a selective endothelin receptor antagonist (ET_A) primarily used in the treatment of pulmonary arterial hypertension (PAH), a condition characterized by high blood pressure in the arteries of the lungs. It works by blocking endothelin receptors, preventing the vasoconstrictive effects of endothelin, which helps to relax blood vessels and improve blood flow. This reduces the strain on the heart and alleviates symptoms such as shortness of breath and fatigue. Sitaxsentan was beneficial for patients unresponsive to other treatments but was withdrawn from the market due to risks of severe liver toxicity. It is now available for research purposes and requires careful handling.