Pulmonary arterial hypertension (PAH) is a life threatening, progressive condition which eventually leads to fatal right heart failure. Endothelin-1 (ET-1), a potent vasoconstrictor peptide, is increased in the pulmonary arteries of patients with pulmonary hypertension. Endothelin-1 acts through the stimulation of 2 subtypes of receptors (endothelin receptor subtypes A [ETA] and B [ETB]). In PAH patients, ETRAs block the deleterious vasoconstrictor effects of ET-1, and ETRA treatment in PAH patients has been shown to be safe and efficacious. Sitaxsentan is an orally active, highly ETA selective ETRA that, in clinical trials, has demonstrated improvements in exercise capacity, functional class and hemodynamics in PAH patients. Sitaxsentan has been shown to be safe, well tolerated, and associated with a lower incidence of liver toxicity than other approved ETRAs
