Which endothelin receptor antagonist is used in pulmonary arterial hypertension?

Ambrisentan is an endothelin receptor antagonist specifically approved for the treatment of pulmonary arterial hypertension (PAH). This medication works by blocking endothelin-1, a potent vasoconstrictor, thereby leading to vasodilation and improved blood flow in the pulmonary and systemic circulation. By reducing the effects of endothelin-1, ambrisentan helps to lower blood pressure in the pulmonary arteries and improves exercise capacity in patients with PAH.

Other options mentioned, such as riociguat, tadalafil, and selexipag, are all used in the management of pulmonary arterial hypertension but belong to different classes of medications. Riociguat is a soluble guanylate cyclase stimulator, tadalafil is a phosphodiesterase-5 inhibitor, and selexipag is a selective prostacyclin receptor agonist. While these medications are effective treatments for PAH, they do not function as endothelin receptor antagonists. Therefore, ambrisentan is the only option that directly represents the correct class of drug used in this indication.