Endothelin Receptor Antagonists
Endothelin receptor antagonists include bosentan (Tracleer) and ambrisentan (Letairis). Endothelin receptor antagonists vasodilate and prevent cell growth in the arteries by preventing endothelin from activating receptors. Bosentan blocks the endothelin-A and endothelin- B receptors, thereby causing vasodilatation. It is administered orally and has been approved for Classes II, III, and IV. The drug can be toxic to the liver and cause birth defects. All patients on this medication must receive monthly liver function tests, and women must have a negative pregnancy test before initially starting the medication.
A monthly pregnancy test should be obtained while the patient is on this medication. Ambrisentan is administered orally and only blocks the endothelin-A receptor. It has been approved for functional Class II and III. Pregnancy tests must also be collected monthly for women taking this medication.