Bosentan. Bosentan, N-[6-(2-hydroxyethoxy)-5-(2-methoxyphenoxy)-2-pyrimidin-2-yl-pyrimidin-4-yl]-4-tert-butyl-benzenesulfonamide (Tracleer, Bozentan), was the first endothelin receptor antagonist marketed in the United States. Bosentan works by competitively blocking the endothelin receptor subtypes ETA and ETB. In binding to the receptors, it blocks the effects of endothelin, which include constriction of the vascular smooth muscle, which leads to narrowing of the blood vessels and hypertension. Although it is not selective for the ETA receptors, it does have a higher affinity for that subtype over ETB. However, the clinical significance of selectivity over preferential receptor binding has not been demonstrated. Bosentan is an inducer of CYP2C9 and CYP3A4, and patients using bosentan must be monitored for liver toxicity. 50
Sitaxsentan Sodium. Sitaxsentan, N-(4-chloro-3-methyl-oxazol-5-yl)-2-[2-(6-methylbenzo[1,3]dioxol-5-yl)acetyl]thiophene-3-sulfonamide (Thelin), belongs to the sulfonamide class of endothelin receptor antagonists.
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