Bosentan is a/an:
**Core Concept**
Bosentan is an endothelin receptor antagonist (ERA) used in the treatment of pulmonary arterial hypertension (PAH). It acts by blocking the action of endothelin-1 (ET-1), a potent vasoconstrictor peptide that plays a key role in the pathophysiology of PAH.
**Why the Correct Answer is Right**
Bosentan works by competitively inhibiting the binding of endothelin-1 to its receptors on vascular smooth muscle cells, leading to vasodilation and a decrease in pulmonary vascular resistance. This results in improved exercise capacity and hemodynamics in patients with PAH. Bosentan is a dual endothelin receptor antagonist, targeting both ETA and ETB receptors.
**Why Each Wrong Option is Incorrect**
**Option A:** Bosentan is not a calcium channel blocker, which is a different class of drugs used to treat hypertension and PAH.
**Option B:** Bosentan is not a phosphodiesterase-5 inhibitor (PDE5 inhibitor), which includes drugs like sildenafil used in the treatment of erectile dysfunction and PAH.
**Option C:** Bosentan is not a prostacyclin analogue, which includes drugs like epoprostenol used in the treatment of PAH.
**Clinical Pearl / High-Yield Fact**
Bosentan is known to cause liver enzyme elevations and should be used with caution in patients with pre-existing liver disease. Regular monitoring of liver function tests is recommended.
**Correct Answer: C. Endothelin receptor antagonist.**