Bostentan is a –
**Core Concept**
Bosentan is an endothelin receptor antagonist used in the treatment of pulmonary arterial hypertension (PAH). It works by blocking the action of endothelin-1, a potent vasoconstrictor peptide that plays a key role in the pathophysiology of PAH.
**Why the Correct Answer is Right**
Bosentan is a dual endothelin receptor antagonist, meaning it blocks both ETA and ETB receptors. This blockade results in vasodilation of pulmonary arteries, reducing pulmonary vascular resistance and improving exercise capacity in patients with PAH. Bosentan also has antiproliferative effects, inhibiting the growth of smooth muscle cells and reducing the thickness of the pulmonary vascular wall.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because bosentan is not a phosphodiesterase-5 inhibitor (PDE-5 inhibitor), which is a different class of drugs used in the treatment of PAH, such as sildenafil.
**Option B:** This option is incorrect because bosentan is not a nitric oxide donor, which is another mechanism of action used in the treatment of PAH, such as nitroglycerin.
**Option C:** This option is incorrect because bosentan is not a prostacyclin analogue, which is a different class of drugs used in the treatment of PAH, such as epoprostenol.
**Clinical Pearl / High-Yield Fact**
Bosentan is known to induce liver enzyme elevations, making regular monitoring of liver function tests necessary in patients taking this medication.
**Correct Answer: D. Endothelin receptor antagonist. Bosentan is a dual endothelin receptor antagonist used in the treatment of pulmonary arterial hypertension (PAH).**