Endothelin receptor antagonists (Bosentan): - Competitively antagonizes endothelin-1 receptors → ↓ pulmonary vascular resistance.- Heptatotoxic (monitor LFTs)

PDE-5 inhibitors (Sidenafil):- Inhibits PDE-5 → ↑ cGMP → prolonged vasodilatory effect of nitric oxide.- Also used to treat erectile dysfunction.- Contraindicated when taking nitroglycerin or other nitrates.

Prostacyclin analogs (Epoprostenol, iloprost):- PGI₂ (prostacyclin) with direct vasodilatory effects on pulmonary and systemic arterial vascular beds. Inhibits platelet aggregation.- Side effects: flushing, jaw pain