Three of these pathways are important since they have been targeted with drugs - endothelin receptor antagonists , phosphodiesterase type 5 ( PDE-5 ) inhibitors , and prostacyclin derivatives .
These pathways correspond to important therapeutic targets in this condition and play a role in determining which of three classes of drugs - endothelin receptor antagonists , phosphodiesterase type 5 inhibitors , and prostacyclin derivatives - will be used .