- Subjects who are currently receiving any forms of chronic treatment for PAH such as prostacyclin, PDE-5 inhibitors, endothelin-receptor antagonists, nitrates or nitric oxide donors (e.g. arginine supplement, nicorandil) in any form, protease inhibitors such as ritonavir and saquinavir, ketoconazole, itraconazole, and alpha blockers. Subjects previously receiving any of these drugs must have stopped use for a period of at least 1 month prior to screening, except in the case of bosentan or prostacyclin (3 months).