• PAH can be classified as primary (PPH) or secondary pulmonary hypertension (SPH)
• Epoprostenol a prostacyclin analog was the first primary drug for patients w/PAH
• Recent clinical trials describe combination therapy as superior in efficacy to traditional monotherapy
• Varied etiologies of PAH hampers the performance of RCTs for each combination therapy
• PAH is associated w/diminished endothelium factor & nitric oxide, increased phosphodiesterase enzyme leading to the development of the ET-1 receptor antagonist (ERA) bosentan and the PDE- V inhibitor sildenafil
• RCTs are currently investigating the efficacy of three news agents in tx of PAH: imatinib, riociguat, and selexipag 

References

A. Yao. Journal of Cardiology 60 (2012) 344–349