Phosphodiesterase-5 Enzyme Inhibitors
The antiproliferative effects of the phosphodiesterase type 5 (PDE5) pathway, which regulates cyclic guanosine monophosphate (cGMP) hydrolysis, may be significant in the long-term treatment of PAH with PDE5 inhibitors such as sildenafil.
Sildenafil promotes selective smooth-muscle relaxation in lung vasculature, possibly by inhibiting PDE5. This results in a subsequent reduction of blood pressure in pulmonary arteries and an increase in cardiac output.
Tadalafil is a PDE5 inhibitor indicated for improving exercise capacity in patients with WHO group 1 PAH. It increases cGMP, the final mediator in the nitric oxide pathway.
Vardenafil (Levitra, Staxyn ODT)
Vardenafil is a PDE5 inhibitor. This medication has been demonstrated to increase 6-minute walk distance. It is dosed as once or twice daily.