Sildenafil in PH
The NO stimulates the formation of cGMP in the smooth muscle cells of the lung artery walls, which induces muscle relaxation by decreasing the intracellular calcium concentration. The drug sildenafil(Revatio®) is a selective inhibitor of the enzyme phosphodiesterase-5 (PDE-5), thereby maintaining high cGMP levels and thus relaxation of the vascular smooth muscle cells.
Compare this mechanism of action with that of nitrates in vasodilation. You will understand that co medication with nitrates will enlarge the vasodilating effect of sildenafil.
The adverse effects of sildenafil result from the vasodilating mechanism and include headache, flushing and dizziness.
EPAR of sildenafil.