Sildenafil citrate

Sildenafil is a potent, selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5). Sildenafil is used to treat erectile dysfunction and pulmonary arterial hypertension. NO activates guanylate cyclase, which results in increased levels of cGMP, producing smooth muscle relaxation. Sildenafil enhances the effect of NO by inhibiting PDE5, which is responsible for degradation of cGMP.