Sildenafil (Viagra, Revatio) is a PDE5 inhibitor which was approved by FDA for the treatment of erectile disfunction and adults with pulmonary arterial hypertension. Upon administration sildenafil inhibits PDE5 and results in elevated level of cyclic guanosine monophosphate and smooth muscle relaxation.

Udenafil is a new phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction. Udenafil inhibits the cyclic GMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of Cyclic GMP in the corpus cavernosum located around the penis. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. So the inhibition of phosphodiesterase type 5 (PDE5) by Udenafil enhances erectile function by increasing the amount of Cyclic GMP. Udenafil has proven to have high efficacy and a favorable safety profile for a broad spectrum of erectile dysfunction patients, which are comparable to those of other PDE5Is. Due to the clinical properties of relatively rapid onset and long duration of action, Udenafil may be a better option for erectile dysfunction treatment according to patient-specific sex-life patterns. Udenafil is as effective in the treatment of diabetes mellitus-associated erectile dysfunction as other PDE5Is. Recent data suggest that the concomitant use of anti-hypertensive drugs does not significantly affect the efficacy and safety profile. Also, due to its clinical properties, Udenafil can be a daily-dosing option for the treatment of erectile dysfunction, as suggested by its favorable efficacy and safety profile. Udenafil has been approved in South Korea and will be marketed under the brand name Zydena.