Avanafil is a selective phosphodiesterase 5 (PDE5) enzyme inhibitor used for the treatment of erectile dysfunction caused by diabetes, age induced oxidative stress or other complications. Avanafil inhibits the cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum located around the penis. Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and corpus cavernosal smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. The inhibition of phosphodiesterase type 5 (PDE5) by avanafil enhances erectile function by increasing the amount of cGMP.
Avanafil is a strong, competitive inhibitor of PDE5. It is also 100-times more potent for PDE5 than PDE6. The IC50 of avanafil is 5.2 nM. Compared to other PDE5 inhibitor like sildenafil and vardenafil, it is 16- and 21-fold more selective for PDE5 respectively. Avanafil does not bind to PDE6 and PDE11 to a considerable degree. The impact of this finding is that avanafil is less likely to cause side effects such as visual disturbances and myalgia. These are side effects that patients on sildenafil or tadalafil are more likely to experience. Furthermore, single oral doses of avanafil (200 mg) administered to healthy male volunteers resulted in mean changes from baseline in systolic/diastolic blood pressure of -5.3/-3.7 mmHg at 1 hour after dosing. Avanafil does not causes changes in QTc interval or ventricular repolarization.
Avanafil is hepatically metabolized primarily by the enzyme, CYP3A4. Two major metabolites are formed, M4 and M16. M4 has 4% of the pharmacologic activity of avanafil. M16 is an inactive metabolite.
Avanafil is generally well tolerated. The most commonly reported adverse event are headache and facial flushing.
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