シルデナフィル

Sildenafil white crystalline powder, with a molecular formula of C22H30N6O4S and a density of 1.39g/cm3, also known as sildenafil, is a male erectile dysfunction drug accidentally invented during the development of cardiovascular disease drugs. It is widely known under its commercial name Viagra.

Pharmacodynamics

Effect of Sildenafil on Penile Erection Response

Sildenafil (Viagra) is a highly selective phosphodiesterase type 5 (PDE5) inhibitor. PDE5 is highly expressed in penile corpus cavernosum tissue, while its expression is low in other tissues (including platelets, vascular and visceral smooth muscle, and skeletal muscle). By selectively inhibiting PDE5, Sildenafil enhances the nitric oxide (NO)-cGMP pathway, increasing cGMP levels, which leads to relaxation of penile corpus cavernosum smooth muscle, enabling patients with erectile dysfunction to achieve a natural erectile response to sexual stimulation.

The erectile response generally increases with Sildenafil dosage and plasma concentration. Studies show that the pharmacodynamic effect lasts up to 4 hours, though the response is weaker compared to that at 2 hours.

Effect of Sildenafil on Myocardial Response

PDE5 is absent in normal or diseased cardiac conduction tissue, cardiomyocytes, endothelial cells, and lymphoid tissue. Therefore, Sildenafil (a PDE5 inhibitor) has no positive inotropic effect and does not directly affect myocardial contractile function.

シルデナフィル

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