What is the main MOA of Sildenafil (Viagra) and Vardenafil (Levitra)?

What is the main MOA of Sildenafil (Viagra) and Vardenafil (Levitra)?

• A. Inhibit PDE-5
• B. Decrease nitric oxide synthesis
• C. Inhibit PDE-3
• D. Inhibit phosphodiesterase-4

Answer: (A)

Sildenafil and vardenafil work by blocking the enzyme that breaks down a key messenger in penile erection. When a man is sexually stimulated, nitric oxide is released and increases levels of cyclic GMP (cGMP) in the smooth muscle of the penis. The rise in cGMP causes the smooth muscle to relax, allowing more blood to flow in and an erection to form. PDE-5 normally degrades cGMP, terminating the signal. By inhibiting PDE-5, these drugs keep cGMP levels higher for longer, enhancing and sustaining the erection. They are selective for PDE-5, which is why they primarily affect penile blood flow rather than other tissues. They do not decrease nitric oxide synthesis, and they do not inhibit PDE-3 or PDE-4, which are involved in different physiological processes. A practical note: they should not be used with nitrates, as combining them can cause dangerous drops in blood pressure.

Sildenafil and vardenafil work by blocking the enzyme that breaks down a key messenger in penile erection. When a man is sexually stimulated, nitric oxide is released and increases levels of cyclic GMP (cGMP) in the smooth muscle of the penis. The rise in cGMP causes the smooth muscle to relax, allowing more blood to flow in and an erection to form. PDE-5 normally degrades cGMP, terminating the signal. By inhibiting PDE-5, these drugs keep cGMP levels higher for longer, enhancing and sustaining the erection.

They are selective for PDE-5, which is why they primarily affect penile blood flow rather than other tissues. They do not decrease nitric oxide synthesis, and they do not inhibit PDE-3 or PDE-4, which are involved in different physiological processes. A practical note: they should not be used with nitrates, as combining them can cause dangerous drops in blood pressure.