Viagra

Sildenafil selectively inhibits PDE5, the enzyme responsible for degrading cyclic guanosine monophosphate (cGMP) in smooth muscle cells. By inhibiting this enzyme, sildenafil prolongs cGMP signaling and enhances smooth muscle relaxation in response to nitric oxide.

Key pharmacological mechanisms include:

Vascular smooth muscle relaxation: Supports increased blood flow in responsive vascular tissues.

Erectile function: Enhances blood flow to the corpus cavernosum during sexual stimulation, facilitating erection.

cGMP signaling: Prolongs a physiological pathway involved in vascular smooth muscle relaxation.

Stimulus-dependent activity: Enhances the erectile response to sexual stimulation rather than directly initiating sexual desire.

Sildenafil does not independently produce sexual arousal, increase libido, or guarantee an erection.

Erectile Dysfunction (ED)

Sildenafil is indicated for erectile dysfunction associated with a range of underlying causes, including vascular, metabolic, neurological, and psychological factors.

By enhancing the physiological erectile response, sildenafil can improve the ability to achieve and maintain an erection during sexual activity.

Treatment effectiveness varies according to the underlying cause of ED, individual health status, medication interactions, and other contributing factors.

Pulmonary Arterial Hypertension

Sildenafil is also used in a separate clinical context to treat pulmonary arterial hypertension (PAH), a condition involving elevated pressure in the pulmonary arteries. In this setting, sildenafil acts on PDE5-mediated pathways in pulmonary vascular smooth muscle to promote vasodilation.

PAH treatment uses specific prescribing protocols and formulations. The Viagra brand and its erectile dysfunction dosing instructions should not be substituted for a PAH treatment regimen.