Sildenafil citrate is a potent and selective inhibitor of specific phosphodiesterase type 5 (PDE5).
The physiological mechanism of penile erection involves the release of nitric oxide (NO) in the cavernous body with sexual stimulation. Nitric oxide activates the enzyme guanylate cyclase, that leads to an increase in the level of cyclic guanosine monophosphate (cGMP) and, accordingly, relaxation of smooth muscles of the cavernous body, resulting in increased blood flow in the penis.
Sildenafil does not have a direct relaxing effect on an isolated cavernous human body, but actively enhances the relaxing effect of NO on this tissue by inhibiting PDE5, responsible for the disintegration of cGMP in the cavernous body.
This leads to an increase in the level of cGMP, resulting in a relaxation of smooth muscles and increased blood flow in the cavernous body.
Therefore, the use of sildenafil in recommended doses is ineffective in the absence of sexual stimulation.
Effect of sildenafil on erectile dysfunction:
In a double-blind, placebo-controlled, cross-sectional study of patients with erectile dysfunction of various etiologies (organic, psychogenic, mixed), the result of sexual stimulation was the onset of a prolonged erection sufficient for intercourse after sildenafil was administered in comparison with placebo.
Effect of sildenafil on blood pressure:
When using the drug inside at a dose of 100 mg, the maximum decrease in systolic blood pressure (BP) in the prone position was on average 8.4 mm Hg, and the diastolic blood pressure in the prone position was 5.5 mm Hg. Art. More pronounced, but similarly transient effects on blood pressure were observed in patients who simultaneously received nitrates.
Influence of sildenafil on hemodynamics:
A single dose of sildenafil in a dose of 100 mg did not cause clinical significant changes in the ECG in healthy volunteers.
Effect of sildenafil on vision:
In some patients, after 1 hour after taking the drug at a dose of 100 and 200 mg, a mild and transient disregard of color (blue / green) was detected, 2 hours after taking these changes were absent. The established mechanism of color vision disorder is the inhibition of PDE 6, which is involved in the process of light transmission to the retina. Sildenafil has no effect on visual acuity, sensitivity to contrast, intraocular pressure or the diameter of the pupil.