Viagra is a well-known preparation indicated for the treatment of erectile dysfunction in men over 18 years of age. The peculiar property of Viagra consists in ability to restore erection in men during 4 hours. Before understanding Viagra action mechanism, it is important to know how occurs erection. Male erection include the following mechanisms: sexual excitement causes human brain to send impulses to the penis. These impulses stimulates the release of nitrogen oxide(NO). Nitrogen oxide binds to specific enzyme called guanylate cyclase and causes the production of cyclic guanosine monophosphate (cGMP).
Cyclic GMP interacts with the smooth muscles in the cavernous tissue and causes their relaxation. This in its turn enhances blood flow to the penis resulting in erection. Being released in the cavernous tissue cGMP is broken down by an enzyme called PDE5. Viagra works by blocking this enzyme and thus increases the amount of cGMP. All of these finally improve blood flow to the male genitals causing strong erection. It is important that Viagra works only in the case of sexual excitement. When the sexual intercourse is finished, male panis naturally returns to its normal relaxation condition. In other words Viagra acts only on natural erection mechanism and this is its undoubted advantage among other erectile dysfunction preparation.
Viagra is available in the form of pills 25 mg, 50 mg and 100 mg. Usually Viagra is taken one hour before sexual intercourse. The average dose is usually 50 mg. The dose for patients with kidney and liver diseases is usually 25 mg. In inefficiency of 50 mg Viagra dose may be increased up to 100mg.
More than 3000 men aged between 19 and 87 years estimated the efficiency of Viagra in clinical trials. The patients were suffering from erectile dysfunction in average 5 years( from 6 month to 26 years). Erectile dysfunction was of a different origin including organic and psychogenic origin. The results of the clinical trials showed tha Viagra is effective in most of patients including those suffering from diabetes, damage of the spinal cord and other functional conditions.