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SUMMARY:
Sildenafil inhibits phosphodiesterase type V, thereby amplifying the erectile response to sexual stimulation via a decrease in the breakdown of cGMP, the intracellular second messenger of a major neuromediator of erection, nitric oxide. This drug has initiated a revolution in the management of many cases of erectile dysfunction (ED); it is the first oral treatment with proven efficacy when taken as needed, one hour before planned intercourses, provided that sexual stimulation is present.

A number of objective studies have established the efficacy of sildenafil, which is much higher than that of a placebo. While exerting no direct effect on sexual desire, sildenafil increases the subject's capacity to achieve and maintain a rigid erection. Sexual satisfaction of both partners is markedly improved. A dose-effect relationship is observed up to 100 mg and sidenafil maintains its efficacy during two years or more. Efficacy is maximal in ED cases without significant organic causes (85-90% of patients reported improved erections) and is less marked in populations of patients with primarily organic ED (% of patients reporting improved erections: paraplegics, 86%; diabetics, 59%; radical prostatectomy patients, 43%). The drug is generally well tolerated (incidence rate of headache, flushing and gastrointestinal disorders: 6-10% for each). Silenafil has no serious adverse effects, provided that interaction with nitrates or nitric-oxide-providers is avoided.