Apr. 1, 1998 March 27, 1998 -- The Food and Drug Administration today announced the approval of Viagra (sildenafil citrate), the first oral pill to treat impotence, a dysfunction that affects millions of men in the United States.
Unlike previously approved treatments for impotence, Viagra does not directly cause penile erections, but affects the response to sexual stimulation. The drug acts by enhancing the smooth muscle relaxant effects of nitric oxide, a chemical that is normally released in response to sexual stimulation. This smooth muscle relaxation allows increased blood flow into certain areas of the penis leading to an erection.
Viagra was evaluated in numerous randomized, placebo controlled trials involving more than 3000 men with varying degrees of impotence associated with diabetes, spinal cord injury, history of prostate surgery, and no identifiable organic cause of impotence. Patients also had a wide range of other concomitant illnesses including hypertension and coronary artery disease.
The drug's effectiveness was assessed primarily using a sexual function questionnaire. Patients were asked to report at the beginning, and periodically throughout the studies, how often they were able to achieve an erection adequate for intercourse, and how often that erection was maintained after penetration. In addition, patients kept diaries of their sexual histories. In all trials, men on Viagra reported success more often than did men on placebo, and rates of success increased with dose. The findings were consistent in men representing a wide range of severity and etiology of their erectile dysfunction (impotence). Men with diabetes or radical prostate surgery had somewhat less improvement than did other groups.
The recommended dose is 50mg taken one hour before sexual activity; individuals may need more (100mg) or less (25 mg) and dosing should be determined by a physician depending on effectiveness and side effects. The drug should not be used more than once a day.
The most common side effects reported in clinical trials included headache, flushing, and indigestion, which occurred at a slightly higher rate in patients taking the drug than among those taking placebo. Some patients on Viagra (about 3 percent) also reported changes in vision, principally altered color perception.
The drug should not be used with organic nitrates such as nitroglycerin patches or sublingual tablets because the combination may lower blood pressure. The safety and efficacy of using Viagra with other treatments for impotence has not been studied, and the use of such combinations is not recommended.
Viagra confers no resistance to AIDS or other sexually transmitted diseases.
Before taking Viagra, patients are advised to:
- Have a thorough medical history and physical examination to diagnose impotence, determine underlying causes and identify appropriate treatment, and
- discuss the cardiac risk associated with sexual activity prior to initiating any treatment for impotence.
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