The Food and Drug Administration, acting with unusual speed Friday, approved the first pill to treat impotence, which health officials estimate affects millions of men in this country.
The oral medication, Viagra, which will be available only by prescription, is the first nonsurgical approach to treatment of sexual dysfunction. It is being touted as easier and less embarrassing for men to use than currently available treatments, which must be injected or inserted into the penis.
Drug industry analysts have estimated that Viagra's sales could reach $500 million by 2003.
Viagra is taken by mouth about an hour before intercourse and does not directly cause penile erections. Rather, it affects the response to sexual stimulation.
Essentially, the drug enhances 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.
"This new therapy increases the range of options available for men with this problem," said Dr. Janet Woodcock, director of the FDA's center for drug evaluation and research. "Nothing works for everyone, but this will be another choice, a medication that can be taken conveniently.
"There has been a great interest on the part of the consumer public in having new therapies for impotence, judging from the mail and the inquiries about it that we have received. . . . [Impotence] has a large impact on peoples' lives, but it is not widely discussed like other conditions."
The drug, manufactured by New York-based Pfizer Pharmaceuticals, is expected to be available in pharmacies within a month, the FDA said. The company has estimated the wholesale price at $7 a pill.
It is the first of several oral medications for impotence in the pipeline to be approved by federal regulators, who moved rapidly, licensing the drug only six months after the company submitted its application.
Between 10 million and 20 million men are believed to experience impotence at some time during their lives, particularly middle-age or elderly men. Impotence can result from organic causes, such as diabetes, arteriosclerosis and prostate ailments, or as a side effect of medication. It also can stem from psychological factors.
The drug was tested and found effective in both physical and psychological cases.
Health officials stressed that the pill is not designed for healthy men seeking to increase or improve their sexual activity.
Dr. Harin Padma-Nathan, director of the Male Clinic in Santa Monica, one of the researchers who studied the drug, said that Viagra "is a medical therapy for a medical problem. It improves erections to nearly normal but not normal. It does not have the potential to alter erections in normal men, and it does not alter libido or desire. Therefore, it is not an aphrodisiac."
Padma-Nathan termed the drug "a revolutionary medical therapy," adding: "It is not a sexual revolution."
Padma-Nathan, clinical associate professor of urology at USC, said that Viagra was effective in up to 89% of those whose dysfunction was the result of psychogenic problems and up to 70% in those whose impotence resulted from physical causes.
The pill should not be used more than once a day, the FDA said.
The recommended dose is 50 milligrams, but some individuals may need as much as 100 milligrams or as little as 25 milligrams, a decision that should be determined by a physician based on effectiveness and the degree of side effects, the agency said.
FDA officials said that Viagra, known chemically as sildenafil citrate, appeared to cause few side effects. The most common reported in clinical trials were headache, flushed skin and indigestion, which occurred at a slightly higher rate in patients taking the drug than among those taking a placebo. About 3% of patients taking Viagra also reported vision changes, specifically altered perception of color.
Viagra was tested in clinical trials involving more than 3,000 men with varying degrees of impotence associated with diabetes, spinal-cord injury, a history of prostate surgery or no readily identifiable organic cause. Patients in the studies also suffered from a wide range of other illnesses, including hypertension and heart disease.
The agency warned that the drug must not be used with organic nitrates, such as nitroglycerin patches or sublingual tablets, because the combination could lower blood pressure. The agency also cautioned against using the product with other therapies for impotence, saying that the combinations have not been studied.
The drug's effectiveness was evaluated primarily through self-reporting via a sexual function questionnaire completed by study participants.
They were asked to report at the beginning and periodically throughout the studies how often they were able to achieve an erection sufficient for intercourse and how often the erection was maintained after penetration. Also, patients kept diaries of their sexual histories.
In all of the trials, the men taking Viagra reported success more often than those on the placebo, and the rates of success increased with dosage, the FDA said.