By Maggie Fox, Health and Science Correspondent
WASHINGTON, March 5 (Reuters) - Viagra, the blockbuster impotence drug that has transformed the sex lives of millions of men, does not work so well in women, a small study published on Friday finds.
A team at Columbia Presbyterian Center in New York found that Viagra, made by Pfizer Inc. (NYSE:PFE - news), has no more of an effect in women than a dummy pill would.
``We found that the majority of women did not really have what you would say is a big dramatic response," Dr. Steven Kaplan, a urologist who led the study, said in a statement.
"We found that there was no significant change either in intercourse satisfaction or in the degree of sexual desire after the patients had taken Viagra for 12 weeks," he added. "Even though about 25 percent of the patients had some improvement in overall sexual function, that's equal to the placebo response in men receiving Viagra."
Kaplan's study in the journal Urology is the first published study of Viagra in women, although several others are being conducted.
Viagra, known generically as sildenafil, works by increasing the effects of nitric oxide, a common body chemical, which in turn gets more blood flowing into the genitals. Doctors have said theoretically it should work the same way for women -- helping sexual function once a person is aroused.
Kaplan tested the drug in 33 women past menopause, most in their 50s, who said they had suffered sexual problems for at least six months. With menopause women often report decreased sensation and lubrication, making sex difficult and sometimes uncomfortable.
Each one took 50 mg of Viagra, the same dose of the blue, diamond-shaped pill that men get -- an hour before sex.
"Viagra did appear to increase blood flow to the clitoris, but this didn't seem to translate to increased sexual satisfaction," Kaplan said.
Seven of the patients said they became too sensitive, and three pulled out of the study because of it. Kaplan said only seven percent of the women said they found it easier to reach orgasm, and just 20 percent wanted to keep taking Viagra after the three-month trial was over.
Other researchers have reported that in a few cases the drug does work well for women. A team at Boston University is testing Viagra in women, as well as Vasomax, made by Zonagen Inc. (Nasdaq:ZONA - news) and licensed to Schering-Plough Corp. (NYSE:SGP - news), and other drugs.
Pfizer has studies in women underway, as well.
"Pfizer is the expert on Viagra," Corey Davis, a drug industry analyst at Hambrecht and Quist, said. "Pfizer knows which patients to target ... they know how to make a clinical trial work."
Kaplan agreed his patients may not have been optimal Viagra patients, but said his 33 volunteers reflected the real world.
"We just took all comers, if you will," he said. "The women had what they described as sexual dysfunction, not me."
Pfizer has said Viagra will not work in people who have trouble getting aroused in the first place, and Kaplan said that could have been the problem with many of the women in his study.
He hopes to do more studies on Viagra and other drugs, including perhaps herbal medicine.
Davis said he did not expect such a small study to affect Pfizer's stock. "With only 33 patients it's certainly far from conclusive."
Pfizer stock rose $3.81, about 3 percent, to $136.56 Friday on the New York Stock Exchange, where it was among the top 25 net gainers on the day.
Pfizer says seven million prescriptions have been written for Viagra worldwide, which earned the company $788 million last year.
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