TUESDAY, June 29, 2004 (HealthDayNews) -- A drug that acts on the hormonal level promises to improve the sex life of women as well as men, and it has moved out of the laboratory into human trials.
The drug, prosaically designated PT-141, acts in a different way than Viagra and its chemical cousins, now marketed for male impotence, said Dennis Earle, director of business development and strategic planning for Palatin Technologies Inc., a New Jersey company that is overseeing those human trials. It also seems to act differently in males and females.
"The biggest difference is that PT-141 is a centrally acting agent," Earle said. It is believed to act on receptors for a hormone called melanocortin, which are found in the brain and elsewhere in the body. Viagra and its competitors increase blood flow to the penis and are not known to affect female sexual activity.
PT-141 definitely affects the sexual behavior of female rats, according to a report in this week's issue of the Proceedings of the National Academy of Sciences by a group led by James G. Pfaus, a professor of psychology and neuroscience at Concordia University in Canada.
Female rats given the drug and placed in a chamber with a male showed a marked increase in behaviors intended to solicit sexual contact, such as hopping and darting, the report said.
"It was a very dramatic increase, which was something I had not seen any other drug do," Pfaus said.
At the University of Washington, Dr. Hunter Wessells, an associate professor of medicine, said the drug had caused an increase in erections when given to men in the form of a nasal spray.
It's not surprising that the drug could affect sexual activity in both males and females, Wessells said. Hormones such as melanocortin "play a significant role in controlling central responses to a number of basic functions," he said. "We're tapping into existing wiring."
But PT-141 does act differently in males and females, Wessells said.
"The interesting thing is that in men it induces erections but doesn't seem to have a significant effect on sexual desire," he said. "In female rats, we get a different response pattern that may translate into a usable drug for female sexual dysfunction."
Wessells is taking part in human tests of the drug, which is moving ahead for both men and women.
Trials are more advanced for men, Earle said. Two major studies, one to include 240 participants, the other with 210, are under way, he said. The hope is that they will lead to the start by mid-2005 of the Phase 3 trials needed for U.S. Food and Drug Administration marketing approval, he said.
Two smaller trials are under way in women, with 24 participants in each. Tests measure increased blood flow to the vagina as a marker of sexual appetite. If the trials go well, studies in which women take the drug home to determine its effect on sexual activity could begin by the first quarter of next year, Earle said.
If PT-141 works as hoped, there would both male and female customers, he said. PT-141 would fill an unmet need for women, while marketing data indicate that 50 percent of men who get first prescriptions for erectile dysfunction never get a second prescription, Earle said.
"Presumably, in some portion of those men, the drug is not working or the men are not able to tolerate the side effects," he said.
Go to the National Library of Medicine to read about female sexual dysfunction.