A hysterectomy 11 years ago zapped Colleen Christensen's sexual desire. Now 55 years old and married for 33 years, Christensen said she used to worry that a lack of intimacy was draining the fun and closeness from her relationship.

Two and a half years ago she joined a clinical trial for Intrinsa, a testosterone patch made by Procter & Gamble Co. The effect was almost instantaneous. "Remember when you were young and you got this buzz and you looked at your husband and said 'Oh, baby?'" asked Christensen, a homemaker in Poulsbo, Wash.

On Thursday a U.S. Food and Drug Administration committee will review Intrinsa (search), which could be the first prescription medication to win approval for female sexual dysfunction (search).

P&G's interest in Intrinsa is easy to understand: Viagra (search), Pfizer Inc.'s impotency pill, and its two newer competitors, Cialis from Eli Lilly & Co. and Icos Corp., and Levitra from GlaxoSmithKline PLC and Bayer AG, will account for the bulk of an estimated $2.4 billion in worldwide sales this year for prescription drugs for male sexual dysfunction, according to market research firm Decision Resources.

P&G is one of about 10 drug companies seeking to create parity in the sexual dysfunction arena by developing drugs for women. None of the other products, ranging from creams to a hormone sprayed on the skin, is expected to reach the market before 2006.

Decision Resources estimates that the global market for female sexual dysfunction could grow to $1 billion in the next decade. But some experts wonder if Intrinsa's approval might be delayed in the wake of Merck & Co.'s withdrawal of Vioxx (search).

The FDA has been criticized for its role in keeping the pain reliever on the market despite early warning signs of potentially lethal side effects, and many expect the agency to adopt a more cautious approach to drug approvals. In addition, a huge 2002 study showed that women taking an estrogen-progestin hormone pill to ease their menopause symptoms face an increased risk for breast cancer and other problems. Testosterone is a hormone, and the study has led doctors to be more wary of prescribing it.

Those concerns could lead the FDA panel to postpone recommending Intrinsa's approval until more data is available. P&G's submission is based on six months of efficacy data and 12 months of safety studies.

"It is hotly debated whether the lack of long-term data will mean waiting another 6 to 12 months for approval," said Dr. Andre Guay, director for sexual function at the Lehay Clinic in Burlington, Mass.

Intrinsa is part of Cincinnati-based P&G's plan to introduce more health care products, especially pharmaceuticals, which have higher margins than its consumer products, according to Douglas Christopher, an analyst with Crowell, Weedon & Co. in Los Angeles.

P&G is best known for its Tide laundry detergent, Crest toothpaste and Pampers diapers but the company does sell seven drugs including osteoporosis treatment Actonel. After-tax margins on consumer products are in the 13 percent range while they reach 30 percent on prescription drugs, Christopher said.

Millions of women have difficulties with libido, arousal or orgasm. But the search for a female equivalent to Viagra worries some who say that a women's sexual response is more emotionally and psychologically driven than a man's so it is less likely to respond to medication.

"Psychological variables like stress, cultural inhibitions, religious inhibitions and relationship issues affect women's sexuality," said Dr. Leonore Tiefer, an associate professor of psychiatry at the New York University School of Medicine, who counsels people with sexual difficulties. "The problem is they are more difficult to assess and not amenable to a pill."

P&G is seeking approval for Intrinsa in women who have had their ovaries removed. Ovaries are a key producer of testosterone, which helps drive sexual desire. (Men produce testosterone in the testicles.) There are about 10 million women who have had their ovaries removed and one in five could suffer from a low sex drive, according to P&G.

Doctors have been prescribing testosterone products approved for men to women with low sexual desire for years. However, the testosterone women receive is either created in pharmacists' office in forms such as creams or reduced dosages of gels designed for men. Doctors have worried about the consistency of such products.

Intrinsa, which P&G licensed from Watson Pharmaceuticals Inc. in 1997, works by releasing over time testosterone through the skin in an amount a women would have produced before menopause. The dose is much lower than the amount prescribed for men.

P&G studied a total of 1,095 surgically menopausal women in two trials where the patients wore the egg sized patch, which must be changed twice a week. In one study, the women using the patch reported a 74 percent increase in satisfying sexual encounters, averaging to 4.92 over a four-week period. The placebo group reported a 35 percent increase to 3.8 encounters.

The company is also testing the drug on naturally menopausal women who lose testosterone as they age. About 30 million women have gone through natural menopause and one in 10 may have a lackluster libido.

But doctors would be able to prescribe drugs as they see fit. So some believe Intrinsa's sales are likely to transcend its relatively narrow initial intended market. Analysts' sales estimates for the product range from $400 million to $1 billion.

"I can see anyone who thinks they should be more sexy or whose partner wants them to be more sexy asking for this," said Stephanie Sanders, assistant director of the Kinsey Institute for Research in Sex, Gender and Reproduction at Indiana University.

P&G spokeswoman Mary Johnson wouldn't comment on Intrinsa's price or potential market size. She did say the company plans a marketing campaign for doctors and women to discuss its appropriate use.

"We know this drug isn't for everyone," said Johnson. "We don't want people to be disappointed."

Johnson said P&G's relationships with gynecologists and primary care doctors who prescribe Actonel should help Intrinsa's launch. "We have a deep understanding of menopausal women," Johnson said.

Psychiatry professor Tiefer hopes doctors would be more cautious in prescribing Intrinsa because of the hormone study, but she worries that those concerns will be overwhelmed by what she expects to be a marketing monsoon by P&G.

"This is a company interested in building another billion dollar brand," she said.

Sheryl Kingsberg, an investigator for P&G, disputes that thinking. She said that unlike Viagra and its rivals, which are taken episodically and can be used to enhance individual encounters, wearing the patch is a long-term commitment. Kingsberg said the 2002 study has made women suspect about hormones so only those who will truly benefit will use it.

"Women will be smart about taking hormones," Kingsberg said. "I have faith in women."