The US Food and Drug Administration's non-member expert panel is to vote Friday on the efficacy and safety of flibanserin, touted for sometime as the 'female viagra.' But prospects look bleak.
For, in the briefings prepared for the committee, the regulators said the response rate of flibanserin was "not compelling," and the drug yielded only slight improvements for treating hypoactive sexual desire disorder or HSDD.
Flibanserin, made by Boehringer Ingelheim, is under evaluation for the treatment of low sex drive in women who have not yet reached menopause.
Flibanserin, which was originally studied as a possible antidepressant, is an oral pill designed to be taken once daily.
Studies of the product showed it didn't work well as an antidepressant but showed that it didn't appear to damp sexual desire as some antidepressants do. The FDA said antidepressant studies showed flibanserin was superior to placebo and a comparator drug with respect to a question about "how strong is your sex drive" on a sexual-experience scale.
The flibanserin data involved about 2,400 women treated with either flibanserin or a placebo for about six months. The agency said the two groups showed an increase in their number of sexually "satisfying" events but didn't show a boost in a sexual-desire score. The "overall response rate...is not particularly compelling," the FDA said, even though many of the differences in response rates between the two groups were statistically significant.
The FDA said common side effects seen with flibanserin are dizziness and nausea, and noted that tolerability of the product was "moderate." About 15% of women on flibanserin stopped taking the drug before the studies ended because of a side effect compared with 6.8% of women in the placebo group.
The agency said tolerability of flibanserin was "adversely affected" when taken with alcohol or given with other commonly used drugs such as antidepressants and hormonal contraceptives. Women with a history of depression and other psychiatric problems weren't included in the clinical studies. "It is not clear if labeling alone will be sufficient to alert women to the numerous drug interactions that exist with flibanserin," the FDA said.
Boehringer's report for the advisory committee acknowledges that desire was only significantly enhanced in one of three trials of the drug, but notes "positive trends" in the other two. Those taking the drug also consistently scored better on the 'Female Sexual Function Index - Desire Items', an assessment of sexual desire over 28 days, leading Boehringer to conclude that "flibanserin is more consistently effective in increasing women's global experience of desire than in increasing the intensity of their acute episodes of desire". (The FDA, however, noted that the sexual function index may be susceptible to 'recall bias'.)
A spokesperson for Germany-based Boehringer Ingelheim, the manufacturer of flibanserin, says the company is still optimistic.
"We remain confident that our data demonstrates Flibanserin is safe and effective in balancing the chemicals in the brain linked to sexual desire," says Peter Piliero, executive director of U.S. medical affairs for Boehringer Ingelheim. "We have conducted a robust program showing that flibanserin shows improvement increasing satisfying sexual events, in improving sexual desire and lowering distress," he adds.
Low sex drive is said to affect nearly 40 percent of women in the United States, according to some estimates. Currently, there is no medication approved to treat HSDD in women.
In 2004, an FDA panel unanimously voted down a Procter & Gamble Co. testosterone patch that aimed to boost sexual desire in women. The panel said the benefit of slightly increasing the number of sexually "satisfying" events wasn't significant enough to outweigh unknown safety risks.
There is also the as yet unresolved question of what "female sexual dysfunction" really is, and whether medications are the best way to address it. NYU psychiatry professor Leonore Tiefer has been a perennial critic of FSD as a disease category, calling it in this PLoS Medicine essay "a textbook case of disease mongering." (The recent documentary "Orgasm Inc." is by a filmmaker who worked for a drug company editing erotic videos for use in its FSD drug trials.)
Tiefer will speak against the drug's approval at Friday's hearing, "arguing it offers meager benefits for women with unknown long-term risks," AP reports. As a urologist tells the news agency, the many different aspects of women's sexual difficulties may simply make them too complex to be addressed by drugs.
Boehringer Ingelheim, meantime, says hypoactive sexual desire "is not an adaptive response to a poor relationship," nor the result of stress or depression, but is a distinct condition that causes women distress.