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Company Resubmits Women’s Libido Pill to FDA

Agency petitioned to reconsider twice-rejected flibanserin

The makers of a twice-rejected pill designed to boost sexual desire in women are hoping a year-long lobbying push by politicians, women’s groups, and consumer advocates will move their much-debated drug onto the market.

The ongoing saga of Sprout Pharmaceutical’s female libido drug illustrates the complicated politics and unresolved science surrounding women’s sexuality.

For decades, drug-makers have tried unsuccessfully to develop a female equivalent to Viagra (sildenafil, Pfizer), the blockbuster drug that treats men’s erectile dysfunction by increasing blood flow. But disorders of women’s sexual desire have proven resistant to drugs that act on blood flow, hormones, and other simple biological functions.

Supporters of Sprout’s drug say women’s sexual disorders have been overlooked for too long by regulators at the FDA. But critics argue that women’s sexuality is too complex to be addressed by a single pill.

Sprout’s drug, flibanserin, is the first attempt to increase libido by acting on brain chemicals linked to appetite and mood.

Flibanserin is a multifunctional serotonin agonist antagonist (MSAA) and, if approved, would be the first postsynaptic 5-hydroxytryptamine (5HT1A) receptor agonist and 5HT2A receptor antagonist available for the treatment of premenopausal women with hypoactive sexual desire disorder (HSDD). According to Sprout, it is believed that flibanserin helps restore prefrontal cortex control over the brain’s motivation and rewards structures, thereby allowing sexual desire to manifest. This is thought to be accomplished by the rebalancing of neurotransmitters that influence sexual desire. Specifically, flibanserin increases dopamine and norepinephrine (both responsible for sexual excitement) while transiently decreasing serotonin (responsible for sexual satiety/inhibition) in the brain’s prefrontal cortex. This is likely accomplished by reduced glutamate transmission, Sprout says.

But the FDA has already rejected the drug twice because of lackluster effectiveness and adverse effects, including fatigue, dizziness, and nausea.

In an effort to break the regulatory logjam, groups sponsored by Sprout and other drug-makers have begun publicizing the lack of a “female Viagra” as a women’s rights issue. Drug-makers often cite a 1999 survey published in JAMA, which found that 43% of U.S. women had some type of sexual dysfunction.

The FDA first rejected flibanserin in 2010 after an advisory panel unanimously voted against the drug, saying its benefits did not outweigh its risks. The drug’s initial developer, Boehringer Ingelheim, abandoned work on the treatment in 2011 and sold it to Sprout, a startup company in Raleigh, North Carolina.

Sprout resubmitted the drug with additional effectiveness and safety data, but the FDA again rejected it in October 2013. After Sprout filed a formal dispute over the decision, FDA regulators requested the driving study and other details on the drug’s interactions with other medications.

As Sprout gathered those data, the company also enlisted support from allies in Washington. Last January four members of Congress, including Rep. Debbie Wasserman Schultz, D-Florida, sent a letter to the FDA, urging a careful reassessment of the drug and lamenting the lack of drug options for low female libido.

The talking point about the imbalance of drugs for men versus women was picked up by a coalition of seven women’s and consumer health groups, who met with the FDA early last year.

Then, last October, the FDA held a 2-day meeting at its headquarters to obtain public input on the problem of female sexual dysfunction and the challenge of developing treatments.

Because so many factors affect female sexual appetite, doctors must rule out a number of other possible causes before diagnosing HSDD, including relationship problems, hormone disorders, depression, and mood issues caused by other drugs, such as sleeping aids and pain medications.

Sources: Medical Xpress; February 17, 2105; and Sprout Pharmaceuticals; February 17, 2015.


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