If sexual statistics are to be believed, roughly 43 percent of American women suffer from some form of female sexual dysfunction.

But pharmaceutical companies to date have only commercialized male sex drugs.

Pfizer’s (NYSE: PFE) Viagra in 1998 famously became the first erectile dysfunction drug targeting men looking to revive their sex lives. It spurred other firms to develop libido-enhancing drugs for a market that now tops $5 billion a year. Meanwhile women are still waiting for just one drug that could become a “female Viagra.”

Here’s another figure: $20 million.

That’s how much Raleigh startup Sprout Pharmaceuticals has raised in private investment to develop a drug that increases sexual desire in women.

“There’s a lot of pent up demand because there have been a lot of drugs for men over the last decade,” said Cynthia Whitehead, Sprout’s chief commercial officer. “It will be exciting to be the first one for women.”

Sprout is working toward Food and Drug Administration approval for flibanserin, a compound developed to treat hypoactive sexual desire disorder – a form of female sexual dysfunction that essentially means low sexual desire. The company acquired the compound late last year from German pharmaceutical giant Boehringer Ingelheim.

No financial terms were disclosed in the deal, which gave Sprout global rights to flibanserin.

Sprout is treading where other pharmas have failed.

Boehringer sought FDA approval for flibanserin in 2010. But the FDA declined to approve it amid questions about the compound’s efficacy and safety.

Last December, roughly at the time when Sprout acquired flibanserin, Illinois drug developer BioSante Pharmaceuticals (Nasdaq: BPAX) disclosed its hormone gel Libigel failed to work better than a placebo in phase 3 clinical trials. BioSante last month said it would try again with a pair of phase 3 studies.

Payoff Could Be Huge

San Diego-based Apricus Biosciences (Nasdaq: APRI) has taken its female sexual arousal disorder compound Femprox as far as one phase 3 clinical trial. But Apricus doesn’t plan on additional studies until it lands a co-development partner.

The potential payoff – to BioSante, Sprout or Apricus – is huge.

BioSante has said 43 percent of women between 18 and 59 experience some form of female sexual dysfunction, citing figures from the Journal of the American Medical Association. The company projects the female sexual dysfunction market could top $2 billion a year.

The first company to win FDA approval would likely dominate the market, much the way Pfizer’s Viagra did more than a decade ago.

Whitehead says Sprout aims to resubmit a flibanserin drug application in early 2013. Boehringer originally studied the compound as a depression treatment. It targets the brain. Whitehead said that this different mechanism of action distinguishes it from failed hormonal sex drugs.

But like BioSante, Sprout must also address placebo performance issues that doomed flibanserin’s first application. The FDA also raised concerns about potential adverse drug interactions. Clinical trials studied healthy women who took few other medications and regulators were unsure whether noting those risks on a label would be enough to alert women “to the numerous drug interactions that exist with flibanserin.”

Sprout believes flibanserin, which Boehringer studied in more than 11,000 women, can secure FDA approval without additional clinical studies. Without going into detail, Whitehead said “flawed metrics” in looking at the data led the FDA to deny flibanserin approval. “It will be a review issue,” she said. “We feel we have all of the data we need.”

Angel Investors Provide Funding

Sprout has the financial backing of 59 angel investors who participated in the $20 million securities offering. It’s the same investor group that backed Slate Pharmaceuticals, the Raleigh company that spun out Sprout last year.

Slate, which addressed male sexual dysfunction with testosterone product Testopel, was acquired by private Chicago-area drug company Actient Pharmaceuticals in late 2011. Terms of that deal weren’t disclosed either.

Whitehead said the new funding will support Sprout’s operations and growth including hires of scientists and regulatory personnel as the company prepares its new drug application.

In the meantime, Whitehead said Sprout is trying to keep a low profile and she declined to even say how many people work for the company, though she acknowledged that the management team and some other staffers came from Slate.

If Sprout turn flibanserin into the first female sexual dysfunction drug, it will be hard to keep things under wraps for long.

(Note: Capitol Broadcasting is an investor in the company.)