The 15-year search for a
pill that boosts sexual desire in women has hit another roadblock, raising
questions about the future of efforts to develop a female equivalent to Viagra.
Sprout Pharmaceuticals said
Wednesday it has reached an impasse with the Food and Drug Administration over
its drug, flibanserin. The daily pill is designed to increase libido in women
by acting on brain chemicals linked to mood and appetite.
The FDA questions whether
the drug's benefits outweigh its risks, considering its "modest"
effectiveness and side effects including fatigue, dizziness and nausea.
Sprout said it is appealing
an October letter from the FDA that denied approval and asked for more
information. But chances for approval appear slim: Of the 17 appeals FDA
considered last year, 14 were denied, according to government figures.
The agency's letter is the
latest challenge for companies working to develop therapies for women who
report stress due to lack of libido. It's a market drug makers have been trying
to tap since the success of Viagra, an erectile-dysfunction drug that was
developed in the late 1990s to increase blood flow to the genitals.
But unlike sexual problems
in men, most of women's sexual issues are psychological, not physical. As a
result, there are a number of alternate causes doctors must consider before
diagnosing female sexual desire disorders, including relationship problems,
hormone disorders, depression and mood issues caused by other medications.
Likewise, other factors must be considered when treating it.
Experts say that developing
drugs for female sexual dysfunction is so difficult because of how little we
understand the underlying causes.
is a really easy thing to measure," says Emory University researcher Kim
Wallen. "Motivation is a hard thing to measure and, quite honestly, we
don't know enough about what creates sexual motivation to manipulate it."
And Dr Virginia Sadock, a
psychiatrist, says the idea that a single pill can restore female libido
oversimplifies the problem. Even if the FDA eventually approves a drug for
female sexual dysfunction, she says it will likely be used with non-drug
techniques to reduce stress and improve self-image.
"A pill just doesn't
take care of it," says Sadock, who teaches human sexuality at New York
University's School of Medicine. "You may take a statin drug to control
your cholesterol, great. But you should also exercise and you should also watch
Drug makers have made
several unsuccessful attempts at tweaking their approach to boosting female
libido over the years. Initially, Pfizer tested Viagra on women, hoping that
the drug's ability to increase blood flow to genitals would increase sex drive
When that didn't work, drug
makers turned to hormones, including the male hormone testosterone. In 2004, an
FDA panel rejected Procter & Gamble's testosterone patch, Intrinsa, due to
questions about its long-term safety – despite evidence of effectiveness.
Sprout's flibanserin is the
first drug to approach the problem through brain chemistry. Sprout acquired
flibanserin from Boehringer Ingelheim in 2011, after the German drug maker
abandoned development of the pill following an FDA rejection letter.
Researchers believe the
drug works by boosting dopamine – a brain transmitter associated with appetite – while lowering serotonin – another transmitter linked with feelings of
satiation. Studies of the drug show that it boosts sexual desire, reduces
stress and increases "sexually satisfying events", reported by women
with hypoactive sexual desire disorder, or a lack of sexual appetite that
The FDA has twice rejected
flibanserin since 2010. A key issue for the agency is that women taking the
drug reported only 1.7 more satisfying sexual experiences per month than women
Sprout executives argue
that number is statistically significant and warrants approval for their
product, considering there are no other drugs approved for the condition.
"We've now got 24
drugs for men for either testosterone replacement or erectile
dysfunction," says Cindy Whitehead, Sprout's chief operating officer.
"Yet there are zero drugs for the most common form of sexual dysfunction
The FDA, which does not
comment on drugs under appeal, is expected to make a decision on Sprout's
appeal in the first quarter of next year.