FDA gives female libido drug another shot at approval after more studies

Sprout Pharmaceuticals is getting a second chance with its hopes of marketing a female Viagra analog, as the FDA has given it a new pathway to approval and recommended some additional studies, the company said.

According to Sprout, the agency will reconsider the once-rejected flibanserin, suggesting the company conduct two Phase I drug-interaction studies and run a third trial to determine whether the treatment impairs patients' driving ability. Sprout figures it can get those studies done and resubmit flibanserin by the third quarter.

What remains unclear is how some new safety data will improve the odds of a drug rejected for its efficacy. Flibanserin, previously abandoned by Boehringer Ingelheim, failed to impress regulators in its first submission last year, as the FDA was unmoved by its "modest" effect on hypoactive sexual desire disorder in premenopausal women. The agency's response to Sprout's resultant appeal indicates that regulators are ready to listen again, but there's no indication the FDA has changed its standards for what makes an effective treatment.

In flibanserin's pivotal results, women on the drug averaged 2.5 satisfying instances over 28 days, compared to 1.5 for those on placebo. Despite its inability to please the FDA, Sprout contends that that's a clinically meaningful difference, because, as COO Cindy Whitehead said in December, "flibanserin does not cause hypersexuality, but, by that definition, 'modest' would be what we're aiming for."

And the pressure to approve flibanserin isn't coming from just the drug's sponsor. As Reuters reports, last month, representatives from 8 women's advocacy groups met with CDER Director Janet Woodcock to lobby for the drug, pointing out that the agency has approved 24 treatments for male sexual dysfunction and not one for women. That disparity is the result of inconsistent standards and murky endpoints for efficacy, according to the groups, and flibanserin's review could be an "inflection point" for the agency.

While that may be true, the semiotic differences involved in assessing male and female libido drugs don't make the FDA's task any easier. Erectile dysfunction is, at its core, a physiological problem, making the definition of clinical endpoints fairly straightforward. What drugs like flibanserin intend to treat has a much larger psychological component, meaning the FDA must consider subjective endpoints like "satisfying sexual encounters" in its deliberations, which makes for a more nebulous process.

But Sprout is resolute that its drug can make a meaningful difference in the lives of its potential patients, and the FDA's offering of a second chance is plenty cause for optimism, Whitehead said.

"With data in over 11,000 patients to date, we are confident that further supporting the predictable risk/benefit profile of flibanserin will result in women having the first ever treatment for the most common form of female sexual dysfunction," she said in a statement.

- read Sprout's announcement
- here's the Reuters story