Sprout Pharmaceuticals has pulled off the improbable task of getting its female sexual dysfunction drug flibanserin approved in the US. But though the drug has been dubbed the “female Viagra”, it looks unlikely to live up to Pfizer’s blue pill.
For a start the impact of Addyi, as it is branded, seems small: the pivotal studies showed an average increase in the number of satisfying sexual events of just 0.5 per month. There are also the worrying side-effects of low blood pressure and fainting, which increased when women also drank alcohol or took other medications, and mean that the drug will carry a boxed warning.
The FDA has also told Sprout to conduct three more studies to investigate the interaction between Addyi and alcohol.
Underneath all this there are the inherent problems with measuring female sexuality and the mechanism of action of Addyi, a serotonin 1A receptor agonist and a serotonin 2A receptor antagonist. While the likes of Viagra do not increase desire and just treat the mechanics of erectile dysfunction, Addyi goes to work in the brain – and even the FDA admits that the mechanism by which the drug improves sexual desire is not known.
This makes Addyi’s action more similar to antidepressants – in fact, it was originally developed for this use but failed to show efficacy. For Sprout's part, Cindy Whitehead, chief executive, did acknowledge these differences during a conference call to discuss the approval, and played down the "female Viagra" tag.
So why has the FDA approved the drug now, after rejecting it twice? There is no doubt that privately held Sprout has been helped by the efforts of advocacy group Even the Score, which the company helped set up and is campaigning for women’s sexual health quality. The organisation points out that there are already 26 FDA-approved treatment options for men’s sexual dysfunction and called for approval of Addyi in the name of equality.
In spite of these seemingly successful lobbying efforts, Ms Whitehead said on the call that the approval was "purely based on science".
However, not everyone believes that the decision is a step forward for women’s rights, including a coalition led by the National Women’s Health Network, which supported the FDA’s previous rejections on safety and efficacy grounds.
Women suffering from hypoactive sexual desire disorder (HSDD) will argue that at least they now have an option, where none was available before. It is worth noting that the Even the Score campaign collected over 60,000 signatures calling for Addyi’s approval, and Sprout estimates that 10% of women have HSDD, so there does seem to be an unmet need.
Whether Addyi addresses that need will soon become apparent as sales figures begin to come in.