Women with low libido in the US will have to wait even longer for approval of the first ever treatment for the condition after regulators requested more data on the forerunner flibanserin, delaying its submission until later this year.

The US Food and Drug Administration has asked manufacturer Sprout Pharmaceuticals for data on how flibanserin interacts with other medicines and also how it affects driving ability, after around 10% of patients experienced sleepiness while on the drug.

This means that the firm will have to carry out two additional Phase I drug interaction studies and a Phase I driving simulator study, involving around 25-50 healthy volunteers in each, before it can resubmit flibanserin as a once-daily treatment for Hypoactive Sexual Desire Disorder (HSDD) in premenopausal women.

The good news, says Sprout, is that additional efficacy studies have not been requested by the regulator, which must come as a great relief given that, back in 2010, an FDA advisory committee voted 10-1 that flibanserin is not effective in increasing female libido.

The FDA's request for additional data and suggested pathway to potential approval comes via a formal dispute resolution filed by Sprout in December, after receiving yet another rejection for the drug, on the basis that the agency was misunderstanding efficacy measures.

Sprout, which bought flibanserin from Boehringer Ingelheim after it was rejected by the FDA in 2011, said it will resubmit the New Drug Application (NDA) by the third quarter.