As expected, regulators in the USA have rejected Novartis heart failure drug serelaxin, a treatment that has breakthrough therapy designation.

The US Food and Drug Administration has issued a complete response letter regarding the Biologics License Application for serelaxin for the treatment of acute heart failure, stating that further evidence on its efficacy is required. The rejection comes a couple of months after the agency's Cardiovascular and Renal Drugs Advisory Committee voted unanimously against approval.

The submission for the drug, which is a relaxin receptor agonist, included one Phase III trial, the design of which was criticised by FDA staffers. Now Novartis is conducting a second late-stage trial which will enroll over 6,300 patients to expand the data, though this is unlikely to report for a couple of years.

Nevertheless, Novartis remains upbeat about the prospects for serelaxin and Tim Wright, head of pharmaceutical development, said "we continue to believe [it] has the potential to be an important treatment for AHF". He added that Novartis has been "encouraged by feedback from FDA advisory committee members noting the data are intriguing".

The FDA granted breakthrough status to serelaxin last June but the complete response letter highlights the fact that being on that particular fast-track programme does not necessarily make the approval pathway any easier. The European Medicines Agency's Committee for Human Medicinal Products also declined to back the drug in January.