Cubist Pharmaceuticals is facing a delay in the USA before it can win approval for its antibiotic Cubicin in a new indication, the treatment of a potentially life-threatening complication that can occur in patients infected with Staphylococcus aureus.

Cubicin is already approved in the USA as a treatment for complicated skin and skin structure infections, but the new labelling – covering S aureus infections of the blood and a life threatening infection of the heart called infective endocarditis, would provide further momentum to a product that saw sales double last year to $114 million.

In a letter, the US Food and Drug Administration (FDA) said that Cubist's application is approvable, subject to the FDA and the company reaching an agreement on labelling for the product. An FDA advisory committee gave its unanimous support to the blood infection labelling earlier this month, but was split on the infective endocarditis data, with some panellists suggesting that as efficacy had not been conclusively shown, patients should be carefully monitored to make sure treatment was working.

Cubist said in a statement that "we are disappointed that we have not been able to reach agreement on the label, but we plan to commence a process with the FDA next week to resolve the label negotiations within 60 days."

Cubicin was launched earlier this month for SSTI in its first European markets, the UK and the Netherlands, by Cubist’s partner Chiron.