Forest Laboratories says it has pulled out of a collaboration with fellow US firm Replidyne to develop an antibiotic which was rejected by the US Food and Drug Administration last October.

The two firms linked up last February to develop faropenem medoxomil but received a jolt when the FDA issued a non-approvable letter for all four uses for which Replidyne had sought the green light – acute bacterial sinusitis, community-acquired pneumonia, acute exacerbation of chronic bronchitis and uncomplicated skin and skin structure infections.

Explaining his firm’s decision to terminate the deal, Forest chief executive Howard Solomon said the agency's non-approvable letter “clearly raises regulatory uncertainty. We have carefully reviewed all the existing data and the FDA's pronouncements and have determined that we should not continue further development of the faropenem programme."

Replidyne, which will re-acquire all US adult and pediatric rights previously granted to Forest, does not share Mr Solomon’s pessimism and chief executive Kenneth Collins said "we remain confident in the viability of faropenem” as it could offer important advantages over current therapy. “Though the regulatory requirements for the approval of antibiotics have changed, we believe that faropenem can meet these new standards and are we working closely with the FDA to define a regulatory pathway for faropenem approval," he concluded.