The US Food and Drug Administration has rejected Gilead Science’s inhaled cystic fibrosis drug aztreonam lysine on the grounds an additional clinical study is required.

The agency sent the California-based biopharmaceutical company a complete response letter for its New Drug Application for aztreonam lysine, an inhaled antibiotic to treat Pseudomonas aeruginosa infections in patients with cystic fibrosis.

The company said no particular safety concerns were raised about the drug, but further information on why the FDA had requested another trial was not disclosed.

According to a statement released by Gilead, the company looked to be trying to avoid an extra costly trial despite the FDA’s request, saying Gilead “will continue its dialogue with the FDA to determine whether further analyses of existing data could lead to approval”.

Gilead Chairman and Chief executive John Martin said: “Cystic Fibrosis-related pseudomonal infections represent an area of significant and urgent unmet medical need. Our goal is to work with the FDA to deliver this product to the medical community and to people living with cystic fibrosis as quickly as possible.”

Gilead submitted the NDA for the drug in November last year. The need to run a further clinical trial would set back the approval of the drug a possible 18 months.

The drug is currently under review by regulatory agencies in Europe.