Merck KGaA’s bid to win the battle to be the first firm with an approved multiple sclerosis pill on the market has suffered a blow after regulators in the USA rejected its filing for cladribine.

The US Food and Drug Administration has issued a ‘refuse to file’ letter for Merck's New Drug Application for cladribine, which the firm hopes will be would be the first oral treatment for relapsing forms of MS. The agency issues such letters if, after a preliminary assessment, it believes the NDA is not sufficiently complete to permit a substantive review.

Elmar Schnee, head of the German firm’s Merck Serono unit, said the company will work closely with the agency to “fully understand FDA's concerns and define a path forward for a successful resubmission of this application at the earliest point”. Merck spokesman Gangolf Schrimpf, who declined to give any details about the content of the letter, told PharmaTimes World News that the company has 30 days to request a meeting with the FDA, which then has an additional 30 days to respond.

Merck submitted its cladribine file to the FDA at the end of September, two months after a filing in Europe. It had hoped to steal a march on other investigational oral compounds, notably Novartis' FTY720 (fingolimod), which is expected to be filed in the USA and Europe before 2009 is out.

News of the FDA’s negative letter is the second piece of bad news Merck KGaA has had from regulators in the last week or so. Recently, the European Medicines Agency’s Committee for Medicinal Products for Human Use adopted a negative opinion that was originally issued in July for the use of Erbitux (cetuximab) in combination with platinum-based chemotherapy for the treatment of patients with metastatic non-small cell lung cancer.

Merck's shares were hit fairly hard by the cladribine news, falling just over 4% to 62.81 euros.