UCB has suffered a major blow with the news that US regulators have asked for more safety data on the Belgian drugmaker’s anti-tumour necrosis factor agent Cimzia as a treatment for rheumatoid arthritis.

The US Food and Drug Administration has issued a complete response letter relating to the Biologics License Application for Cimzia (certolizumab pegol) relating to the aforementioned indication. As a prerequisite for approval, the agency has requested a new safety update with all clinical data including new information generated since the filing of the BLA.

The file, which was accepted for review in February last year, was based on a clinical programme which included more than 2,300 patients, representing more than 4,000 patient years of experience, UCB said. The company noted that it has been invited to a meeting by the FDA, which is expected to take place within the next month, “to define the path forward”.

UCB’s chief medical officer Iris Loew-Friedrich said the firm is “confident and committed to making Cimzia available to people living with moderate to severe rheumatoid arthritis and other inflammatory conditions as soon as possible”. She added that UCB “will work diligently with the FDA to fulfill their request”.

Cimzia was approved for Crohn’s disease in the USA in April but the RA indication would be much more lucrative and help UCB plug the gap in sales resulting from the loss of patent protection on its biggest earners – the allergy drug Zyrtec (cetirizine) and the antiepileptic Keppra (levetiracetam).

Analysts at Morgan Stanley believe that the FDA’s request is not too serious, saying that UCB could get a final decision from the agency in the second half of 2009 if it supplies the additional information requested in the next three months or so. Investors seem a bit more concerned and at 9.10 UK time, the firm’s share price was down almost 7% to 24.02 euros.