The chances of AstraZeneca's new infant lung drug motavizumab making it to the market have taken another hit after regulators asked yet again for more data.

The US Food and Drug Administration has issued a second complete response letter on the monoclonal antibody which the Anglo-Swedish drugmaker is looking to get approved for prevent serious respiratory syncytial virus disease. Specifically, the agency has requested evidence from "an additional clinical trial that supports a satisfactory risk/benefit profile in the population(s) for which the prophylaxis indication is being requested".

In June, the FDA’s Antiviral Drugs Advisory Committee voted 14 to 3 to recommend that motavizumab, developed by AstraZeneca's MedImmune biologics unit, should not be approved, claiming that the data provided merely shows that motavizumab is only as effective in reducing RSV hospitalisations as the company’s older treatment Synagis (palivizumab). The latter treatment, which is expected to lose patent protection in 2015, had sales last year of around $1.1 billion in 2009.

AstraZeneca says it "continues to believe in the clinical benefit of motavizumab, and it will conduct a complete review of the CRL". The company added that following "ongoing constructive dialogue with the FDA", it will then "make a decision regarding next steps in due course".

Things do not look great, however, and AstraZeneca went on to note that it holds "intangible assets of $445 million relating specifically to motavizumab". These may be "subject to impairment following completion of the group’s analysis of the CRL", but the firm noted that this would be excluded from core profits and, as such, the company’s earnings per share guidance for 2010 remains unchanged at $6.35-$6.65.