Sanofi's Genzyme subsidiary has been sent a refuse-to-file letter from the US Food and Drug Administration (FDA) for Lemtrada, its new multiple sclerosis (MS) therapy partnered with Bayer.
The US agency has asked the pharma company to change the way the data is presented in the marketing dossier in order to help it to "better navigate the application", said Sanofi in a statement, stressing that no additional data or studies have been requested.
Lemtrada (alemtuzumab) was submitted for approval in June in both the US and EU as a treatment for the treatment of relapsing MS, and the European Medicines Agency (EMA) has already accepted the filing and started its review process.
Genzyme's chief executive David Meeker said that the company was working with the FDA to resubmit the marketing application and has had "constructive dialogue" with the agency.
"We are very confident in our ability to address the agency's request and resubmit rapidly," he added, although the resubmission is likely to delay a launch by months.
Sanofi had been targeting a late-2012 or early 2013 launch for Lemtrada, assuming it was able to secure priority review status for the application with the FDA, with analysts predicting sales of $500m or more within five years of its introduction.
Lemtrada is a key pipeline product for Sanofi as it copes with the loss of patent protection on multibillion-selling antiplatelet drug Plavix (clopidogrel).
The new drug has demonstrated superior efficacy in clinical trials to Merck Serono's Rebif (interferon beta-1a), a standard treatment for MS, achieving a 49 per cent reduction in relapse rates compared to its rival. It also has favourable dosing, requiring administration just once a year, compared to three times a week for Rebif.
News of the knockback in the US comes just a few days after Sanofi took its Campath/MabCampath formulation of alemtuzumab off the market - used to treat a rare form of leukaemia - for fear of cannibalising sales of Lemtrada and to allow it to price the new drug at a level closer to rival MS drugs such as Novartis' Gilenya (fingolimod).