Sanofi has received a refuse-to-file letter from the US Food and Drug Administration regarding the filing of its new Bayer-partnered multiple sclerosis treatment Lemtrada.

The regulator has held "collaborative consolations" with the French drug giant's Genzyme unit regarding its supplemental Biologics License Application for Lemtrada (alemtuzumab) and the FDA has requested that the company "modify the presentation of the data sets to enable the agency to better navigate the application". However, the agency has not requested additional data or further studies.

Genzyme says it will work with the FDA over the coming weeks to resubmit the application as soon as possible. The unit's chief executive David Meeker said the firm has had "constructive dialogue with the FDA, and we are very confident in our ability to address the agency’s request and resubmit rapidly”.

Sanofi submitted the sBLA in June, the same time that a marketing authorisation application was made to the European Medicines Agency. The latter has accepted the filing and the review process in Europe is underway.

The refuse-to-file letter comes a week after Sanofi said it is pulling an already-approved different-dose form of alemtuzumab, Campath/MabCampath for B-cell chronic lymphocytic leukaemia, from markets on both sides of the Atlantic in order to concentrate on the compound in MS.