ENEVA, March 2, 2011 /PRNewswire/ -- Merck Serono, a division of Merck KGaA, Darmstadt, Germany, announced today that it received a complete response letter (CRL) from the U.S. Food and Drug Administration (FDA) on the new drug application (NDA) for Cladribine Tablets, Merck Serono's proprietary investigational oral formulation of cladribine, as a therapy for relapsing-remitting multiple sclerosis (MS).

A complete response letter is issued by the FDA when the Agency's review of a file is complete and the application cannot be approved in its present form. In the complete response letter, the FDA concluded that substantial evidence of Cladribine Tablets' effectiveness was provided by the CLARITY1 study. However, the FDA has requested the Company provide an improved understanding of safety risks and the overall benefit-risk profile either through additional analyses or by additional studies. Merck Serono intends to request an end-of-review meeting with the FDA to clarify next steps and