The FDA said it won't approve the oral multiple sclerosis drug cladribine without more data on its safety and benefit-risk balance.
Merck KGaA, the drug's German manufacturer, said it has received a complete response letter from the FDA indicating that the company would have to provide additional analyses of its clinical trials data or conduct new studies to satisfy its concerns.
However, the company said it was encouraged that the letter confirmed that the existing trial data were adequate to support the drug's efficacy in reducing MS exacerbations and progression.
Cladribine is currently marketed as a chemotherapy drug for certain leukemias and lymphomas. A series of studies has shown that it inhibits activity and proliferation of lymphocytes involved in MS, prompting Merck KGaA to seek approval for cladribine as a treatment for the autoimmune disease.
The FDA decision is the latest in a string of setbacks for the company.
Its first submission was rejected out of hand by the FDA in late 2009, prompting Merck KGaA to refile last June.
Then, in September, an advisory committee within the European Union's drug regulatory agency voted against approving the drug. The company later withdrew its European application.
Merck KGaA said it planned to meet with FDA officials "to clarify next steps and to identify whether data from completed and ongoing clinical studies can address the agency's questions."