Merck MS drug denied FDA approval

The US Food and Drug Administration (FDA) has declined to approve Merck KGaA's marketing application for the company's proprietary investigational oral formulation of cladribine as a treatment for relapsing-remitting multiple sclerosis (MS).

In a complete response letter, the agency said the application could not be approved until the company provided "an improved understanding of safety risks and the overall benefit-risk profile either through additional analyses or by additional studies," according to Merck.

The FDA did acknowledge that substantial evidence of effectiveness was provided by Merck's CLARITY1 study, a two-year phase III placebo-controlled trial that evaluated cladribine tablets as a monotherapy in patients with relapsing-remitting MS.

Merck said it will request an end-of-review meeting with the FDA to determine whether new studies will be needed or whether data from completed and currently ongoing clinical studies will be sufficient to address the agency's concerns.

The company said it remains committed to completing the ongoing clinical trials, which are already fully enrolled. Merck expects to have top-line results from two of the ongoing studies by the end of 2011 and from a third in the first half of 2012.

The FDA originally granted cladribine tablets a priority review in July 2010 and had expected to make a decision on the product by November 28, 2010. However, at that time, the agency extended its review period by three months to February 28, 2011, in order to allow time for a full review of additional information provided by Merck at the agency's request.

The product was approved in Russia in July 2010 and in Australia in September 2010.

The Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) issued a negative opinion regarding the marketing application for cladribine tablets as a treatment for relapsing-remitting MS.