Merck KGaA faces another wait before regulators in the USA decide whether to give the green light to the German firm's multiple sclerosis pill cladribine.

The US Food and Drug Administration has extended its review period for cladribine as a therapy for relapsing forms of MS by three months to February 28 next year. The agency had granted priority review status for the tablet in July of 2010, reducing the standard 10-month review period to six, which was set to end on November 28.

Now the FDA says it needs more time "for a full review of additional information provided under the New Drug Application", Merck noted, adding that  it is has been working closely with the agency during the review process.

The Darmstadt-based group will be hoping the US regulator looks more favourably on cladribine than its European counterpart. In September, the European Medicines Agency's Committee for Medicinal Products for Human Use issued a negative opinion, saying that based on currently available data the benefits of the drug do not outweigh its risks.

That EMA decision came days after Novartis' Gilenya (fingolimod) was approved by the FDA, putting it ahead of Merck in the race to be first with an MS pill in the main markets.
At present, cladribine has been approved in Russia and Australia.