Biotech firms Biogen Idec (BIIB 2.14%) and Elan (ELN) announced in a press statement released Wednesday that they have filed for regulatory approval to expand the use of multiple sclerosis drug Tysabri with the FDA and the European Medicines Agency.

Tysabri is already approved by the FDA for patients showing resistance to other medications, but the newest filing would grant sales for first-line use -- or for newly diagnosed patients. An expansion of its approval would greatly help sales of Tysabri, which recorded revenues of $840 million through the first nine months of 2012.

Dr. Alfred Sandrock, Biogen Development Sciences senior vice president and chief medical officer, was quoted in the release as saying: "Many appropriate patients are already benefiting from TYSABRI. A first line approval would allow people with MS access to a highly efficacious treatment earlier in the course of the disease, potentially leading to better outcomes."

Some patients undergoing treatment with Tysabri have shown an increased risk of contracting progressive multifocal leukoencephalopathy (PML) leading to regulatory caution over the use of Tysabri. However, Biogen had a test approved last year to determine those with antibodies for the virus that causes PML, and the two companies are hoping to build a case for expanded Tysabri approval upon that. With approval, some analysts have said that Tysabri could reach annual sales of $2.9 billion by 2015.

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