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Biogen, Elan Near Tysabri Filing

The companies say they expect to wrap up a safety review within weeks.

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rose modestly after the drug companies updated investors on the regulatory status of their Tysabri drug.

The companies said late Tuesday they expect to complete their safety review of Tysabri "in the coming weeks." Then they expect to seek approval to reinstate the drug as a treatment for multiple sclerosis.

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The companies pulled Tysabri from the market on Feb. 28 following a report of a suspected rare brain disease -- progressive multifocal leukoencephalopathy, or PML -- linked to the drug. Subsequently, they said Tysabri was linked to PML in two MS patients and in one patient receiving the drug during a clinical trial for Crohn's Disease, an inflammatory gastrointestinal ailment. PML claimed the lives of two of the patients.

After the companies withdrew Tysabri, they embarked on an extensive review among patients who had participated in clinical trials for MS, Crohn's and rheumatoid arthritis. They suspended all clinical trials of the drug.

The safety review of the Crohn's disease and rheumatoid arthritis patients will be completed soon. On Aug. 9, the companies said they

found no new confirmed cases of PML among MS patients.

The companies said 91% of the more than 2,000 MS patients tested in clinical trials took part in the follow-up safety review, which also included an examination of any reports of potential PML in patients receiving Tysabri after the drug reached the U.S. market in November.

Tysabri had been approved for relapsing-remitting MS, the most common form of the disease at the time of diagnosis. It is characterized by acute symptoms or a worsening of neurological functions that can occur intermittently. These symptoms can weaken or disappear for months or years between relapses.

The companies didn't say how many Crohn's and rheumatoid arthritis patients are being evaluated.

Previously, the companies said the MS patients contracting the PML side effect took both Tysabri and Avonex, another MS drug from Biogen Idec, for more than 24 months. The Crohn's Disease patient took Tysabri and immunosuppressant drugs, a common treatment for certain inflammatory diseases.

Tuesday's announcement came after markets had closed. In regular trading, Elan's stock closed at $8.33, up 16 cents, or 1.7%. In after-hours trading, the stock gained 9 cents. In regular trading, Biogen Idec slipped 6 cents to $40.23. After hours, the stock rose 48 cents, or 1.2%.