Biogen Idec and Elan are suspending Tysabri clinical trials and conducting MRIs and physicals on trial participants as part of their voluntary marketing suspension of the multiple sclerosis therapy, the companies said.

The tests will determine the risk of progressive multifocal leukoencephalopathy in patients taking natalizumab.

All clinical trial participants "will have new MRIs taken and all will undergo physicals in the very near future," Elan CEO Kelly Martin said Feb. 28.

"In addition to that we are convening a panel of experts, PML experts, towards the end of the week."

The panel will discuss JC virus, the cause of PML, and the "the intersection between JC virus biology and immune regulation and disregulation," Biogen Idec Exec VP-Development Burt Adelman said.

On Feb. 28 Biogen Idec and Elan announced the suspension of Tysabri marketing based on reports of two serious adverse events that occurred in patients treated with natalizumab and Biogen Idec's Avonex (interferon beta-1a) (see ¹ Also see "Tysabri Could Return In Fall; Marketing Suspended By Biogen Idec And Elan" - Pink Sheet, 28 February, 2005.).

The events involve one fatal, confirmed case and one suspected case of PML.

Currently 3,000 patients are enrolled in trials for the treatment of MS, Crohn's disease and rheumatoid arthritis with Tysabri.

Tysabri was approved onNov. 23 for the treatment of MS based on one-year data from two Phase III trials (² Also see "Elan/Biogen Idec's Tysabri, Formerly Antegren, Approved For MS Based On One-Year Data" - Pink Sheet, 23 November, 2004.).

The expert panel will be asked to provide input on other necessary tests for the detection of PML.

"We're also going to talk to the experts this week to see if there are any other tests that we could do" to detect PML, Elan Exec VP-Global R&D Lars Ekman said.

"I'm not aware that this disease has a cryptic course such that the only evidence that a patient might have this disease is an unrecognized MRI lesion," Adelman said.

"My sense is that patients usually have clinical symptoms concurrent with MRI changes" but the panel may think differently, he added.

The panel will also help Biogen Idec and Elan understand PML progression.

"PML is caused by activation of the JC virus that resides in latent form in as many as 80% of healthy adults. The factors leading to activation of the latent infection are not fully understood and we will certainly be learning more about that in the near future," Adelman said.

Following the marketing suspension, Biogen Idec's Tysabri sales force will help promote Avonex and assist prescribers until the drug is reintroduced (see ³ Also see "Biogen Idec Shifting Tysabri Sales Force To Avonex Detail" - Pink Sheet, 28 February, 2005.).

- Andrew Shelton

Tysabri Study Participants To Undergo MRI, Physical In Search For Cause Of Adverse Events

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