Panel Supports Tysabri Return

Biogen's shares were also halted while the two-day meeting was taking place, and they resumed trading in after-hours activity, climbing $3.90, or 8.6%, to $49.40.

Meanwhile, Teva (TEVA Quote), the maker of an MS medication called Copaxone, slipped 22 cents to $40.89. Serono (SRA Quote), which sells the MS drug Rebif, lost 56 cents to $17.32.

The reach of those two products provides an idea of the size of the market Biogen and Elan are hoping to rejoin. Rebif had sales of $1.27 billion last year, and Copaxone sales totaled $1.18 billion in 2005.

On Tuesday, the panel heard emotional testimony from MS patients who say Tysabri succeeded in improving their lives after other treatments had failed. The drug's supporters touched on a common theme -- that they simply want the choice of using Tysabri.

Tysabri was withdrawn after being connected to a disease called progressive multifocal leukoencephalopathy. Two PML cases appeared in patients who took Tysabri for multiple sclerosis along with another Biogen MS treatment, Avonex. A patient who received Tysabri during a Crohn's disease trial was later found to have PML. In two of the cases, the patients died.

Following the PML cases, Biogen and Elan performed a safety evaluation of more than 3,000 Tysabri patients, but found no new confirmed cases of the disease beyond the three that had been reported. Biogen and Elan are equal partners in the drug.

MS is a chronic, debilitating disease that affects the brain and spinal cord. MS is thought to be an autoimmune disease, and while it isn't considered deadly, it can severely compromise a patient's quality of life, possibly leading to numbness, difficulty thinking and coordination and speech problems. People with MS can become severely disabled, but most don't, according to the National Multiple Sclerosis Society.