Elan Corp. of Ireland and Biogen Idec Inc. of Massachusetts jointly developed the drug to suppress the symptoms of multiple sclerosis, which attacks the body's central nervous system, and Crohn's, which inflames the gastrointestinal system.
The drug hit the market last year in the U.S., but was withdrawn after two patients suffered a rare brain disease called progressive multifocal leukoencephalopathy, or PML. One of those patients died.
In March 30, both companies also announced that a patient with Crohn's had also died after taking Tysabri.
Elan and Biogen decline to comment on recent reports, by both The Boston Globe and The Wall Street Journal, about a possible fourth and fifth case of PML in Tysabri users.
The companies say a third-phase testing trial of 510 Crohn's sufferers had produced reduced symptoms within 12 weeks of treatment.
Lars Ekman, Elan's president of research and development, says the results were being sent to the FDA in hopes a decision would be reached on whether Tysabri can be returned to the market.
