At the end of February this year the companies voluntarily suspended Tysabri from the US market and all ongoing clinical trials based on reports of progressive multifocal leukoencephalopathy (PML), a rare and potentially fatal disease of the central nervous system. There were three confirmed cases of PML in patients taking the drug, two of which were fatal.
In August the companies announced the completion of the safety evaluation of Tysabri in MS, which resulted in no new confirmed cases of PML, and the companies are now ready to set about re-establishing the drug in the market.
Many observers had predicted that Tysabri would be a big selling drug for the companies on its release in November 2004, making the reports of PML in patients and the subsequent market suspension of the drug a major blow for the companies.
The company has also announced that it will complete the safety evaluation of Tysabri in Crohn’s disease and rheumatoid arthritis in the coming weeks.