Élan and partner Biogen Idec’s multiple sclerosis drug Tysabri (natalizumab) could be making a return to the market, after the firms said they planned to file a new application to the US Food and Drug Administration in the coming weeks following completion of a safety evaluation in the secondary indications of Crohn’s disease and rheumatoid arthritis. This adds to the already-completed investigation in MS patients, which showed no new confirmed cases of the rare brain disease PML (progressive multifocal leukoencephalopathy).

Tysabri was removed from the market earlier this year – just three months after its US approval - after one patient died from this demyelinating disease of the central nervous system [[24/11/04a]], [[01/03/05a]]. The companies have since reported three confirmed cases of PML, two of which were fatal.

In August, though, the firms said Tysabri – once expected to become a major blockbuster – had not uncovered any additional cases of PML [[09/08/05a]]. In a statement at the time, Elan and Biogen Idec noted that they planned to pursue regulatory submissions for Tysabri in Crohn's disease and rheumatoid arthritis in the third quarter and are "taking preliminary steps to restart clinical trials in MS." The safety review evaluated more than 90% of the 2,000 eligible patients from clinical studies by conducting both a neurological exam and a magnetic resonance imaging scan to determine any adverse effects of Tysabri. No new confirmed cases of PML were identified.

Analysts have suggested that Tysabri could make a re-appearance on the market as soon as next year.