Shares in the Irish pharmaceutical company, Élan, tumbled 25% this morning after reports a fourth patient taking its multiple sclerosis drug, Tysabri, may have contracted the rare brain disease PML.
Tysabri was withdrawn earlier this year when it emerged that two people using it had died and a third contracted PML, a disease which hampers the central nervous system, often fatally.
At the company’s annual general meeting last week, Élan chief executive Kelly Martin said he was very confident that Tysabri would return to the market.
The news of the potential fourth case came in a report in the Boston Globe newspaper, which said that Biogen, Élan’s partner in developing the drug, had told the US Food and Drug Administration about the patient.
The newspaper said that the possible fourth patient is a 48-year-old woman who was taking Tysabri along with Avonex, another MS drug sold by Biogen.
The possible new case is the third among MS patients who were taking both Tysabri and Avonex, according to the FDA report.
Some doctors have speculated that the two drugs may together sufficiently weaken patients' immune systems to permit infections like PML.
The three confirmed PML patients also had weakened immune systems, sparking hope that Tysabri could return to the market if it was not used in conjunction with Avonex, according to the Boston Globe.
