Ireland’s Elan Corporation’s share price fell further on the European stock markets this morning on news that a second case of a rare, but potentially fatal, central nervous system disease had been confirmed in a patient taking the company’s multiple sclerosis offering Tysabri (natalizumab).

Elan and partner, Biogen Idec, suspended sales and clinical trials of Tysabri earlier this week after one patient taking the drug died from the condition – known as progressive multifocal leukoencephalopathy, or PML [[01/03/05a]]. At the time, they said that a second patient was also thought to be suffering from the condition, but this had yet to be confirmed.

Elan’s shares slumped almost 17% in Ireland during morning trading – meaning the company has lost some 75% of its value since the Tysabri suspension. The drug had been seen as key to helping the Irish firm, which teetered on the brink of bankruptcy in 2002 [[10/06/02a]], succeed in its turnaround. The product won coveted US approval in November [[24/11/04a]], and Elan had been expecting it to ultimately become the market-leading treatment for all forms of relapsing remitting MS [[08/02/05a]].

- Meanwhile, a shareholder class action lawsuit has been filed against Biogen Idec. Specifically, the lawsuit alleges that Biogen Idec’s chairman, William Rastetter, and chief executive, James Mullen “failed to disclose and misrepresented… material adverse facts” about Tysabri – namely that Tysabri posed serious immune-system side effects and made patients susceptible to PML by changing the way certain white blood cells function. In addition, the suit claims that the company “concealed these facts in order to fast track Tysabri for [US Food and Drug Administration] approval so that [it] could reap the financial benefits from the sales of the drug.”

Almost 43% was knocked off Biogen Idec’s share price on the back of the Tysabri suspension.