Elan drops 3.6% on new Tysabri PML case

Shares in Irish biotechnology firm Elan fell 3.6% on December 15 after it was reported that another patient taking its lead product, the multiple sclerosis drug Tysabri (natalizumab), contracted a rare brain disease.

In third-quarter 2008, global net sales of the predicted blockbuster, co-developed with Biogen Idec, were $236.0 million, beating expectations despite six earlier reports of progressive multifocal leukoencephalopathy. This rare disease is caused by a virus that normally lies dormant but can strike patients taking drugs like Tysabri, which impair the immune system.