Ireland’s Elan Corporation lost a staggering 58% of its stock market value in Ireland this morning after the company revealed a third person taking its suspended multiple sclerosis drug, Tysabri (natalizumab), had been diagnosed with a rare and potentially fatal immune system disease. Partner Biogen Idec’s share price dipped by 10% in pre-market trading on the Nasdaq Stock Exchange.

In a statement, the two firms said that the latest case had been diagnosed in a patient taking the drug in a Crohn’s disease clinical trial, and who died in December 2003. The patient in question had originally been diagnosed with malignant astrocytoma – a form of brain cancer.

Elan and Biogen Idec suspended sales and clinical trials of Tysabri late last month after one patient died from the condition – known as progressive multifocal leukoencephalopathy, or PML – during a clinical trial, which assessed Tysabri in combination with another Biogen Idec MS drug, Avonex (interferon beta-1a) [[01/03/05a]]. A second case was confirmed a few days later [[04/03/05a]]. The firms have since been reviewing all clinical trials involving Tysabri, and say that they are working to evaluate the approximately 3,000 in MS, Crohn’s disease, and rheumatoid arthritis studies.

Tysabri 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 Industry observers had expected it to ultimately become a $1 billion dollar a year drug.