Troubled Irish company, Elan Corporation, which has witnessed a sharp decline in its share price since suspending sales of its multiple sclerosis drug, Tysabri (natalizumab), earlier this year after a clinical trial patient died from a rare central nervous system infection [[01/03/05a]], enjoyed a resurgence in its popularity with investors this morning. The firm’s share price leapt by more than 20% during morning trading on the Irish Stock Exchange after it revealed that Tysabri significantly delayed the progression of disability, rate of clinical relapses and brain lesions in patients with relapsing forms of MS.

The two-year data from the 942-patient Affirm Phase III monotherapy trial were presented yesterday at the American Academy of Neurology and showed that treatment with Tysabri led to a 42% reduction in the risk of disability progression compared to placebo. It reduced the rate of relapses by 67% and showed a 76% reduction in the mean number of new lesions versus placebo.

Side effects seen in the two-year trial were consistent with previously reported one-year data, and included headache, fatigue, urinary tract infection, depression, lower respiratory tract infection, and limb and joint pain. Serious infections occurred in 3.2% and 2.6% of Tysabri- and placebo-treated patients respectively.

“We are very encouraged by the two-year results which support the efficacy of Tysabri in MS,” said Lars Ekman, executive vice president and president of research and development at Elan. “Patient safety is our top priority, and we are working closely with the regulatory agencies to define the appropriate benefit-risk profile for Tysabri as a new option to treat MS,” he added.

The drug had been expected to be a bit earner for Elan and partner, Biogen Idec, and its suspension has been a significant blow for both firms [[04/04/05a]], [[12/04/05b]], [[16/03/05c]].