TYSABRI PHASE III TRIAL IN CROHN'S DISEASE MEETS PRIMARY

Elan and Biogen Idec announced that ENCORE, the second Phase III induction trial of Tysabri for the treatment of moderately to severely active Crohn's disease (CD) in patients with evidence of active inflammation, met the primary endpoint of clinical response as defined by a 70 point decrease in baseline Crohn's Disease Activity Index (CDAI) score at both weeks eight and 12.

In addition, ENCORE met all of its secondary endpoints including clinical remission at both weeks eight and 12. Clinical remission was defined as achieving a CDAI score of equal to or less than 150 at both weeks eight and 12.

There were no notable differences in the overall rates of adverse events or serious adverse events between the Tysabri (natalizumab) and placebo treatment groups. The most common adverse events seen in the trial were headache, nausea, abdominal pain and nasopharyngitis.

On Feb. 28, 2005, Elan and Biogen Idec announced that they voluntarily suspended Tysabri from the U.S. market and all ongoing clinical trials. This decision was based on reports of progressive multifocal leukoencephalopathy (PML), a rare and potentially fatal, demyelinating disease of the central nervous system. Elan and Biogen Idec's comprehensive safety evaluation concerning Tysabri and any possible link to PML is ongoing. At the time of the dosing suspension, all ENCORE study patients had completed dosing based on the study protocol and collection and analysis of data followed.

The full data from ENCORE, including further subanalysis of response and remission rates as well as clinical effect at other time points, effect on inflammatory markers and quality of life data will be presented at an upcoming medical meeting.

ENCORE was a Phase III, international, double-blind, placebo-controlled study of 510 patients at 114 sites to evaluate the safety and efficacy of intravenous Tysabri in patients with moderately to severely active Crohn's disease (based on a confirmed diagnosis of CD and a CDAI score of greater than or equal to 220 and less than or equal to 450) and evidence of active inflammation (as evidenced by elevated C-reactive protein (CRP) levels of CRP greater than 2.87 mg/l, the upper limit of normal). Patients were randomized 1:1 to treatment with Tysabri (300mg) or placebo infusions at Weeks 0, 4, and 8. Efficacy and safety assessments were performed at Weeks 4, 8 and 12, and the study remains ongoing for safety follow-up.