FDA Approves the Reintroduction of TYSABRI(R) for the Treatment of Relapsing Forms of Multiple Sclerosis

Biogen Idec (NASDAQ: BIIB) and Elan Corporation, plc(NYSE: ELN) today announced the approval of a supplemental BiologicsLicense Application (sBLA) by the U.S. Food and Drug Administration(FDA) for the reintroduction of TYSABRI(R) (natalizumab) as amonotherapy treatment for relapsing forms of multiple sclerosis (MS)to slow the progression of disability and reduce the frequency ofclinical relapses. TYSABRI will be available upon the completion ofkey activities related to the risk management plan, including FDAreview of educational and training materials, internal validation ofsystems based on final FDA requirements and training of internalpersonnel. As such, the companies anticipate TYSABRI will be availablein July.

The FDA granted approval for reintroduction based on the review ofTYSABRI clinical trial data; revised labeling with enhanced safetywarnings; and a risk management plan (TOUCH Prescribing Program)designed to inform physicians and patients of the benefits and risksof TYSABRI treatment and minimize potential risk of progressivemultifocal leukoencephalopathy (PML). Because of the increased risk ofPML, TYSABRI monotherapy is generally recommended for patients whohave had an inadequate response to, or are unable to tolerate,alternate MS therapies.

"Today represents a significant step forward for people withrelapsing MS. The reintroduction of TYSABRI offers new hope as animportant therapeutic choice for patients living with this disablingdisease. TYSABRI has demonstrated compelling efficacy in MS, and webelieve the TOUCH Prescribing Program, designed in collaboration withthe FDA, will help patients and physicians assess the benefits andrisks of TYSABRI and make informed decisions about therapy," saidJames C. Mullen, Chief Executive Officer, Biogen Idec.

"We are pleased with the FDA's decision to once again make TYSABRIavailable to patients and their families suffering from this chronic,debilitating disease, " said Kelly Martin, Chief Executive Officer,Elan. "There continues to be a significant unmet medical need whereTYSABRI will be an important treatment option. "

Today's action follows a March 8, 2006 unanimous recommendation bythe FDA's Peripheral and Central Nervous System Drugs AdvisoryCommittee to allow the reintroduction of TYSABRI. Biogen Idec and Elanvoluntarily suspended TYSABRI from the U.S. market and all ongoingclinical trials in February 2005 based on reports of PML, anopportunistic viral infection of the brain that usually leads to deathor severe disability.

TOUCH Prescribing Program

TOUCH (TYSABRI Outreach: Unified Commitment to Health) PrescribingProgram was developed in conjunction with the FDA to facilitate theappropriate use of TYSABRI and to assess, on an ongoing basis, theincidence and risk factors for PML and other serious opportunisticinfections associated with TYSABRI treatment. This program representsBiogen Idec and Elan's commitment to making the unique benefits ofTYSABRI available in a responsible manner.

Elements of the TOUCH Prescribing Program include:

-- Revised labeling with a prominent boxed warning of the risk of PML; and warnings against concurrent use of TYSABRI with chronic immunosuppressant or immunomodulatory therapies, and patients who are immunocompromised due to HIV, hematological malignancies, organ transplants or immunosuppressive therapies

-- Mandatory enrollment for all prescribers, central pharmacies, infusion centers and patients who wish to prescribe, distribute, infuse, or receive, respectively, TYSABRI

-- Controlled, centralized distribution only to authorized infusion centers

-- Mandatory FDA-reviewed educational tools for patients and physicians, including a patient medication guide, TOUCH enrollment form and a monthly pre-infusion checklist

-- Ongoing assessment of PML risk and overall safety

-- A 5,000 patient cohort observational study over five years, the TYSABRI Global Observation Program in Safety (TYGRIS)

About TYSABRI

Two-year data from the AFFIRM monotherapy trial showed thattreatment with TYSABRI reduced the risk of disability progression by42% (p is less than 0.001), the primary endpoint of the study, and ledto a 67% reduction (p is less than 0.001) in the annualized relapserate compared to placebo. TYSABRI treatment also resulted in sustainedand statistically significant reductions in brain lesion activity asmeasured by MRI. The two-year data from the SENTINEL add-on trial alsodemonstrated that treatment with TYSABRI in addition to AVONEX(R)(Interferon beta-1a) had a significant effect on disabilityprogression, relapse rate and brain MRI disease activity compared toAVONEX alone.

TYSABRI increases the risk of PML, an opportunistic viralinfection of the brain that usually leads to death or severedisability. Three cases of PML occurred in clinical trial patients whowere concomitantly exposed to immunomodulators (interferon beta in thepatients with MS) or were immunocompromised due to recent treatmentwith immunosuppressants (e.g., azathioprine in the patient withCrohn's disease). Two of the cases were observed in 1,869 patientswith MS treated for a median of 120 weeks. A third case of PMLoccurred among 1,043 patients with Crohn's disease after the patientreceived eight doses. The number of cases is too few and the number ofpatients treated too small to reliably conclude that the risk of PMLis lower in patients treated with TYSABRI alone than in patients whoare receiving other drugs that decrease immune function or who areotherwise immunocompromised. Healthcare professionals should monitorpatients on TYSABRI for any new signs or symptoms that may besuggestive of PML. TYSABRI dosing should be withheld immediately atthe first sign or symptom suggestive of PML.

TYSABRI is contraindicated in patients who have or have had PML orwith known hypersensitivity to TYSABRI or any of its components. InPhase III placebo-controlled trials of TYSABRI in MS, the overallincidence and rate of other infections were balanced betweenTYSABRI-treated patients and controls. Herpes infections were slightlymore common in patients treated with TYSABRI. Commonly reportedinfections with TYSABRI included urinary tract infections, lowerrespiratory tract infections, gastroenteritis and vaginitis. Seriousopportunistic and other atypical infections have been observed inTYSABRI-treated patients, some of these patients were receivingconcurrent immunosuppressants.

The incidence and rate of other serious and common adverse eventsin clinical trials were similarly balanced between treatment groups.Serious events that occurred in TYSABRI-treated patients includedhypersensitivity reactions (e.g., anaphylaxis), depression andgallstones. Appendicitis was more common in patients receiving TYSABRIwith AVONEX. Common adverse events reported in TYSABRI-treatedpatients include infusion reactions, headache, fatigue, joint and limbpain, abdominal discomfort, diarrhea and rash.

For more information about TYSABRI please visit www.biogenidec.comor www.elan.com.

Webcast

The companies will host a joint webcast for the investmentcommunity tomorrow at 8:30 am ET, 1:30 pm GMT, which can be accessedthrough the companies' websites.

About Biogen Idec

Biogen Idec creates new standards of care in oncology, neurologyand immunology. As a global leader in the development, manufacturing,and commercialization of novel therapies, Biogen Idec transformsscientific discoveries into advances in human healthcare. For productlabeling, press releases and additional information about the company,please visit www.biogenidec.com.

About Elan

Elan Corporation, plc is a neuroscience-based biotechnologycompany committed to making a difference in the lives of patients andtheir families by dedicating itself to bringing innovations in scienceto fill significant unmet medical needs that continue to exist aroundthe world.

Elan shares trade on the New York, London and Dublin StockExchanges. For additional information about the company, please visitwww.elan.com.

Safe Harbor/Forward Looking Statements

This press release contains forward-looking statements regardingTYSABRI. These statements are based on the companies' current beliefsand expectations. The commercial potential of TYSABRI is subject to anumber of risks and uncertainties. Factors which could cause actualresults to differ materially from the companies' current expectationsinclude the risk that we may unable to adequately address concerns orquestions raised by FDA or other regulatory authorities, that concernsmay arise from additional data, that the incidence and/or risk of PMLor other opportunistic infections in patients treated with TYSABRI maybe higher than observed in clinical trials, or that the companies mayencounter other unexpected delays or hurdles. There is no assurancethat the companies will be able to market and sell TYSABRI outside ofthe United States. Drug development and commercialization involves ahigh degree of risk. For more detailed information on the risks anduncertainties associated with the companies' drug development andother activities, see the periodic and current reports that BiogenIdec and Elan have filed with the Securities and Exchange Commission.The companies assume no obligation to update any forward-lookingstatements, whether as a result of new information, future events orotherwise.