Biogen Idec Announces Multiple Sclerosis Franchise and Pipeline Presentations at the 60th Annual Meeting of the American Academy of Neurology

Biogen Idec (NASDAQ: BIIB) today announced that 17
company-sponsored plenary sessions, platform presentations, and poster
presentations will be presented during the 60th Annual Meeting of the
American Academy of Neurology. These presentations will cover four
compounds that are marketed or currently in development by Biogen Idec
and its partners for the treatment of multiple sclerosis (MS). This
includes two approved therapies for MS; TYSABRI(R) (natalizumab) and
AVONEX(R) (Interferon beta-1a); and two additional agents in
development; BG-12 (dimethyl fumarate) and daclizumab.

"The presentations and posters at AAN show Biogen Idec´s broad
commitment to those living with MS," said Michael Panzara, MD, MPH

Vice President and Chief Medical Officer, Neurology Strategic Business
Unit, Biogen Idec. "No company is doing more for patients with MS than
Biogen Idec. We have been a leader in developing and commercializing
therapies, with two products on the market to help treat MS, and four
additional development programs that target other potential pathways
of the disease. Through additional development and research, our hope
is that we will be able to both treat the symptoms of MS and
eventually reverse the damaging effects that are a result of the
disease."

The following are selected highlights of presentations during the
meeting:

TYSABRI

Platform Presentations

-- Natalizumab Utilization and Safety in Patients with Relapsing

Multiple Sclerosis: Updated Results from TOUCH(TM) and TYGRIS

(Presentation #S02.002 - Tuesday, April 15, 2:15 p.m. CDT)

-- The Safety of TYSABRI Re-Dosing and Treatment (STRATA) Study

(Presentation #S02.003 - Tuesday, April 15, 2:30 p.m. CDT)

-- Statistical Analysis of Clinical Endpoints in Studies of

Disease-Modifying Therapies for Multiple Sclerosis

(Presentation #S02.001 - Tuesday, April 15, 2:00 p.m. CDT)

-- Plasma Exchange Accelerates the Decline of Serum Natalizumab

Concentration in Patients with Multiple Sclerosis: Results of

the Natalizumab PLEX Study (Presentation #S22.005 - Wednesday

April 16, 3:00 p.m. CDT)

-- Plasma Exchange Augments Leukocyte Transmigration across an In

Vitro Blood-Brain Barrier in Natalizumab-Treated Patients with

Multiple Sclerosis (Presentation #S27.005 - Wednesday, April

16, 3:00 p.m. CDT)

Poster Presentations

-- Natalizumab Increases the Proportion of Patients Free of

Clinical or MRI Disease Activity in Relapsing Multiple

Sclerosis (Poster #P02.156 - Tuesday, April 15, 11:30 a.m. -

2:30 p.m. CDT)

-- Natalizumab Reduces Multiple Sclerosis Severity: Analysis of

Patients from the AFFIRM and SENTINEL Studies Using the

Multiple Sclerosis Severity Scale (Poster #P04.169 -

Wednesday, April 16, 7:00 - 10:00 a.m. CDT)

-- Pain in Patients with Multiple Sclerosis: Effects of

Natalizumab (Poster #P04.181 - Wednesday, April 16, 7:00 -

10:00 a.m. CDT)

-- Impact of Natalizumab on Multiple Sclerosis Patient-Reported

Experiences: A Cross Sectional Survey (Poster #P05.065 -

Wednesday, April 16, 4:00 - 7:00 p.m. CDT)

AVONEX

-- Progression of Disability over 2 Years Predicts Disability at

8 Years in Relapsing Multiple Sclerosis: Analysis from the

Phase 3 Clinical Trial of Intramuscular Interferon Beta-1a

(Poster #P04.156 - Wednesday, April 16, 7:00 - 10:00 a.m. CDT)

-- Multiple Sclerosis Patients Taking Interferon Beta-1a Have

Full Biological Activity in Both Stable and Breakthrough

Disease (Poster #P07.150 - Thursday, April 17, 11:30 a.m. -

2:30 p.m. CDT)

-- Safety and Tolerability of the First Single-Use, Fully

Integrated Autoinjector for IM Interferon Beta-1a (Poster

#P02.144 - Tuesday, April 15, 11:30 a.m. - 2:30 p.m. CDT)

-- Incidence of Binding and Neutralizing Antibodies in Sera and

Cerebrospinal Fluid of Patients with Relapsing-Remitting

Multiple Sclerosis Treated with Interferon Beta (Poster

#P05.084 - Wednesday, April 16, 4:00 - 7:00 p.m. CDT)

-- Efficacy of Interferon Beta-1a in Patients with Chronic

Inflammatory Demyelinating Polyradiculoneuropathy (CIDP)

(Poster #P07.101 - Thursday, April 17, 11:30 a.m. - 2:30 p.m.

CDT)

BG-12

BG-12 (dimethyl fumarate) is an oral, small molecule
immuno-modulator in Phase III development for relapsing forms of MS.

-- The Efficacy of BG00012 in Patients with Relapsing-Remitting

Multiple Sclerosis: Subgroup Analyses from the Phase 2b Study

(Poster #P02.134 - Tuesday, April 15, 11:30 a.m. - 2:30 p.m.

CDT)

-- Activation of Nrf2 and Modulation of Disease by BG00012

(Dimethyl Fumarate) Suggest a Dual Cytoprotective and

Anti-Inflammatory Mechanism of Action (Poster #P01.085 -

Tuesday, April 15, 7:00 - 10:00 a.m. CDT)

Daclizumab

Daclizumab is a humanized monoclonal antibody specific for the
IL-2 receptor of T cells that is in Phase II development for MS.

-- A Phase 2 Randomized, Double-Blinded, Placebo-Controlled

Multicenter Study of Subcutaneous Daclizumab, a Humanized

Anti-CD-25 Monoclonal Antibody, in Patients with Active

Relapsing Forms of Multiple Sclerosis - Week 44 Results

(Plenary session #PL01.003 - Wednesday, April 16, 9:00 a.m.

CDT)

Corporate Therapeutic Update

On April 15, Biogen Idec will be hosting a symposium for meeting
attendees entitled "We´re Taking the Future of MS Personally -
Corporate Therapeutic Update from Biogen Idec: MS, Biogen Idec, and
the Future of Personalized Medicine." The symposium will provide an
update on Biogen Idec´s multiple sclerosis and neurology products and
drug development pipeline, as well as a presentation on the future of
personalized medicine in MS by Philip L. De Jager, MD, PhD, Assistant
Professor of Neurology at Harvard Medical School. A panel discussion
focused on the role of personalized medicine in the future, as well as
the need to treat decisively with medications available now, will also
be part of the symposium and will include Dr. De Jager, Dr. Panzara

moderator Bruce A. Cree, MD, PhD, MCR, Assistant Professor of
Neurology, Multiple Sclerosis Center at University of California San
Francisco; Dusan Stefoski, MD, Director, Rush Multiple Sclerosis
Center; Associate Professor of Neurology, Rush University Medical
College; Ralf Gold, MD, Professor and Chair, Department of Neurology

St. Josef Hospital, Ruhr University (Germany); and Steven L. Galetta

MD, Van Meter Professor of Neurology, University of Pennsylvania
School of Medicine.

MS Simulator

Biogen Idec will have an MS simulator for attendees to use

allowing them to experience the symptoms many patients with MS suffer.
The simulator will be available on the exhibit hall floor during the
meeting.

About Biogen Idec

Biogen Idec creates new standards of care in therapeutic areas
with high unmet medical needs. Founded in 1978, Biogen Idec is a
global leader in the discovery, development, manufacturing, and
commercialization of innovative therapies. Patients in more than 90
countries benefit from Biogen Idec´s significant products that address
diseases such as lymphoma, multiple sclerosis, and rheumatoid
arthritis. For product labeling, press releases and additional
information about the company, please visit www.biogenidec.com.

About Our Marketed Products and Development Pipeline

About TYSABRI

TYSABRI is a treatment approved for relapsing forms of MS in the
United States and relapsing-remitting MS in the European Union.
According to data that have been published in the New England Journal
of Medicine, after two years, TYSABRI treatment led to a 68% relative
reduction (p<0.001) in the annualized relapse rate compared to placebo
and reduced the relative risk of disability progression by 42-54%
(p<0.001).

TYSABRI was recently approved to induce and maintain clinical
response and remission in adult patients with moderately to severely
active Crohn´s disease (CD) with evidence of inflammation who have had
an inadequate response to, or are unable to tolerate, conventional CD
therapies and inhibitors of TNF-alpha.

TYSABRI increases the risk of progressive multifocal
leukoencephalopathy (PML), an opportunistic viral infection of the
brain that usually leads to death or severe disability. Other serious
adverse events that have occurred in TYSABRI-treated patients included
hypersensitivity reactions (e.g., anaphylaxis) and infections. Serious
opportunistic and other atypical infections have been observed in
TYSABRI-treated patients, some of whom were receiving concurrent
immunosuppressants. Herpes infections were slightly more common in
patients treated with TYSABRI. In MS and CD clinical trials, the
incidence and rate of other serious adverse events, including serious
infections, were similar in patients receiving TYSABRI and those
receiving placebo. Common adverse events reported in TYSABRI-treated
MS patients include headache, fatigue, infusion reactions, urinary
tract infections, joint and limb pain, and rash. Other common adverse
events reported in TYSABRI-treated CD patients include respiratory
tract infections and nausea. Clinically significant liver injury has
been reported in patients treated with TYSABRI in the post-marketing
setting.

TYSABRI is approved in more than 30 countries including the United
States and many countries throughout the European Union, as well as
Switzerland, Canada, Australia, New Zealand and Israel.

For more information about TYSABRI please visit www.tysabri.com

www.biogenidec.com or www.elan.com, or call 1-800-456-2255.

About AVONEX

AVONEX is the most prescribed treatment for relapsing forms of MS
worldwide, with more than 130,000 patients on therapy. It is used
worldwide as a treatment for relapsing forms of MS to slow the
progression of disability and reduce relapses. AVONEX is also approved
for patients who have their first clinical MS attack and have a brain
MRI scan consistent with MS.

The most common side effects associated with AVONEX multiple
sclerosis treatment are flu-like symptoms, including myalgia, fever

fatigue, headache, chills, nausea, vomiting, pain and asthenia.

AVONEX should be used with caution in patients with depression or
other mood disorders and in patients with seizure disorders. AVONEX
should not be used by pregnant women. Patients with cardiac disease
should be closely monitored. Patients should also be monitored for
signs of hepatic injury. Routine periodic blood chemistry and
hematology tests are recommended during treatment with AVONEX. Rare
cases of anaphylaxis have been reported. Please see complete
prescribing information available at www.AVONEX.com.

About BG-12

BG-12 is currently in Phase III clinical development.

About Daclizumab

Daclizumab is currently in Phase II clinical development. Biogen
Idec is developing daclizumab for MS in collaboration with PDL
BioPharma, Inc.

Safe Harbor

This press release contains forward-looking statements about our
marketed products and our products in development. Drug development
and commercialization involves a high degree of risk, and all of our
products are subject to a number of risks and uncertainties. Important
risk factors include the risk that we may be unable to adequately
address concerns or questions raised by FDA or other regulatory
authorities, the occurrence of adverse safety events with our
products, that concerns may arise from additional data, that we may
not be able to get the drugs in development approved and that the
incidence and/or risk of any safety issues with respect to our
products may be higher than observed in clinical trials. The company
may also encounter other unexpected hurdles. Additional risks and
uncertainties that are described in Item 1.A. Risk Factors in our
reports on Form 10-K and Form 10-Q and in other periodic and current
reports we file with the SEC. These forward-looking statements speak
only as of the date of this press release, and we do not undertake any
obligation to publicly update any forward-looking statements, whether
as a result of new information, future events, or otherwise.