Elan and Biogen Idec Announce That FDA Will Extend Regulatory Review Period for TYSABRI(R) for Crohn's Disease

Elan Corporation, plc (NYSE: ELN) and Biogen Idec (NASDAQ: BIIB)
today announced that the U.S. Food and Drug Administration (FDA)
informed the companies that the Agency will extend its regulatory
review of TYSABRI(R) (natalizumab) as a treatment for Crohn's disease
by up to 3 months.

The companies have been informed by the FDA that the Agency
requires additional time to review information regarding the proposed
TYSABRI risk management plan for Crohn's disease. Under this revised
timeline, the companies anticipate action from FDA on or before
January 13, 2008.

About Crohn's Disease

Approximately one million people worldwide have Crohn's disease, a
chronic and progressive inflammatory disease of the gastrointestinal
tract, which commonly affects both men and women.

The disease usually causes diarrhea and crampy abdominal pain,
often associated with fever, and at times rectal bleeding. Loss of
appetite and weight loss also may occur. Complications include
narrowing of the intestine, obstruction, abscesses, and fistulas
(abnormal channels connecting the intestine and other organs,
including the skin), and malnutrition. Most patients eventually
require surgery, which has both risks and potential short- and
long-term complications.

Crohn's disease can have a devastating impact on the lifestyle of
patients, many of whom are young and active. Currently there is no
medical or surgical cure for Crohn's disease. Many patients fail to
respond to current therapies, including biological therapies such as
agents that inhibit tumor necrosis factor alpha (TNF-alpha). Due to
this failure of current therapies in CD, therapies that have novel
biological targets are required.

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 less than 0.001) in the annualized relapse rate compared
to placebo and reduced the relative risk of disability progression by
42-54% (p less than 0.001).

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 trials, the incidence and rate of
other serious and common adverse events, including the overall
incidence and rate of infections, were balanced between treatment
groups. Common adverse events reported in TYSABRI-treated patients
include headache, fatigue, infusion reactions, urinary tract
infections, joint and limb pain, and rash.

In addition to the United States and European Union, TYSABRI is
also approved for MS in Switzerland, Canada, Australia, New Zealand
and Israel. TYSABRI was discovered by Elan and is co-developed with
Biogen Idec.

For more information about TYSABRI please visit www.tysabri.com,
www.biogenidec.com or www.elan.com, or call 1-800-456-2255.

About Elan

Elan Corporation, plc is a neuroscience-based biotechnology
company committed to making a difference in the lives of patients and
their families by dedicating itself to bringing innovations in science
to fill significant unmet medical needs that continue to exist around
the world. Elan shares trade on the New York, London and Dublin Stock
Exchanges. For additional information about the company, please visit
www.elan.com.

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.

Safe Harbor/Forward-Looking Statements

This press release contains forward-looking statements regarding
TYSABRI. These statements are based on the companies' current beliefs
and expectations. The commercial potential of TYSABRI is subject to a
number of risks and uncertainties. Factors which could cause actual
results to differ materially from the companies' current expectations
include the risk that we may be unable to adequately address concerns
or questions raised by FDA or other regulatory authorities, that
concerns may arise from additional data, that the incidence and/or
risk of PML or other opportunistic infections in patients treated with
TYSABRI may be higher than observed in clinical trials, or that the
companies may encounter other unexpected hurdles. Drug development and
commercialization involves a high degree of risk.

For more detailed information on the risks and uncertainties
associated with the companies' drug development and other activities,
see the periodic and current reports that Biogen Idec and Elan have
filed with the Securities and Exchange Commission. The companies
assume no obligation to update any forward-looking statements, whether
as a result of new information, future events or otherwise.