XenoPort and GlaxoSmithKline Mutually Agree to Terminate Their Collaboration on Horizant

  XenoPort and GlaxoSmithKline Mutually Agree to Terminate Their Collaboration
  on Horizant

         XenoPort Reacquires Rights to Horizant in the United States

Business Wire

SANTA CLARA, Calif. -- November 08, 2012

XenoPort, Inc. (Nasdaq:XNPT) announced today that it has reached an agreement
with Glaxo Group Limited (GSK) to terminate their collaboration agreement
concerning Horizant® (gabapentin enacarbil) Extended-Release Tablets, for
which GSK held commercialization rights and certain development rights in the
United States.

Pursuant to a termination and transition agreement entered into between the
parties, GSK is returning Horizant rights to XenoPort and providing certain
assistance during a transition period. The termination and transition
agreement also provides for a mutual release of claims and resolves all
ongoing litigation between the parties. XenoPort acknowledges that GSK
fulfilled its contractual obligations on the development, manufacturing and
commercialization of Horizant.

During the transition period that will end on April 30, 2013, GSK will
continue to exclusively commercialize, promote, manufacture and distribute
Horizant in the United States. XenoPort will not be responsible for any losses
associated with the terminated collaboration agreement, and XenoPort will not
receive any revenue or incur any losses from GSK’s sales of Horizant during
the transition period. GSK will also continue to fully fund the costs
associated with the management and conduct of clinical studies initiated by
GSK prior to the date of the termination and transition agreement. In
addition, prior to the end of the transition period, GSK will provide to
XenoPort inventory of gabapentin enacarbil in GSK’s possession that is not
required for use by GSK in the manufacture of Horizant. In exchange for such
inventory, XenoPort will make annual payments to GSK of $1.0 million for six
years beginning in 2016.

Following the transition period, XenoPort will assume all responsibilities for
further development, manufacturing and commercialization of Horizant in the
United States. GSK has also agreed that, if requested by XenoPort, GSK will
continue to supply Horizant tablets to XenoPort for up to an additional six
months following the transition period on pricing terms established under the
termination and transition agreement and to be further memorialized in a
supply agreement to be entered into between the parties.

As part of the termination and transition agreement, GSK is purchasing $20.0
million of common stock of XenoPort, or an aggregate of 1,841,112 shares at
$10.863 per share, which per share price represents a 12.5 percent premium to
the average of the closing prices of XenoPort’s common stock for the 10
trading days prior to October 31, 2012. In addition, subject to the conditions
and limitations set forth in a separate stock purchase agreement entered into
between the parties, during the next six months, XenoPort has the option to
require GSK to purchase up to an additional $20.0 million of common stock of
XenoPort at a 12.5 percent premium to the average of the closing prices of
XenoPort’s common stock for the 10 trading days prior to the day XenoPort
notifies GSK of its decision to exercise this option.

Conference Call

XenoPort will host a conference call at 8:30 a.m. Eastern Time today to
discuss matters related to the termination and transition agreement between
GSK and XenoPort. To access the conference call via the Internet, go to
www.XenoPort.com. To access the live conference call via phone, dial
1-888-275-3514. International callers may access the live call by dialing
706-679-1417. The reference number to enter the call is 69518395.

The replay of the conference call may be accessed after 8:30 a.m. Eastern Time
today via the Internet, at www.XenoPort.com, or via phone at 1-800-642-1687
for domestic callers, or 706-645-9291 for international callers. The reference
number to enter the replay of the call is 69518395. Dial-in access to the
replay of the call will be available for approximately one week, and the
Internet replay of the call will be available for approximately one month
following the live call.

About XenoPort

XenoPort is a biopharmaceutical company focused on developing and
commercializing a portfolio of internally discovered product candidates for
the potential treatment of neurological disorders. GlaxoSmithKline holds
commercialization rights for Horizant in the United States during a transition
period, following which XenoPort will be responsible for Horizant’s further
development, manufacturing and commercialization. Regnite® (gabapentin
enacarbil) Extended-Release Tablets is approved for the treatment of
moderate-to-severe primary restless legs syndrome in Japan. Astellas Pharma
Inc. holds all development and commercialization rights for Regnite in Japan
and five other Asian countries. XenoPort holds all other world-wide rights to
gabapentin enacarbil. XenoPort’s pipeline of product candidates includes
potential treatments for patients with spasticity, Parkinson’s disease and
relapsing-remitting multiple sclerosis.

To learn more about XenoPort, please visit the Web site at www.XenoPort.com.

Forward-Looking Statements

This press release contains "forward-looking" statements, including, without
limitation, all statements related to the transition of all Horizant product
rights to XenoPort and the timing thereof; transition activities, including
GSK’s conduct and funding of clinical trials; XenoPort’s election of its
option to require GSK to purchase additional shares of its common stock; the
terms of a future supply agreement, if any; and the continued availability of
Horizant to patients. Words such as “will,” “would” and similar expressions
are intended to identify forward-looking statements. These forward-looking
statements are based upon XenoPort’s current expectations. Forward-looking
statements involve risks and uncertainties. XenoPort’s actual results and the
timing of events could differ materially from those anticipated in such
forward-looking statements as a result of these risks and uncertainties, which
include, without limitation, risks related to XenoPort’s dependence on GSK for
further development, manufacturing and commercialization of Horizant during
the transition period and as a potential source of supply thereafter; GSK’s
ability to fund and conduct clinical trials as agreed between the parties;
XenoPort’s ability to satisfy the conditions precedent to the exercise of its
option to require GSK to purchase additional shares of its common stock;
XenoPort’s ability to establish sales, marketing and distribution capabilities
to market Horizant following the transition period, or to enter into
arrangements with third parties to do so, including the risk that XenoPort’s
failure to establish or contract for these capabilities could interrupt, delay
or otherwise adversely affect the commercialization of Horizant; and
XenoPort’s cash position and need for additional capital. These and other risk
factors are discussed under the heading "Risk Factors" in XenoPort’s Quarterly
Report on Form 10-Q for the quarter ended September 30, 2012, filed with the
Securities and Exchange Commission on October 25, 2012. XenoPort expressly
disclaims any obligation or undertaking to release publicly any updates or
revisions to any forward-looking statements contained herein to reflect any
change in the company's expectations with regard thereto or any change in
events, conditions or circumstances on which any such statements are based.

XENOPORT, Regnite and Horizant are registered trademarks of XenoPort, Inc.

XNPT2F

Contact:

XenoPort, Inc.
Jackie Cossmon, 408-616-7220
ir@XenoPort.com