GSK and XenoPort Announce Plans to Withdraw and Resubmit New Drug Application Requesting Approval of Solzira(TM) for Restless Legs Syndrome

GlaxoSmithKline (NYSE: GSK) and XenoPort, Inc. (Nasdaq: XNPT) announced today that the New Drug Application (NDA) for Solzira™ (gabapentin enacarbil) Extended Release Tablets for the treatment of moderate-to-severe primary Restless Legs Syndrome (RLS) has been withdrawn. The United States Food and Drug Administration (FDA) has requested that the data in a single study be reformatted. In addition, GSK will conduct a review of other trial data sets taking this input into account. The withdrawal does not relate to the content of the filing. GSK plans to resubmit the NDA quickly once this work is complete.

The resubmission will lead to a delay in the receipt by XenoPort of milestone payments of $23 million in the aggregate from GSK and Astellas Pharma Inc., which are associated with the acceptance by the FDA of the NDA for Solzira.

About SOLZIRA

Solzira is a new chemical entity that is designed to improve upon the pharmacokinetics of gabapentin by taking advantage of high-capacity transport mechanisms in the gastrointestinal tract to improve absorption.

About GlaxoSmithKline

GlaxoSmithKline is one of the world's leading research-based pharmaceutical and healthcare companies and is committed to improving the quality of human life by enabling people to do more, feel better and live longer. For more information, visit GlaxoSmithKline at www.gsk.com.

About XenoPort

XenoPort, Inc. is a biopharmaceutical company focused on developing a portfolio of internally discovered product candidates that utilize the body’s natural nutrient transport mechanisms to improve the therapeutic benefits of existing drugs. XenoPort is developing its lead product candidate in partnership with Astellas Pharma Inc. and GlaxoSmithKline. XenoPort’s product candidates are also being studied for the potential treatment of GERD, migraine headaches, neuropathic pain, spasticity related to spinal chord injury, acute back spasms and Parkinson’s disease. To learn more about XenoPort, please visit the Web site at www.XenoPort.com.

GlaxoSmithKline Forward-Looking Statement

Under the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995, GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Factors that may affect GSK' s operations are described under 'Risk Factors' in the 'Business Review' in the company' s Annual Report on Form 20-F for 2007.

XenoPort Forward-Looking Statement

This press release contains "forward-looking" statements, including, without limitation, all statements related to the receipt of future milestone payments under XenoPort’s collaborative agreements and the timing thereof; the timing of future regulatory submissions; and the therapeutic and commercial potential of Solzira. Any statements contained in this press release that are not statements of historical fact may be deemed to be forward-looking statements. Words such as “plans,” “will,” “potential” 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, the ability of the company to successfully conduct the clinical trials for Solzira, and the results thereof; the uncertainty of the FDA approval process and other regulatory requirements; XenoPort' s dependence on its current and additional collaborative partners; and the therapeutic and commercial value of the company' s compounds. 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, 2008, filed with the Securities and Exchange Commission on November 6, 2008. 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 is a registered trademark.

Solzira is a U.S. trademark of GSK.

GSK UK Media enquiries:
Philip Thomson, (020) 8047 5502
Claire Brough, (020) 8047 5502
Alice Hunt, (020) 8047 5502
Gwenan White, (020) 8047 5502
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GSK US Media enquiries:
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Mary Anne Rhyne, (919) 483 2839
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GSK European Analyst/Investor enquiries:
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Sally Ferguson, (020) 8047 5543
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GSK US Analyst/ Investor enquiries:
Tom Curry, (215) 751 5419
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XenoPort Analyst/Investor and Media enquiries:
Jackie Cossmon, (408) 616 7220