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Treatment for Restless Legs Syndrome, Postherpetic Neuralgia

Horizant (gabapentin enacarbil) Now Approved - April 6, 2011

GlaxoSmithKline and XenoPort Respond to FDA on Horizant for RLS

RESEARCH TRIANGLE PARK, N.C. & SANTA CLARA, Calif.--(BUSINESS WIRE)--Nov 5, 2010 - GlaxoSmithKline (NYSE: GSK) and XenoPort, Inc. announced today that the U.S. Food and Drug Administration (FDA) has accepted for review GSK's response to FDA's Complete Response letter for Horizant (gabapentin enacarbil) Extended-Release Tablets. Horizant is under review for the treatment of moderate-to-severe primary Restless Legs Syndrome (RLS).

FDA has designated the resubmission as a Class 2 response and set a new Prescription Drug User Fee Act goal date of April 6, 2011.

Last month, GSK submitted its response to questions raised by FDA in a Complete Response letter dated February 17, 2010. GSK's response to FDA included new data from nonclinical studies of Horizant and two epidemiology studies, conducted by GSK, exploring gabapentin use and cancer based on the UK General Practice Research Database. The resubmission also included a final safety update that provided updated or new safety information on patients in clinical studies who have been treated with Horizant. In order for FDA to be able to consider published gabapentin nonclinical data in their assessment of Horizant, GSK amended the New Drug Application (NDA) for Horizant from a 505(b)(1) to a 505(b)(2) application.

Horizant, also referred to as GSK1838262/XP13512, is a patented new chemical entity. It is an investigational non-dopaminergic treatment for moderate-to-severe primary RLS. It is not approved or marketed anywhere in the world.

The NDA was submitted to FDA on January 9, 2009.

XenoPort 8K Filing

XenoPort is filing a Current Report on Form 8-K with the Securities and Exchange Commission describing the 505(b)(2) regulatory pathway applicable to Horizant in light of a patent listed in the FDA's Orange Book publication for Neurontin.

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

XenoPort 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. Gabapentin enacarbil is also being developed in partnership with Astellas Pharma Inc. for the potential treatment of Restless Legs Syndrome in Japan. XenoPort's product candidates are being evaluated as potential treatments for patients with neuropathic pain, gastroesophageal reflux disease, spasticity and Parkinson's disease. 

Cautionary statement regarding forward-looking statements

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 2009.

XenoPort Forward-Looking Statement

This press release contains "forward-looking" statements, including, without limitation, all statements related to the therapeutic and commercial potential of XenoPort's product candidates and potential future interactions with FDA related to the NDA for Horizant for the treatment of RLS and the 505(b)(2) application process. 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 "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, risks related to the uncertainty of FDA approval process and other regulatory requirements; the 505(b)(2) application process; XenoPort's dependence on its current and additional collaborative partners; the therapeutic and commercial value of the company's compounds; and the risks inherent in patent litigation. 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 June 30, 2010, filed with the Securities and Exchange Commission on August 6, 2010, and in XenoPort's Current Report on Form 8-K, to be filed with the Securities and Exchange Commission on November 8, 2010. 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.

Horizant is a trademark of GSK. XenoPort is a trademark of XenoPort, Inc.

Posted: November 2010

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