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FDA Approves Horizant for Postherpetic Neuralgia

GSK and XenoPort Receive FDA Approval for Horizant for Postherpetic Neuralgia

LONDON & RESEARCH TRIANGLE PARK, N.C. & SANTA CLARA, Calif.--(BUSINESS WIRE)--Jun 7, 2012 - GlaxoSmithKline plc and XenoPort, Inc. announced today that the United States (US) Food and Drug Administration (FDA) has approved Horizant (gabapentin enacarbil) Extended-Release Tablets for the management of postherpetic neuralgia (PHN) in adults.

The efficacy and safety of Horizant for the management of PHN was evaluated in a single 12-week principal efficacy trial, plus two supportive studies that all met their respective primary endpoints. The three clinical studies involved 574 adult patients from the US, Canada and Germany.

The recommended dosage for the management of PHN in adults is 600 mg twice daily. Treatment should be initiated at a dose of 600 mg in the morning for three days followed by 600 mg twice daily (1,200 mg/day) beginning on day four. Doses must be adjusted in patients with impaired renal function. In the 12-week, controlled study in patients with PHN, somnolence and dizziness were the most frequently reported side effects. Somnolence was reported in 10% of patients treated with 1,200 mg of Horizant per day compared with 8% of patients receiving placebo. Dizziness was reported in 17% of patients receiving 1,200 mg of Horizant per day compared with 15% of patients receiving placebo.

In association with GSK's first commercial sale of the product after approval for PHN, XenoPort is entitled to a milestone payment of $10 million from GSK.

About Horizant

Horizant is not approved or licensed outside the US for PHN. It was approved for the treatment of moderate-to-severe primary Restless Legs Syndrome (RLS) in adults in the US on 6th April 2011. It is not recommended for RLS patients who need to sleep during the day and remain awake at night. Please see Important Safety Information below and the complete prescribing information available at www.gsk.com.

Discovered and developed by XenoPort, gabapentin enacarbil utilizes the body's nutrient transport mechanisms that are believed to facilitate its absorption into the body. Once absorbed, it is converted into gabapentin, which binds to a specific type of calcium channel but does not exhibit affinity for other common receptors. The exact mechanism of action of the compound in treating RLS or managing the symptoms of PHN is unknown.

Horizant is not interchangeable with other gabapentin products because of differing pharmacokinetic profiles. The same dose of Horizant results in different plasma concentrations of gabapentin relative to the same dose of other gabapentin products.

Important Safety Information for Horizant (gabapentin enacarbil)

Effects on Driving

Somnolence/Sedation and Dizziness

Lack of Interchangeability With Gabapentin

Suicidal Behavior and Ideation

Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity

Discontinuation of Horizant

Adverse Reactions

About Postherpetic Neuralgia

Postherpetic neuralgia is a neuropathic (nerve) pain syndrome that may result in disability in some people. PHN follows the healing of an outbreak of herpes zoster, commonly known as shingles. Approximately one million people in the US develop shingles each year. Of these, approximately ten percent develop PHN.

About GlaxoSmithKline

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. For further information please visit www.gsk.com.

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. Horizant is XenoPort's first FDA-approved product. GSK holds commercialization rights and certain development rights for Horizant in the US. Regnite® (gabapentin enacarbil) Extended-Release Tablets is approved for the treatment of RLS 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 and has co-promotion and certain development rights to gabapentin enacarbil in the US. XenoPort's pipeline of product candidates includes potential treatments for patients with spasticity and Parkinson's disease. To learn more about XenoPort, please visit the Web site at www.XenoPort.com.

Horizant is a registered US trademark of GSK. XENOPORT is a registered trademark of XenoPort, Inc. Regnite is a registered trademark of Astellas.

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 2011.

Registered in England & Wales:

No. 3888792

Registered Office: 980 Great West Road

Brentford, Middlesex

TW8 9GS

Contact: GlaxoSmithKline Enquiries:
UK Media enquiries:
David Mawdsley, +44 (0) 20 8047 5502 (London)
Stephen Rea, +44 (0) 20 8047 5502 (London)
Sarah Spencer, +44 (0) 20 8047 5502 (London)
David Daley, +44 (0) 20 8047 5502 (London)
or
US Media enquiries:
Bradd Pavur, +1-919-483-0044 (North Carolina)
Holly Russell, +1-919-483-2954 (North Carolina)
or
Analyst/Investor enquiries:
Sally Ferguson, +44 (0) 20 8047 5543 (London)
Tom Curry, + 1-215-751-5419 (Philadelphia)
Gary Davies, + 44 (0) 20 8047 5503 (London)
Jeff McLaughlin, + 1-215-751-7002 (Philadelphia)
Ziba Shamsi, + 44 (0) 20 8047 3289 (London)
or
XenoPort Enquiries:
XenoPort Analyst/Investor and Media enquiries:
Jackie Cossmon, + 1-408-616-7220

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