GlaxoSmithKline and XenoPort receive FDA approval for Horizant™

Issued: London, UK, Research Triangle Park, NC & Santa Clara, CA

• New treatment for moderate-to-severe primary Restless Legs Syndrome

GlaxoSmithKline (NYSE: GSK) and XenoPort, Inc. (Nasdaq: XNPT) announced Wednesday that the U.S. Food and Drug Administration (FDA) has approved Horizant™ (gabapentin enacarbil) Extended-Release Tablets for the treatment of moderate-to-severe primary Restless Legs Syndrome in adults.  Horizant is not recommended for patients who are required to sleep during the daytime and remain awake at night. The efficacy of Horizant in the treatment of patients with moderate-to-severe primary Restless Legs Syndrome was demonstrated in two 12-week clinical trials in adults. It is the first medication in its class to be approved for the treatment of moderate-to-severe primary Restless Legs Syndrome.

“Clinical experience has substantiated that Restless Legs Syndrome, also referred to as Ekbom Disease, is a long-term neurological condition characterized by an urge to move caused by unpleasant sensations in the legs,” said Richard K. Bogan, M.D., FCCP, chairman and chief medical officer of SleepMed of South Carolina in Columbia, South Carolina, and a clinical trial investigator.  “Our experience has shown that patients with moderate-to-severe primary Restless Legs Syndrome can suffer from a range of disruptive symptoms and may benefit from a new treatment option.”

“Restless Legs Syndrome remains under-recognized, and many patients go untreated as a result,” said Atul Pande, M.D., senior vice president, GlaxoSmithKlineNeurosciencesMedicineDevelopmentCenter.  “GSK has been committed to helping patients and healthcare professionals better understand and treat this condition.   We are pleased to provide a new treatment for moderate-to-severe primary Restless Legs Syndrome.”

Discovered and developed by XenoPort, Horizant is a new chemical entity that utilizes the body’s nutrient transport mechanisms that are believed to facilitate its absorption into the body.  Once absorbed, Horizant 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 Horizant in treating moderate-to-severe primary Restless Legs Syndrome 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.

“This significant milestone represents the culmination of XenoPort’s efforts to develop a non-dopaminergic therapy for patients with Restless Legs Syndrome,” said Ronald W. Barrett, Ph.D., XenoPort’s chief executive officer.  “XenoPort is honored to have contributed to the efforts to find new treatments for Restless Legs Syndrome, and we hope that we can continue to develop other important medicines that can provide meaningful treatment benefit to sufferers of central nervous system disorders.” 

IMPORTANT SAFETY INFORMATION about Horizant (gabapentin enacarbil)

The recommended dosage of Horizant (gabapentin enacarbil) is 600 mg once daily taken with food at about 5:00 pm.  A daily dose of 1,200 mg provided no additional benefit compared with the 600-mg dose, but caused an increase in adverse reactions.

Gabapentin enacarbil causes significant driving impairment.  Patients being treated with gabapentin enacarbil should not drive until they have gained sufficient experience to assess whether gabapentin enacarbil impairs their ability to drive.  However, prescribers and patients should be aware that patients’ ability to assess their own driving competence, as well as their ability to assess the degree of somnolence caused by gabapentin enacarbil, can be imperfect.

Gabapentin enacarbil causes somnolence/sedation and dizziness.  Patients should be advised not to drive a car or operate other complex machinery until they have gained sufficient experience on gabapentin enacarbil to assess whether gabapentin enacarbil impairs their ability to perform these tasks.  

Gabapentin enacarbil is a prodrug of gabapentin, an antiepileptic drug (AED).  AEDs increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication.  Because Horizant is a prodrug of gabapentin, gabapentin enacarbil also increases this risk.  Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.

When discontinuinggabapentin enacarbil, patients receiving the recommended dose of 600 mg daily can discontinue the drug without tapering.  If the recommended dose is exceeded, the dose should be reduced to 600 mg daily for one week prior to discontinuation to minimize the potential of withdrawal seizure.

The dose of gabapentin enacarbil should be adjusted in subjects with renal impairment (creatinine clearance 30 to 59 mL/min); gabapentin enacarbil 600 mg should be administered on Day 1, Day 3, and every day thereafter.  Gabapentin enacarbil is not recommended in patients with creatinine clearance less than 30 mL/min or in patients on hemodialysis.

In three 12-week clinical trials, the two most commonly observed adverse reactions for gabapentin enacarbil 600 mg per day (n=163), gabapentin enacarbil 1200 mg per day (n=269), and placebo (n=245), respectively, were somnolence/sedation (20%, 27%, and 6%) and dizziness (13%, 22%, and 4%).

Please see full Prescribing Information and Medication Guide available at www.gsk.com.

About Restless Legs Syndrome (also known as Ekbom Disease)

Restless Legs Syndrome is a neurological disorder characterized by an urge to move the legs usually caused or accompanied by uncomfortable and unpleasant sensations in the legs.  Estimates of the prevalence for Restless Legs Syndrome in adult patients with medically-significant symptoms ranged between 1.5% to 2.7% in U.S. and/or western European populations.^1,2,3,4  Key diagnostic criteria for Restless Legs Syndrome are:   an urge to move the legs usually accompanied or caused by uncomfortable and unpleasant leg sensations, symptoms begin or worsen during periods of rest or inactivity such as lying or sitting, symptoms are partially or totally relieved by movement such as walking or stretching at least as long as the activity continues, and symptoms are worse or occur only in the evening or night. Studies have identified potential gene variants associated with Restless Legs Syndrome. Research in this area is ongoing.

Conference Call and Webcast Information

XenoPort will host a conference call at 9:00 a.m. Eastern Time tomorrow to discuss the approval of Horizant for moderate-to-severe primary Restless Legs Syndrome.  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 1-706-679-1417.

The replay of the conference call may be accessed after 12:00 p.m. Eastern Time tomorrow via the Internet at www.XenoPort.com, or via phone at 1-800-642-1687 for domestic callers or 1-706-645-9291 for international callers.  The reference number to enter both the call and replay of the call is 58624319.

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.

XenoPort is a biopharmaceutical company focused on developing a portfolio of internally discovered product candidates that utilize the body’s nutrient transport mechanisms to improve the therapeutic benefits of existing drugs.  Horizantis XenoPort’s first approved product.  GlaxoSmithKline holds commercialization rights and certain development rights for gabapentin enacarbil in the United States.  Gabapentin enacarbil is also being developed in partnership with Astellas Pharma Inc. for the potential treatment of Restless Legs Syndrome in Japan.  If approved in Japan, gabapentin enacarbil would be marketed under a different trade name.  XenoPort holds all other world-wide rights and has co-promotion and certain development rights to gabapentin enacarbil in the United States.  XenoPort’s pipeline of product candidates includes potential treatments for patients with neuropathic pain, spasticity and Parkinson’s disease.  XenoPort’s product candidates were discovered and developed by XenoPort utilizing its patented Transported Prodrug™ technology.  Except for gabapentin enacarbil, XenoPort owns rights to all of its product candidates.  To learn more about XenoPort, please visit the Web site at www.XenoPort.com.

Editor’s Note: This product was formerly referred to as XP13512, GSK1838262 and the proposed trade name Solzira™.

Horizant™ is a trademark of GSK.  XenoPort and Transported Prodrug are trademarks of XenoPort, Inc.   

GlaxoSmithKline 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 2010.

XenoPort Forward-Looking Statements

This press release contains "forward-looking" statements, including, without limitation, all statements related to the therapeutic and commercial potential of Horizant; XenoPort’s and its partners’ future clinical development and commercialization of gabapentin enacarbil; Japanese regulatory processes; and future product development by XenoPort.  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 “can,” “hope,” “may,” "potential," “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 and GSK’s ability to successfully co-promote Horizant in the United States; the ability of XenoPort to successfully conduct clinical trials of its product candidates, and the results thereof; the uncertainty of the Japanese regulatory approval processes and other regulatory requirements; and XenoPort' s dependence on its current and additional collaborative partners. These and other risk factors are discussed under the heading "Risk Factors " in XenoPort' s Annual Report on Form 10-K for the year ended December 31, 2010, filed with the Securities and Exchange Commission on March 1, 2011. 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.

References

1. Allen RP, Bharmal M, Calloway M. Prevalence and disease burden of primary restless legs syndrome: results of a general population survey in the United States. Movement Disorders 2011;26:114–120.
2. Allen RP, Stillman P, Myers AJ. Physician-diagnosed restless legs syndrome in a large sample of primary medical care patients in Western Europe: prevalence and characteristics. Sleep Med 2010;11:31-37.
3. Allen RP, Walters AS, Montplaisir J, et al. Restless legs syndrome prevalence and impact: REST general population study. Arch Intern Med 2005;165:1286-1292.
4. Hening W, Walters AS, Allen RP, et al. Impact, diagnosis and treatment of restless legs syndrome (RLS) in a primary care population: The REST (RLS Epidemiology, Symptoms and Treatment) primary care study. Sleep 2004; 5:237-246.