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, GlaxoSmithKline Neurosciences Medicine Development Center. “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.