GlaxoSmithKline and XenoPort, Inc. announced that the US 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, MD, 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, MD, senior vice president, GlaxoSmithKline Neurosciences Medicine Development Centre. “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.”

Horizant is a new chemical entity discovered and developed by XenoPort, 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 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, PhD, XenoPort’s chief executive officer.  “XenoPort is honoured 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.”

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 has 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. Horizant is a prodrug of gabapentin, an Anti-Epileptic Drug (AED). AEDs increase the risk of suicidal thoughts or behaviour in patients taking these drugs for any indication.

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 US and/or western European populations. Key diagnostic criteria 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.

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 nutrient transport mechanisms to improve the therapeutic benefits of existing drugs.