The Food and Drug Administration (FDA) approved a new drug, Horizant Extended Release Tablets, on Wednesday to treat moderate to severe primary Restless Legs Syndrome in adults.  Horizant is a patented new chemical entity discovered and developed by both GlaxoSmithKline and XenoPort.

Restless Legs Syndrome affects up to 10 percent of the U.S. population and is a disorder of the nervous system that causes an urge in the body to move one’s legs.  This disorder is classified as a sleeping disorder because it affects and interferes with a person’s sleeping habits.  The irresistible need to move one’s legs in attempt to relieve the sensations is often described as uncomfortable, “pins and needles,” or a “creepy crawly” feeling.  The sensations are often made worse when laying down, sitting or when legs are trying to rest.

“People with Restless Legs Syndrome can experience considerable distress from their symptoms,” Russell Katz, MD, director of the division of neurology products in the FDA’s Center for Drug Evaluation and Research, states in an FDA news release.  “Horizant provides significant help in treating these symptoms.”

The drug was approved based on two studies that were done in more than 2,300 adults.  These 12-week studies showed improvement in Restless Legs Syndrome patients trying Horizant that was considerably greater than those patients who were receiving a placebo.  Patients received oral daily doses in a range from 600 to 3,600 mg.

According to the full Prescribing Information provided on Horizant’s website, the recommended doze of this drug is 600 mg once daily taken with food.  The drug is not to be cut, crushed or chewed. Horizant is a prodrug of gabapentin and is described as an acetic acid.  It’s molecular formula is C16H27NO6.

This drug is administered orally and contains 600 mg of gabapentin enacarbil and the following other inactive ingredients: colloidal silicon dioxide, dibasic calcium phosphate dihydrate, glyceryl behenate, magnesium sterate, sodium lauryl sulfate, and talc.

The FDA states that Horizant “may cause drowsiness and dizziness and can impair a person’s ability to drive or operate complex machinery.”  Horizant’s website also confirms that this drug causes significant driving impairment.  It is an antiseizure medicine, and like all drugs of this type, Horizant holds a warning label about the risk of suicidal thoughts and actions in a small number of people.

According to a news release from GlaxoSmithKilne and XenoPort, do not take Horizant if you sleep during the daytime and remain awake at night.

This is a significant milestone in XenoPort and GlaxoSmithKline’s efforts to develop a non-dopaminergic therapy.  “We hope that we can continue to develop other important medicines that can provide meaningful treatment benefit to sufferers of central nervous system disorders,” Ronald Barett, CEO of XenoPort said.

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About the author

Dana Consalvo