FDA Approves Once-Daily Restless Legs Drug: Precursor of Gabapentin (Neurontin)

On April 6, the U.S. Food and Drug Administration approved Horizant™ Extended Release Tablets (gabapentin enacarbil), a once-daily treatment for moderate-to-severe restless legs syndrome (RLS).*

“People with restless legs syndrome can experience considerable distress from their symptoms. Horizant provides significant help in treating these symptoms,” says Russell Katz, MD, director of the Division of Neurology Products in the FDA’s Center for Drug Evaluation and Research.

The effectiveness of the drug was studied in two 12-week clinical trials in adults. The trials showed that people taking the medication had an improvement in their RLS symptoms, compared with people taking an inactive pill (placebo). [Note: patients might want to ask the prescribing physician how much the improvement exceeded placebo results. This information may be reported in the full text of a study reported by researchers at the Stanford (CA) Sleep Medicine Clinic in August 2010.]

Horizant will be dispensed with an FDA-approved Medication Guide that explains the drug’s uses and risks. It may cause drowsiness and dizziness and can impair a person’s ability to drive or operate complex machinery.

The gabapentin enacarbil in Horzant is a precursor compound or “prodrug” of gabapentin – that is, in the body it becomes gabapentin, a drug used under the brand name Neurontin to treat seizures in people with epilepsy (and widely used to relieve neuropathic & other pain, and major depressive disorder).

How Does It Work?

The exact way that gabapentin works has been ill understood. However, new research indicates that the drug – initially synthesized to mimic the chemical structure of the neurotransmitter GABA – may work by halting the formation of new nerve-to-nerve synapses (the junction points where one cell passes electrical or chemical signals to another cell).

Like all drugs used to treat epilepsy, this one carries warnings that they may cause suicidal thoughts and actions in a small number of people. Horizant will have the same warning.

Horizant was developed by GlaxoSmithKline of Research Triangle Park, N.C., and Xenoport of Santa Clara, Calif.
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* RLS is a disorder that causes a strong urge to move the legs. This urge often occurs with unpleasant feelings in the legs. People who have RLS describe feeling pulling, itching, tingling, burning, or aching in their legs, and moving the legs temporarily relieves these feelings. The urge to move often happens when a person is inactive, and the symptoms typically are worse in the evening and early morning.

For information: National Institute of Neurological Disorders and Stroke: Restless Legs Syndrome Information Page.

Source: FDA News Release, Apr 7, 2011

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