GlaxoSmithKline and XenoPort announced that the FDA has approved Horizant (gabapentin enacarbil extended-release tablets) for the treatment of moderate-to-severe primary Restless Legs Syndrome (RLS) in adults. This approval was based on data from two 12-week clinical trials enrolling more than 400 patients. Approximately 75% of patients treated with Horizant for 12 weeks said their symptoms were much or very much improved, compared with about 45% of those taking placebo.

Horizant is a prodrug of 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 RLS is unknown. Horizant is not interchangeable with other gabapentin products because of differing pharmacokinetic profiles.

Horizant is expected to be available July 1, 2011 in a 600mg dosage strength.

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