Drug major GlaxoSmithKline plc (GSK) and biopharmaceutical firm XenoPort, Inc. (XNPT) announced Wednesday the U.S. Food and Drug Administration approval for Horizant (gabapentin enacarbil) extended-release tablets for the treatment of moderate-to-severe primary Restless Legs Syndrome in adults. The news sent XenoPort stock soaring nearly 57 percent in after-hours trading.
Horizant is the first medication in its class to be approved for the treatment of moderate-to-severe primary Restless Legs Syndrome, or RLS, and is also Santa Clara, California-based XenoPort's first approved product which it has discovered and developed.
Horizant is a modified version of gabapentin, an epilepsy drug that has been sold by Pfizer, Inc. (PFE) as Neurontin since 1993 and is currently sold as a generic drug by a number of companies.
For Horizant , this is its second go-around with the FDA. Last February, Horizant was issued a complete response letter in which the FDA indicated that a preclinical finding of pancreatic acinar cell tumors in rats was of sufficient concern to preclude approval of Horizant for RLS at that time.
U.K.-based GlaxoSmithKline holds commercialization rights and certain development rights for gabapentin enacarbil in the U.S. Gabapentin enacarbil is also being developed in partnership with Astellas Pharma, Inc. (ALPMY.PK) for the potential treatment of RLS in Japan.
In December 2005, XenoPort licensed rights to develop and commercialize Horizant to Astellas Pharma, Inc. (ALPMY.PK) in Japan and five Asian countries, and licensed the rights to GlaxoSmithKline in the U.S. and all other regions of the world in February 2007.
Last November, XenoPort reacquired all rights to Horizant outside of the U.S. that were previously granted to GlaxoSmithKline (which excludes the Astellas territory).
RLS, also known as Ekbom Disease, is a neurological disorder characterized by an urge to move the legs usually caused or accompanied by uncomfortable and unpleasant sensations in the legs such as creeping, crawling, pulling, itching, tingling or burning sensations.
According to the National Institute of Neurological Disorders and Stroke, as many as 10 percent of the U.S. population may have RLS. About 2-3 percent of adults (more than 5 million individuals) are said to have moderate to severe RLS. An additional 5 percent appears to be affected by a milder form.
Horizant is also being evaluated by GlaxoSmithKline for the potential treatment of post-herpetic neuralgia, or PHN, a chronic type of neuropathic pain that can follow the resolution of shingles, and Horizant has successfully completed several Phase 2 clinical trials for the management of PHN in the U.S.
In addition, GlaxoSmithKline evaluated Horizant for the potential treatment of diabetic peripheral neuropathy, or DPN, and as a potential prophylactic therapy for migraine headaches. However, Horizant did not show statistically significant separation from placebo in the primary endpoints of these trials.
XNPT closed Wednesday's regular trading session at $6.38, down $0.36 or 5.34 percent on a volume of 2.48 million shares. However, the stock soared $3.62 or 56.74 percent in after-hours trading. Meanwhile, GSK closed at $39.72, up $0.10 or 0.25 percent on a volume of 1.99 million shares.
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