UPDATE 1-XenoPort says pain drug meets main goal of trial

* Neuropathic pain drug meets main goal of mid-stage trial

* XenoPort shares jump 29 pct

Sept 17 (Reuters) - Biopharmaceutical company XenoPort Inc (XNPT.O) and its partner GlaxoSmithKline Plc (GSK.L) (GSK.N) said their neuropathic pain drug met the main goal of reducing the intensity of pain in a mid-stage trial.

Shares of XenoPort surged as much as 29 percent, before paring some gains to trade up $5.30 at $25 Thursday morning. The stock was the second biggest percentage gainer on Nasdaq. GlaxoSmithKline was trading flat at $38.93 on the New York Stock Exchange.

The companies said the drug, XP13512 or GSK1838262, reduced the intensity of pain compared with a dummy drug, and was well tolerated at all doses in the study.

The drug is being studied to treat adults with post-herpetic neuralgia, a neuropathic pain syndrome that usually follows an outbreak of shingles -- an infection of a nerve and the area of skin supplied by the nerve -- and mostly affects people over fifty years. (Reporting by Anuradha Ramanathan in Bangalore; Editing by Deepak Kannan) ((anuradha.ramanathan@thomsonreuters.com; within U.S. +1 646 223 8780; outside U.S. +91 80 4135 5800: Reuters Messaging: anuradha.ramanathan.reuters.com@reuters.net))