Friday, GlaxoSmithKline (NYSE:GSK) and XenoPort, Inc. (NASDAQ:XNPT) announced top-line results from a Phase II-b clinical trial. The study evaluates the safety and efficacy of GSK1838262/XP13512 (gabapentin enacarbil) for neuropathic pain, associated with post-herpetic neuralgia (PHN) in adults.

The company reported that subjects were randomized to receive placebo, 1200, 2400 or 3600 mg/day of GSK1838262 dosed twice a day; all patients treated with GSK1838262 demonstrated statistically significant improvements over the control group. The primary endpoint was the change from baseline to the end of maintenance treatment in the 24-hour average pain intensity score. The 14-week, double-blind study enrolled 376 subjects with PHN who experienced pain for at least three months following healing of the herpes zoster skin rash.

Overall, GSK1838262 was well tolerated at all doses in this study. The most common adverse events were dizziness (placebo 15%, 1200 mg/day 17%, 2400 mg/day 26% and 3600 mg/day 30%) and somnolence (8%, 10%, 11% and 14%, respectively). Many of these symptoms were mild or moderate in intensity. Withdrawals due to adverse events were 13%, 6%, 15% and 18% for the respective dosage groups.

Atul Pande, M.D., senior vict president at GlaxoSmithKline, commented, “We are encouraged by the positive results in this study of GSK1838262 in treating neuropathic pain associated with PHN, which is a debilitating condition for affected patients. We look forward to sharing the full results at a future medical meeting. We are currently evaluating the next steps for the development of this compound for the treatment of neuropathic pain.”

Chief Executive Officer of XenoPort, Ronald W. Barrett, Ph.D., added, “We are pleased with the efficacy and tolerability results observed across all doses in this study. These results build upon the positive Phase II-a study in PHN patients we previously conducted with this product candidate. We look forward to continuing to work with GSK to advance the development of this compound in neuropathic pain.”