GlaxoSmithKline and XenoPort, Inc. achieved positive results from a Phase II trial evaluating GSK1838262/XP13512 (gabapentin enacarbil) in patients with neuropathic pain associated with post-herpetic neuralgia (PHN), who have had an inadequate response to gabapentin. In this double-blind, two-period cross-over study, 3600 mg/day of GSK1838262 demonstrated a statistically significant improvement over 1200 mg/day of GSK1838262 on the primary endpoint, which was the change from baseline to the end of the treatment period in the 24-hour average pain intensity score.

This study enrolled 138 subjects with PHN who had been experiencing pain for at least three months following healing of the herpes zoster skin rash. Subjects with a history of inadequate response to gabapentin received a dose of 1800 mg/day of gabapentin for two weeks. Subjects who had a 24-hour average pain score of at least four on the 11-point pain intensity rating scale were then randomized to receive either 1200 mg/day of GSK1838262 for the first treatment period followed by 3600 mg/day for the second treatment period, or 3600 mg/day followed by 1200 mg/day. Subjects received 2400 mg/day of GSK1838262 for four days in between the two treatment periods.

“These results from another positive study of GSK1838262 in the treatment of PHN will be important as we evaluate our next steps in the development program for neuropathic pain,” said Atul Pande, M.D., senior vice president, GlaxoSmithKline Neurosciences Medicines Development Center.

“Clinical trial experience has shown that there are PHN patients who do not experience adequate pain relief,” said Ronald W. Barrett, Ph.D., chief executive officer of XenoPort. “We are encouraged by these Phase II results and plan to share further details about the study at a future medical meeting.”