A Clinical Study in Subjects With Neuropathic Pain From PHN Who Have Had an Inadequate Response to Gabapentin Treatment

The purpose of this study is evaluate the difference between two doses of gabapentin enacarbil (XP13512/GSK1838262), hereafter referred to as GEn, on pain associated with post-herpetic neuralgia.

The primary purpose of study PXN110527 was to investigate the efficacy of a high (3600mg/day) dose versus a low (1200mg/day) dose of GEn in subjects with post-herpetic neuralgia (PHN) who have a history of an inadequate response to gabapentin treatment. The study is a cross-over design. Prior to screening subjects are required to have a demonstrated history of an inadequate response (as determined by the investigator) to at least 1800 mg/day of gabapentin. Prior history of treatment with gabapentin includes current treatment at 1800mg/day (2 weeks) or prior treatment with ≥1800mg/day (4 weeks). Subjects could also have been treated with pregabalin monotherapy (150-300mg/day, ≥4 weeks) and had an inadequate response. Subjects are treated with gabapentin 1800mg/day during the Baseline Period and are randomized if during the Basleline Period they are compliant with gabapentin treatment and have a 24-hour average pain intensity score ≥4.0 based on an 11-point pain intensity numerical rating scale (PI-NRS). Subjects are then randomized to receive gabapentin enacarbil (either 1200mg/day or 3600mg/day in a 1:1 ratio) for Treatment Period 1 (28 days). Followed by a dose of 2400mg/day for 4 days and the alternate fixed dose (either 3600 mg/day or 1200 mg/day) for Treatment Period 2 (28 days).