GlaxoSmithKline and XenoPort's migraine prophylaxis drug fails in Ph II testing, sending latter's share plunging

UK drug giant GlaxoSmithKline says that its GSK1838262/XP13512 (gabapentin enacarbil), which is under development with originator USA-based XenoPort, did not demonstrate a statistically-significant improvement compared to placebo as a prophylactic treatment for migraine headaches.

The disappointing news saw XenoPort's shares ' which have already lost 75% of their value since hitting a 52 week high of $25.42 last September - slump 26% to $6.53 in early trading yesterday, though it had little impact on GSK.

This Phase II dose-ranging study evaluated the efficacy, safety and tolerability of GSK1838262 in adults diagnosed with migraine headache (with or without aura) according to the International Headache Society criteria. The 30-week, double-blind, placebo-controlled study randomized 526 patients to receive 1,200, 1,800, 2,400 or 3,000mg/day of GSK1838262 or placebo, administered twice daily. The primary efficacy endpoint was the change from baseline in the number of migraine headache days during the last four weeks of treatment prior to taper. GSK1838262 did not demonstrate a statistically significant improvement over placebo on the primary endpoint. The failure of the study may be a consequence of the unexpectedly high placebo response rate observed.