Valeant Pharmaceuticals International (NYSE: VRX) today announced preliminary results from its Phase IIa proof-of-concept clinical trial of retigabine for the treatment of pain associated with postherpetic neuralgia (PHN), a painful and common complication of shingles. While retigabine was generally well tolerated, the study did not meet its pre-specified primary efficacy endpoint. Further detailed analyses are warranted and are ongoing.
"As is typical in many proof-of-concept studies, these results are inconclusive at this time with regard to the potential utility of retigabine in PHN patients," stated J. Michael Pearson, chairman and chief executive officer. "The treatment duration was relatively short and with limited statistical powering for the study overall. There are many additional analyses that have yet to be undertaken and these will be performed over the next several months. Moreover, given that the provisional results from this study will not impact the submission of our New Drug Application for retigabine in epilepsy, we remain focused on the submission as our number one priority."
The study was a randomized, double-blind, placebo-controlled Phase IIa proof-of-concept study with 187 patients randomized 2:1 of retigabine versus placebo for a treatment period of up to 10 weeks. The study was conducted in approximately 50 trial locations. Study patients were titrated to their individually determined maximum tolerated dose within the range of 300 mg to 900 mg per day. The primary outcome assessment was the comparison of the average pain intensity over the last seven days of maintenance therapy with retigabine versus placebo. Pain intensity was measured on a standard 0 - 10 numerical rating scale.
PHN is a painful complication of Herpes Zoster, a condition commonly known as "shingles." Shingles results from a reactivation of the Varicella Zoster virus, the same agent that causes chicken pox. Patients with shingles typically have a painful blistering rash that lasts for several weeks. PHN occurs when nerve fibers are damaged during an outbreak of shingles, causing chronic and often excruciating pain that may continue for months or years. Currently available treatments for PHN include topical medications, over-the-counter analgesics, tricyclic antidepressants and antiepileptics.
Retigabine, a first-in-class neuronal potassium channel opener, is currently in late-stage development as an adjunctive treatment for patients with partial-onset seizures. In Phase III epilepsy trials, retigabine was shown to be efficacious with a demonstrated reduction in monthly seizure rates.