XP13512 is a transported prodrug of gabapentin, a drug that has been sold by Pfizer as Neurontin since 1993 and is currently sold as a generic drug by a number of companies.
The phase IIa clinical trial was a randomized, double-blind, placebo-controlled, multicenter study to assess the safety, tolerability, pharmacokinetics and efficacy of XP13512 in patients with post-herpetic neuralgia (PHN).
The primary endpoint for the clinical trial was the change in average pain score between the seven days of baseline assessment to the final seven days of XP13512 or placebo treatment using an 11-point numerical pain scale. Compared to placebo, treatment with XP13512 was associated with a statistically significant reduction in pain as measured by this pain scale.
Statistically significant improvements in pain were also observed using the short-form McGill pain questionnaire. Additionally, XP13512 treatment was associated with a statistically significant reduction in sleep interference when compared to placebo and the clinical benefit of XP13512 over placebo was supported by observed statistically significant improvements in both patient and investigator global impression of change.
XP13512 is designed to be actively transported from the gastrointestinal tract into the bloodstream, where it is metabolized to produce gabapentin. A daily dose of 2,400mg of XP13512 has the potential to release 1,248mg of gabapentin into the bloodstream, which equates to approximately two-thirds the daily dose administered during the Neurontin treatment period. Nevertheless, XP13512 produced on average a 17% increase in the steady-state average blood concentration of gabapentin compared to that produced by Neurontin dosing.
“We are delighted with the results of this trial demonstrating the efficacy of twice-a-day XP13512 in managing PHN,” said Dr Ronald Barrett, XenoPort’s CEO.
“We are particularly gratified to see that the pharmacokinetic advantages of XP13512 over Neurontin observed in phase I clinical trials with healthy subjects were confirmed in PHN patients. We are also intrigued by the improvement in pain that was observed when patients were switched from Neurontin to XP13512 in this clinical trial.”