GlaxoSmithKline and XenoPort have reported encouraging top-line results from the last Phase III clinical trial of XP13512 for the treatment of moderate-to-severe restless legs syndrome.

Up to 12 million people in the USA are thought to suffer with RLS, which is characterised by unpleasant and sometimes painful sensations in the legs that result in a compelling urge to move. Because symptoms typically occur at night, RLS patients often suffer from sleep disruption.

XP13512 is a novel prodrug of gabapentin (Pfizer’s anti-epileptic Neurontin) that utilises high-capacity transport mechanisms in the gastrointestinal tract to improve absorption, and is “the first non-dopaminergic agent to demonstrate efficacy in controlled clinical trials for the treatment of primary RLS,” said Atul Pande, senior vice president, GlaxoSmithKline Neurosciences Medicines Development Center.

Safe and effective
According to the firms, this latest 325-patient, 12-week trial showed that the drug is able to induce statistically-significant improvements in the symptoms of the condition compared to placebo, and it was also found to be generally well tolerated.

“With three positive pivotal RLS trials now completed, we hope to provide an important new treatment option to patients with primary RLS,” commented Ronald Barrett, chief executive of XenoPort, and the groups confirmed their intention to file a New Drug Application in the third quarter of 2008.