A potential treatment for restless leg syndrome (RLS) shows effectiveness in a Phase III clinical trial, British drugmaker GloxoSmithKline and its developmental partner, California Company XenoPort reported on Tuesday.

People suffering from RLS face disturbing, 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. According to the National Institutes of Health, the condition is estimated to affect up to 12 million people in the U.S. Data suggest that RLS can have an impact on quality of life that is equal to or worse than major chronic disorders such as diabetes and osteoarthritis.

According to the companies, the 327 patients diagnosed with moderate-to-severe primary RLS who participated in the study were administered the experimental drug code-named XP-13512 over the course of 24 weeks.

Only 9 percent of patients who took XP-13512 experienced worsening symptoms versus 23 percent of those taking placebo. The drug also was shown to be legally well-tolerated after nine months of treatment.

“The results of this study strengthen our belief that XP13512 has the potential to be a safe and effective treatment for primary RLS. Our first placebo-controlled Phase 3 efficacy trial of XP13512, with results announced in April 2007, demonstrated statistically significant benefits of XP13512 in treating RLS symptoms over 12 weeks. We are encouraged that XP13512 treatment was associated with a statistically significant difference from placebo in this randomized withdrawal study, particularly in light of the stringent criteria for relapse used in this clinical trial. We are also pleased with the tolerability profile of XP13512 in this nine-month study,” said XenoPort Chief Executive Ronald W. Barrett.

He added that final 12-week Phase III results will be reported later this quarter and he expects Glaxo to file a new drug application with the Food and drug Administration for XP13512 in the third quarter of 2008.

Shares of Glaxo fell 35 cents to $52.40 in morning trade, while XenoPort's stock fell $3.12, or 5.1 percent, to $58.