XP13512 (GSK1838262) Versus Placebo in Patients With Restless Legs Syndrome.

Inclusion Criteria:

• Patients with primary RLS, based on the International RLS Study Group Diagnostic Criteria.
• History of RLS symptoms at least 15 nights in the prior month or, if on treatment, this frequency of symptoms before treatment was started;
• Documented RLS symptoms for at least 4 of the 7 consecutive evenings/nights during the Baseline study period;
• Total RLS severity score of 15 or greater on the International Restless Legs Syndrome Study Group Rating Scale (IRLS rating scale) at Visit 1 and at Visit 2;
• Discontinuation of dopamine agonists and/or gabapentin at least 2 weeks prior to Baseline;
• Discontinuation of other treatments for RLS (e.g., opioids, benzodiazepines) at least 2 weeks prior to Baseline;
• If female of child-bearing potential, the subject must agree to use clinically accepted birth control through completion of the study;
• Body Mass Index of 34 or below;
• Estimated creatinine clearance of at least 60 mL/min;

Exclusion Criteria:

• A sleep disorder (e.g., sleep apnea) that may significantly affect the assessment of RLS;
• Neurologic disease or movement disorder (e.g., diabetic neuropathy, Parkinson's Disease, Multiple Sclerosis, dyskinesias, and dystonias);
• Abnormal laboratory results, electrocardiogram (ECG) or physical findings;
• Pregnant or lactating women;
• Women of childbearing potential who are not practicing an acceptable method of birth control.