An Extension Study to Evaluate the Efficacy and Safety of HORIZANT in Adolescents With Moderate-to-Severe Primary RLS

Inclusion Criteria: Patients who completed participation in HORIZANT Study XP109. * Negative pregnancy test for females of childbearing potential. Male patients able to father a child must agree to use a barrier method (male condom, female condom, diaphragm, or cervical cap) with spermicide for at least 30 days prior to dosing and throughout the study. Fertile, sexually active patients must agree to use 2 medically accepted methods of contraception * Patients must be willing to refrain from using any drugs that are likely to affect RLS or sleep assessments for the duration of the study. * Signed patient and parent (or legal guardian) Institutional Review Board (IRB)-approved assent and consent forms before any study procedures are carried out Exclusion Criteria: * Patients who, in the opinion of the investigator, would be noncompliant with the study visit schedule, procedures, or medication administration * Patients who have developed clinically significant or unstable medical conditions, or who would otherwise be unsuitable for participation in a continuation study with gabapentin enacarbil