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

Patients who complete the 12-week daily dosing efficacy and safety study (XP109) will be
allowed to enroll in the open-label extension (OLE) study (XP110), thereby providing exposure
to HORIZANT for up to 48 weeks. Enrolled patients will take open-label HORIZANT 600 mg
tablets once a day at approximately 5 PM with food, beginning at Week 0 of the OLE study up
to and including Week 36. After the end of the treatment period, a follow-up visit will be
included 14 days (± 3 days) after the last dose of HORIZANT. Patients will visit the clinical
site on 6 different occasions, including a follow-up visit 14 days (± 3 days) after the last
dose of study drug.

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