The Effect of Horizant (Gabapentin Enacarbil) on Augmentation (XP-IIT-0034)

To Examine the Effect of Horizant (Gabapentin Enacarbil) in Primary Restless Legs Syndrome (RLS) Patients Who Are on Dopaminergic Agents and Exhibiting Augmentation

Restless Legs Syndrome (RLS) is a common neurological disorder. Augmentation is the main complication during long-term DA treatment of RLS. This study aims to examine effect of Horizant (Gabapentin Enacarbil) on Augmentation in RLS patients.

This is an Open label single arm study. The purpose of the study is to demonstrate the efficacy of Horizant in patients with RLS who exhibit augmentation while on Dopaminergic therapy. Adult patients (age 18-85 years) with diagnosis of primary RLS (diagnosed by study investigators) with augmentation on dopaminergic therapy will be screened for participation in the study. RLS diagnosis will be made by the study investigators using International RLS study group criteria. Patients with augmentation on dopaminergic therapy as defined by NIH 2007 with ASRS of 5 to 15 will be offered to participate in the study. Inclusion and exclusion criteria are listed below. The study will be performed after approval of the Institutional Review Board of the University of Missouri. A total of 50 subjects will be entered into the study over a period of 1 year. Written consent will be obtained from all patients. After pre-participation evaluation for eligibility, subjects will be selected and enrolled in the study and followed for a total of 6 follow up visits (Days 0, 30, 90, 120, 180, 360). Subjects Enrollment period will last up to 12 months. The total duration of study will be 24 months.

Phase1: During phase 1 therapy, Horizant will be added on as an adjunct to all subjects taking part in the study along with stable dose of their current dopaminergic (DA) agent and both medication will be continued for a total period of 90 days from day 0 to day 90. Subjects will be evaluated for three visits (days 0, 30 and 90) during Phase I. Phase 2: At the 90th day follow-up visit, with initiation of phase 2 therapy, all subjects will be tapered off (by 50% reduction in dose each week) of their current dopaminergic agents while maintaining the same dose of Horizant and will be on Horizant monotherapy. All subjects will be evaluated for additional three clinic visits (days 120, 180, 360).

Change in Augmentation Severity Rating Scale Form Day 0 to Day 360 (270 Days After Discontinuation pf Dopaminergic Medication)

Numeric Scale to assess degree of augmentation; Range 0-24; 0 is better, 24 is worst. We compared the Augmentation severity scale on day 0 to day 360 (which is 270 days after this decrease of dopaminergic medication)

Inclusion Criteria: Adult patients with diagnosis of RLS for more than one year. Patients who are on DA therapy for 6 months or longer. Patients who developed Augmentation (on stable dose of DA) lasting for 3 months or longer. Augmentation severity rating scale of 5 to 15. Both males and females Age range = 18-85 year Exclusion Criteria: Known Hypersensitivity to Horizant or Gabapentin products Peripheral neuropathy Radiculopathy Peripheral vascular disease Uremia [abnormal blood urea nitrogen (BUN) or Creatinine on Comprehensive Metabolic Panel (CMP)] Anemia Patients who are currently pregnant Patients who currently take opioids, lithium, anti-nausea medications (e.g. metoclopramide), dopaminergic antagonists (e.g. Haloperidol), 1st generation antihistamines (e.g. diphenhydramine, pseudoephedrine), anti-psychotic medications and iron therapy. Subjects with impaired decision making capability.