Dose-Response and Pharmacokinetics of Gabapentin Enacarbil (GEn [XP13512 / GSK1838262]) in Restless Legs Syndrome (XP081)

A Randomized, Double-Blind, Placebo-Controlled, Dose-Response Study to Assess the Efficacy, Safety, and Pharmacokinetics of XP13512 (GSK1838262) in Patients With Restless Legs Syndrome

The objective of the study was to generate the data necessary to determine the gabapentin exposure produced by 4 dose levels of GEn (600 mg, 1200 mg, 1800 mg, and 2400 mg) or placebo, and the corresponding relief of symptoms in subjects with Restless Legs Syndrome (RLS).

Study Overview

• Status: Completed
• Conditions: Restless Legs Syndrome
• Intervention / Treatment: Drug: GEn (XP13512/GSK1838262); Drug: Placebo

Detailed Description

This was a multicenter, randomized, double blind, placebo controlled, parallel group study, comparing 4 doses of GEn (XP13512) with placebo given once daily to subjects with RLS. Eligible subjects were randomized in equal numbers into 1 of 5 treatment groups (GEn 600 mg, 1200 mg, 1800 mg, or 2400 mg or placebo) for 12 weeks of treatment. Data from this study will be utilized as part of a larger pharmacokinetic (PK) pharmacodynamic (PD) analysis of data from several studies (XP084/RXP111495) that are part of the GEn RLS clinical development program. Safety and tolerability were also assessed.

• Study Type: Interventional
• Enrollment (Actual): 217
• Phase: Phase 2

Contacts and Locations

Study Locations

• United States
  • Texas
    • Dallas, Texas, United States, 75213
      • GSK Investigational Site

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Men or women at least 18 years of age
• RLS, based on the IRLSSG Diagnostic Criteria
• History of RLS symptoms occurring at least 15 nights in the month prior to Screening or, if on RLS treatment, this frequency of symptoms must have been applicable prior to start of treatment
• Documented RLS symptoms for at least 4 of the 7 consecutive evenings/nights
• Total RLS severity score of 15 or greater on the IRLS Rating Scale
• If taking dopamine agonists, gabapentin, or other treatments for RLS (e.g., opioids, benzodiazepines) medications must have been discontinued at least 2 weeks prior to Screening;
• If taking any prescription medication, therapy must have been stabilized for at least 3 months prior to Screening with no anticipated changes for the duration of the study;
• Body Mass Index (BMI) 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
• history of RLS symptom augmentation or end of dose rebound with previous dopamine agonist treatment
• neurologic disease or movement disorder (e.g., diabetic neuropathy, Parkinson's disease, multiple sclerosis, dyskinesias, and dystonias);
• other clinically significant or unstable medical condition or conditions which could affect RLS treatment efficacy assessments
• serum ferritin level below 20 ng/mL
• currently suffering from moderate or severe depression using the Diagnostic and Statistical Manual of Mental Disorders and Treatment IV (DSM IV TR)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

5

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Placebo Comparator: Placebo	Drug: Placebo; Placebo orally once daily
Experimental: GEn (XP13512/GSK1838262) 600 mg	Drug: GEn (XP13512/GSK1838262); Double-Blind Treatment Phase: 600 mg GEn (XP13512) orally, once daily for 3 days followed by 600 or 1200 mg on days 4-6, followed by 600 or 1200 or 1800 mg on days 7-9, followed by 600 or 1200 or 1800 or 2400 mg on days 10-84. Double-Blind Taper Phase: 600 or 1200 or 1800 mg GEn (XP13512) orally, once daily on days 85-86, followed by 600 mg or 1200 mg on days 87-88, followed by 600 mg on days 89-91; Other Names: XP13512; GSK1838262
Experimental: GEn (XP13512/GSK1838262) 1200 mg	Drug: GEn (XP13512/GSK1838262); Double-Blind Treatment Phase: 600 mg GEn (XP13512) orally, once daily for 3 days followed by 600 or 1200 mg on days 4-6, followed by 600 or 1200 or 1800 mg on days 7-9, followed by 600 or 1200 or 1800 or 2400 mg on days 10-84. Double-Blind Taper Phase: 600 or 1200 or 1800 mg GEn (XP13512) orally, once daily on days 85-86, followed by 600 mg or 1200 mg on days 87-88, followed by 600 mg on days 89-91; Other Names: XP13512; GSK1838262
Experimental: GEn (XP13512/GSK1838262) 1800 mg	Drug: GEn (XP13512/GSK1838262); Double-Blind Treatment Phase: 600 mg GEn (XP13512) orally, once daily for 3 days followed by 600 or 1200 mg on days 4-6, followed by 600 or 1200 or 1800 mg on days 7-9, followed by 600 or 1200 or 1800 or 2400 mg on days 10-84. Double-Blind Taper Phase: 600 or 1200 or 1800 mg GEn (XP13512) orally, once daily on days 85-86, followed by 600 mg or 1200 mg on days 87-88, followed by 600 mg on days 89-91; Other Names: XP13512; GSK1838262
Experimental: GEn (XP13512/GSK1838262) 2400 mg	Drug: GEn (XP13512/GSK1838262); Double-Blind Treatment Phase: 600 mg GEn (XP13512) orally, once daily for 3 days followed by 600 or 1200 mg on days 4-6, followed by 600 or 1200 or 1800 mg on days 7-9, followed by 600 or 1200 or 1800 or 2400 mg on days 10-84. Double-Blind Taper Phase: 600 or 1200 or 1800 mg GEn (XP13512) orally, once daily on days 85-86, followed by 600 mg or 1200 mg on days 87-88, followed by 600 mg on days 89-91; Other Names: XP13512; GSK1838262

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Mean Css, Max and Css, Min	Css, max is defined as the maximum or "peak" concentration of a drug observed after multiple administration, at steady state. Css, max is one of the parameters of particular use in estimating the bioavailability of drugs, by measuring the total amount of drug absorbed. Css, min is defined as the minimum concentration of a drug observed after its administration, in steady state. ng, nanograms; PK, pharmacokinetic; W, week; BLQ, below limit of quantitation.	Weeks 4 and 12
Mean Tmax and T1/2	Tmax is defined as the time to the maximum or "peak" concentration of a drug observed after multiple administration. T1/2 is defined as the time to when half of the total amount of a particular substance is eliminated from the body.	Weeks 4 and 12
Mean AUCss	The area under the plot of plasma concentration of drug against time after drug administration is defined as the area under the curve (AUC). The AUCss is the area under the curve during the steady-state period. The AUCss is of particular use in estimating the bioavailability of drugs, by measuring the extent of absorption. AUCss used concentration data from 0 to 24 hours at steady-state for Weeks 4 and 12.	Weeks 4 and 12

Collaborators and Investigators

• Sponsor: XenoPort, Inc.

Publications and helpful links

General Publications

• Ahmed M, Hays R, Steven Poceta J, Jaros MJ, Kim R, Shang G. Effect of Gabapentin Enacarbil on Individual Items of the International Restless Legs Study Group Rating Scale and Post-sleep Questionnaire in Adults with Moderate-to-Severe Primary Restless Legs Syndrome: Pooled Analysis of 3 Randomized Trials. Clin Ther. 2016 Jul;38(7):1726-1737.e1. doi: 10.1016/j.clinthera.2016.05.008. Epub 2016 Jun 7.
• Avidan AY, Lee D, Park M, Jaros MJ, Shang G, Kim R. The Effect of Gabapentin Enacarbil on Quality of Life and Mood Outcomes in a Pooled Population of Adult Patients with Moderate-to-Severe Primary Restless Legs Syndrome. CNS Drugs. 2016 Apr;30(4):305-16. doi: 10.1007/s40263-016-0329-4.
• Ondo WG, Hermanowicz N, Borreguero DG, Jaros MJ, Kim R, Shang G. Effect of prior exposure to dopamine agonists on treatment with gabapentin enacarbil in adults with moderate-to-severe primary restless legs syndrome: pooled analyses from 3 randomized trials. J Clin Mov Disord. 2015 Mar 30;2:9. doi: 10.1186/s40734-015-0018-3. eCollection 2015.
• Lal R, Ellenbogen A, Chen D, Zomorodi K, Atluri H, Luo W, Tovera J, Hurt J, Bonzo D, Lassauzet ML, Vu A, Cundy KC. A randomized, double-blind, placebo-controlled, dose-response study to assess the pharmacokinetics, efficacy, and safety of gabapentin enacarbil in subjects with restless legs syndrome. Clin Neuropharmacol. 2012 Jul-Aug;35(4):165-73. doi: 10.1097/WNF.0b013e318259eac8.

Study record dates

Study Major Dates

• Study Start: January 1, 2007
• Primary Completion (Actual): January 1, 2008
• Study Completion (Actual): January 1, 2008

Study Registration Dates

• First Submitted: April 7, 2011
• First Submitted That Met QC Criteria: April 7, 2011
• First Posted (Estimate): April 11, 2011

Study Record Updates

• Last Update Posted (Estimate): July 22, 2013
• Last Update Submitted That Met QC Criteria: July 15, 2013
• Last Verified: May 1, 2011

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Mental Disorders; Pathologic Processes; Nervous System Diseases; Sleep Disorders, Intrinsic; Dyssomnias; Sleep Wake Disorders; Neurologic Manifestations; Neurobehavioral Manifestations; Disease; Dyskinesias; Psychomotor Disorders; Parasomnias; Syndrome; Psychomotor Agitation; Restless Legs Syndrome
• Other Study ID Numbers: 111462