A randomized, double-blind, placebo-controlled study to assess the efficacy and tolerability of gabapentin enacarbil in subjects with restless legs syndrome

A comprehensive update on the ADMET considerations for α2δ calcium channel ligand medications for treating restless legs syndrome

INTRODUCTION

Restless legs syndrome/Willis-Ekbom disease (RLS/WED) is a sleep-related sensory-motor disorder associated with poor sleep quality and impaired daily functioning. In patients affected by chronic RLS/WED, a pharmacological therapy is recommended. International guidelines suggest to start the treatment with a α2δ calcium channel ligand in most cases, unless contraindicated.

AREAS COVERED

The present review is based on an extensive Internet and PubMed search from 1986 to 2024. Our purpose is to describe the absorption, distribution, metabolism, and toxicology (ADMET) of the α2δ ligands, with common consideration for the therapeutic class, specificities of different compounds, efficacy, and safety in relation to other treatment options.

EXPERT OPINION

α2δ ligands are quite similar in their ADMET profiles, sharing most of the pharmacokinetics and potential adverse effects. However, we highlight the linear kinetic of gabapentin enacarbil and pregabalin, differently from gabapentin. α2δ ligands are safe and effective for the treatment of RLS/WED. Additional benefits can be obtained in comorbid insomnia, chronic pain syndromes, history of impulse control disorder, and comorbid anxiety. The use of α2δ ligands is associated with poor risk of augmentation. We still need new long-term safe and effective treatments, which could be developed along with our knowledge of RLS/WED pathophysiology.

Efficacy and safety of tonic motor activation (TOMAC) for medication-refractory restless legs syndrome: a randomized clinical trial

STUDY OBJECTIVES

The purpose of this study was to evaluate the efficacy and safety/tolerability of bilateral high-frequency tonic motor activation (TOMAC) in patients with medication-refractory restless legs syndrome (RLS).

METHODS

RESTFUL was a multicenter, randomized, double-blind, sham-controlled trial in adults with medication-refractory moderate-to-severe primary RLS. Participants were randomized 1:1 to active or sham TOMAC for a double-blind, 4-week stage 1 and all received active TOMAC during open-label, 4-week stage 2. The primary endpoint was the Clinical Global Impressions-Improvement (CGI-I) responder rate at the end of stage 1. Key secondary endpoints included change to International RLS Study Group (IRLS) total score from study entry to the end of stage 1.

RESULTS

A total of 133 participants were enrolled. CGI-I responder rate at the end of stage 1 was significantly greater for the active versus sham group (45% vs. 16%; Difference = 28%; 95% CI 14% to 43%; p = .00011). At the end of stage 2, CGI-I responder rate further increased to 61% for the active group. IRLS change at the end of stage 1 improved for the active versus sham group (-7.2 vs. -3.8; difference = -3.4; 95% CI -1.4 to -5.4; p = .00093). There were no severe or serious device-related adverse events (AEs). The most common AEs were mild discomfort and mild administration site irritation which resolved rapidly and reduced in prevalence over time.

CONCLUSIONS

TOMAC was safe, well tolerated, and reduced symptoms of RLS in medication-refractory patients. TOMAC is a promising new treatment for this population.

CLINICAL TRIAL

Noninvasive Peripheral Nerve Stimulation for Medication-Refractory Primary RLS (The RESTFUL Study); clinicaltrials.gov/ct2/show/NCT04874155; Registered at ClinicalTrials.gov with the identifier number NCT04874155.

"Unvoluntary" Movement Disorders: Distinguishing between Tics, Akathisia, Restless Legs, and Stereotypies

Tics, stereotypies, akathisia, and restless legs fall at different places on the spectrum of discrete, unwanted and potentially disabling motor routines. Unlike tremor, chorea, myoclonus, or dystonia, this subgroup of abnormal movements is characterized by the subject's variable ability to inhibit or release undesired motor patterns on demand. Though it may be sometimes clinically challenging, it is crucial to distinguish these "unvoluntary" motor behaviors because secondary causes and management approaches differ substantially. To this end, physicians must consider the degree of repetitiveness of the movements, the existence of volitional control, and the association with sensory symptoms, or cognitive-ideational antecedent. This review aims to summarize the current existing knowledge on phenomenology, diagnosis, and treatment of tics, stereotypies, akathisia, and restless leg syndrome.

Effects of Gabapentin and Pregabalin on Calcium Homeostasis: Implications for Physical Rehabilitation of Musculoskeletal Tissues

PURPOSE OF REVIEW

In this review, we discuss the mechanism of action of gabapentinoids and the potential consequences of long-term treatment with these drugs on the musculoskeletal system.

RECENT FINDINGS

Gabapentinoids, such as gabapentin (GBP) and pregabalin (PGB) were designed as antiepileptic reagents and are now commonly used as first-line treatment for neuropathic pain and increasingly prescribed off-label for other pain disorders such as migraines and back pain. GBP and PGB exert their analgesic actions by selectively binding the α₂δ₁ auxiliary subunit of voltage-sensitive calcium channels, thereby inhibiting channel function. Numerous tissues express the α₂δ₁ subunit where GBP and PGB can alter calcium-mediated signaling events. In tissues such as bone, muscle, and cartilage, α₂δ₁ has important roles in skeletal formation, mechanosensation, and normal tissue function/repair that may be affected by chronic use of gabapentinoids. Long-term use of gabapentinoids is associated with detrimental musculoskeletal outcomes, including increased fracture risk. Therefore, understanding potential complications is essential for clinicians to guide appropriate treatments.

Difference in background factors between responders to gabapentin enacarbil treatment and responders to placebo: pooled analyses of two randomized, double-blind, placebo-controlled studies in Japanese patients with restless legs syndrome

OBJECTIVE

Restless legs syndrome (RLS) is a sensorimotor disorder that is characterized by uncomfortable and unpleasant sensations mainly in the legs. Two placebo-controlled studies (Phase II/III and post-marketing) in Japanese patients with RLS failed to demonstrate the efficacy of gabapentin enacarbil (GE) 600 mg in the change from baseline in International Restless Legs Syndrome Rating Scale (IRLS) score at the end of the treatment period. The high response to placebo is thought to be a possible reason why the post-marketing study failed. The objectives of these post hoc analyses were to determine potential predictive factors associated with improvement in IRLS score with GE treatment and to identify subgroups with higher placebo responses.

METHODS

We combined data from the two Japanese studies and analyzed change from baseline in IRLS score in the pooled population and subgroups defined by several patient characteristics. Moreover, we calculated the variable importance of each factor and performed predictive enrichment analysis to identify an enrichable subpopulation with greater improvement by GE treatment.

RESULTS

The post hoc analyses suggested that higher baseline IRLS score (≥21) and higher body mass index (≥25 kg/m²) were associated with higher placebo responses. On the other hand, positive family history of RLS, prior use of dopaminergic receptor agonists, and higher baseline ferritin level (≥50 ng/mL) were associated with higher responses to GE.

CONCLUSIONS

Our results suggest that patients with typical idiopathic RLS characteristics, including positive family history and no low ferritin level, would be expected to derive the greatest benefits from GE treatment.

Sleep Disturbance, Sleep Disorders and Co-Morbidities in the Care of the Older Person

Sleep complaints can be both common and complex in the older patient. Their consideration is an important aspect of holistic care, and may have an impact on quality of life, mortality, falls and disease risk. Sleep assessment should form part of the comprehensive geriatric assessment. If sleep disturbance is brought to light, consideration of sleep disorders, co-morbidity and medication management should form part of a multifaceted approach. Appreciation of the bi-directional relationship and complex interplay between co-morbidity and sleep in older patients is an important element of patient care. This article provides a brief overview of sleep disturbance and sleep disorders in older patients, in addition to their association with specific co-morbidities including depression, heart failure, respiratory disorders, gastro-oesophageal reflux disease, nocturia, pain, Parkinson's disease, dementia, polypharmacy and falls. A potential systematic multidomain approach to assessment and management is outlined, with an emphasis on non-pharmacological treatment where possible.

[Restless legs syndrome]

Restless legs syndrome (RLS) is seen widely in clinical practice. RLS commonly occurs at night time and presents with unpleasant or uncomfortable sensations in the legs that causes an urge to move them. This article describes the epidemiology, risk factors and pathophysiology of RLS. There is a detailed description of clinical presentations, diagnostic criteria and also management of RLS.

Pharmacologic Treatment of Restless Legs Syndrome

Restless legs syndrome (RLS)/Willis-Ekbom disease is a neurologic disorder characterized by a strong desire to move when at rest (usually in the evening) and paraesthesia in their lower legs. The most widely used therapies for first-line treatment of RLS are dopaminergic drugs; however, their long-term use can lead to augmentation. α2δ Ligands, opioids, iron, glutamatergic drugs, adenosine, and sleep aids have been investigated as alternatives. The pathogenesis of RLS is not well understood. Despite the efficacy of dopaminergic drugs in the treatment of this disorder, unlike in Parkinson’s disease dopaminergic cell loss in the substantia nigra has not been observed in RLS. The etiology of RLS is likely complex, involving multiple neural pathways. RLS-related genes identified in genome-wide association studies can provide insight into the mechanistic basis and pathophysiology of RLS. Here we review the current treatments and knowledge of the mechanisms underlying RLS.

Nighttime Agitation and Restless Legs Syndrome in Persons With Alzheimer's Disease: Study Protocol for a Double-Blind, Placebo-Controlled, Randomized Trial (NightRest)

Nighttime agitation is a prevalent symptom in persons with Alzheimer's disease (AD). Effective treatments are absent due to our limited knowledge of its etiology. We hypothesized that restless legs syndrome (RLS), a common neurological sensorimotor disorder of uncomfortable leg sensations that appear at night and interfere with sleep, might be a cause for nighttime agitation in persons with AD. RLS is infrequently identified in persons with AD because traditional diagnosis is dependent on patients answering complex questions about their symptoms. With a validated observational tool for RLS diagnosis, the Behavioral Indicators Test-Restless Legs, we aim to diagnose RLS and determine the effect of gabapentin enacarbil (GEn) compared to placebo on nighttime agitation, sleep, antipsychotic medications, and the mechanism for these effects. We hypothesize that frequency of RLS behaviors will mediate the relationship between GEn and nighttime agitation. This study is an 8-week, double-blind, placebo-controlled, randomized pilot clinical trial, followed by an 8-week open-label trial, that is being conducted in long-term care settings and private homes. The results of this study may shift, personalize, and improve standards of care for treatment of nighttime agitation; reduce aggression and other nighttime agitation behaviors; and improve sleep.

TARGETS

Persons with AD with nighttime agitation potentially caused by RLS.

INTERVENTION DESCRIPTION

Diagnose RLS and determine the effect of GEn.

MECHANISMS OF ACTION

The frequency of RLS behaviors will mediate the relationship between GEn and nighttime agitation.

OUTCOMES

Determine the effect of GEn on nighttime agitation, sleep, and antipsychotic medications.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03082755 (Date of registration March 6, 2017). [Research in Gerontological Nursing, 13(6), 280-288.].

Symptoms of Restless Legs Syndrome in A Palliative Care Population: Frequency and Impact

Objectives: We hypothesized that restless legs syndrome (RLS) would be common and associated with impaired quality of life (QOL) among palliative care outpatients. Methods: 76 palliative care clinic patients completed the National Institutes of Health restless legs syndrome (NIH-RLS) screening questionnaire. Questionnaire data was also gathered on RLS severity and RLS-related QOL, and the Short Form Health Survey (SF-12) was used to measure QOL. Analysis was performed for associations between RLS categorization and QOL measures. Results: 31 patients (40.8 percent) met criteria for RLS. RLS-positive patients had moderate-to-severe RLS symptoms and impaired RLS-specific QOL. RLS-positive patients scored lower on the mental component of the SF–12 (39 ± 11 versus 45 ± 12, p=0.03), though not on the physical component. In a multivariate regression analysis, higher levels of RLS severity had 2-point lower SF-12 mental component scores compared to lower levels of RLS severity (p=0.04), with no difference in physical component scores (p=0.47). Conclusion: RLS appears common in palliative care outpatients and is associated with impairments in QOL.

Restless Legs Syndrome and Other Movement Disorders of Sleep-Treatment Update

PURPOSE OF REVIEW

The purpose of this review article is to summarize and discuss the recent advances in the treatment of restless legs syndrome (RLS), as well as REM sleep behavior disorder (RBD), and periodic leg movement disorder (PLMD).

RECENT FINDINGS

Traditionally, dopaminergic therapy has been considered the sole option for first-line treatment of RLS due to their impressive acute efficacy. Dopamine agonists such as oral pramipexole and ropinirole, as well as transdermal rotigotine are all effective treatment options. However, augmentation of the RLS symptoms is a major limitation of oral dopaminergic therapy. Recently, gabapentinoid agents such as gabapentin enacarbil and pregabalin have shown comparable short-term efficacy to dopaminergics with lower risk of augmentation of the RLS symptoms. Recent evidence on the efficacy of oxycodone-naloxone in treatment-resistant RLS provides an additional therapeutic avenue. The increasing understanding of the role of iron in RLS pathophysiology has led to new options in iron supplementation therapy in RLS, including treatment with ferric carboxymaltose. With emerging evidence of augmentation being a side effect specific to dopaminergic treatment, gabapentinoids are considered a safer option as initial treatment. In severe refractory RLS, oxycodone-naloxone can be used. If iron stores are low, IV iron formulations should be the initial treatment choice. New treatment options are needed to address issues with current therapies.

Differential Diagnosis and Treatment of Restless Legs Syndrome: A Literature Review

Restless legs syndrome (RLS) is a chronic neurological disorder affecting a growing number of people. Patients describe an irresistible urge to move their lower limbs in times of immobility. Due to its vague symptoms and similarity to other disorders, it has become increasingly difficult for primary care clinicians to properly diagnose and manage RLS. As a result, patients with RLS are routinely misdiagnosed and continue their lives without proper management. This literature review examines the current understanding of the disorder, provides key points to assist clinicians in differentiating RLS from similar disorders, and explores recently updated evidence-based guidelines for the effective management of RLS.

Disturbances of Sleep and Alertness in Parkinson's Disease

PURPOSE OF REVIEW

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Sleep dysfunction is one of the most common non-motor manifestations of PD that has gained significant interest over the past two decades due to its impact on the daily lives of PD patients, poorly understood mechanisms, and limited treatment options. In this review, we discuss the most common sleep disorders in PD and present recent investigations that have broadened our understanding of the epidemiology, clinical manifestations, diagnosis, and treatment of disturbed sleep and alertness in PD.

RESENT FINDINGS

The etiology of impaired sleep-wake cycles in PD is multifactorial. Sleep dysfunction in PD encompasses insomnia, REM sleep behavior disorder, sleep-disordered breathing, restless legs syndrome, and circadian dysregulation. Despite the high prevalence of sleep dysfunction in PD, evidence supporting the efficacy of treatment strategies is limited. We are at the opportune time to advance our understanding of sleep dysfunction in PD, which will hopefully lead to mechanisms-driven interventions for better sleep and allow us to approach sleep as a modifiable therapeutic target for other non-motor and motor manifestations in PD.

Use of α2δ Ligands for Restless Legs Syndrome/Willis Ekbom Disease

Restless legs syndrome is a common neurological condition affecting a substantial portion of the population. It can be an idiopathic disorder, or one that is secondary to another cause. Given that the underlying pathophysiology of restless legs syndrome is not well understood, several drug classes have been studied for symptom control. While dopamine agonists have long been the mainstay of first-line treatment for restless legs syndrome, recently, the α2δ ligands have been increasingly used. These agents have proven both efficacious and safe in a number of clinical trials. Additionally, compared with the dopamine agonists, they have been associated with less augmentation, a phenomenon whereby symptoms emerge earlier in the day, become more severe, and may spread to areas of the body previously unaffected. Newer clinical guidelines for restless legs syndrome are increasingly recommending the α2δ ligands as a logical first-choice medication for patients needing drug therapy for symptom control.

Pharmacological Management of Restless Legs Syndrome and Periodic Limb Movement Disorder in Children

Restless legs syndrome (RLS) and periodic limb movement disorder (PLMD) are under-recognized sleep disorders in children and adolescents. Several recent epidemiological studies have shown that RLS and PLMD are common in the pediatric population, and if left untreated, may lead to cardiovascular and neurocognitive consequences. Therefore, early diagnosis and intervention may help preventing long-term consequences. The management of RLS and PLMD in children involves both non-pharmacologic and pharmacologic approaches. Although there is emerging literature supporting medical therapy in children with RLS and PLMD, the overall experiences with these medications remain limited. Most children and adolescents with RLS and PLMD have low iron storage; therefore, iron therapy should be considered as the first line of treatment in children. Currently, there is no FDA-approved medication for RLS and PLMD in children. There is increasing evidence on the effectiveness of dopaminergic medications in children but the data are quite limited. Other medications such as α2δ-1 ligands, benzodiazepine, and clonidine are frequently used, but have not been adequately investigated in children. Further studies are needed to evaluate the safety and efficacy of pharmacologic therapy for RLS and PLMD in children.

Identification and treatment of augmentation in patients with restless legs syndrome: practical recommendations

Restless legs syndrome (RLS) is a chronic disorder causing clinically significant discomfort to approximately 3% of adults. Although RLS was first identified centuries ago, our understanding of this disorder, its causes, and its treatments is still evolving. In particular, our knowledge of the potential negative effects of RLS treatments, including dopaminergic augmentation, continues to expand. Augmentation, which refers to a paradoxical treatment-related increase in RLS symptoms, has been associated with all three dopamine agonists approved for the treatment of RLS - rotigotine, pramipexole, and ropinirole. This review presents key information on prevention and treatment of dopaminergic augmentation from the recently published consensus-based guidelines issued by the International RLS Study Group task force in conjunction with the European RLS Study Group and the RLS Foundation for first-line treatment of RLS/Willis-Ekbom disease. If dopamine agonists are used to treat RLS, it is recommended that the dosage should be kept as low as possible without exceeding the maximum dose recommended for RLS treatment. As the frequency of augmentation with the rotigotine patch may only be slightly lower than that associated with pramipexole or ropinirole, medications that are effective and have little risk of augmentation, such as alpha-2-delta ligands, may be considered for initial RLS treatment. In addition, we present our clinical experience with treating patients with dopaminergic augmentation by highlighting 2 case studies and practical considerations when treating different patient populations. Applying current RLS augmentation diagnosis and treatment guidelines, as well as collecting detailed histories of worsening RLS symptoms, is critical for patient safety and effective management of RLS augmentation.

Efficacy and Tolerability of Gabapentin in Adults with Sleep Disturbance in Medical Illness: A Systematic Review and Meta-analysis

BACKGROUND AND PURPOSE

The aim of this study was to systematically review the efficacy and tolerability of gabapentin in the treatment of sleep disturbance in patients with medical illness.

METHODS

PubMed was searched for randomized, double-blinded, placebo-controlled trials that reported sleep changes during gabapentin treatment up to November 2015.

FINDINGS

This review included 26 studies involving 4,684 participants. Except for Composite Endpoint 3 [standardized mean difference (SMD) = 0.09, 95% confidence interval (CI): -0.05-0.22] compared with the placebo group, the gabapentin group showed superior outcomes on our endpoints: Composite Endpoint 1 (SMD = 0.50, 95% CI: 0.28-0.71), Composite Endpoint 2 (SMD = -0.53, 95% CI: -0.77 to -0.30), Composite Endpoint 4 (SMD = -0.38, 95% CI: -0.58 to -0.19), Composite Endpoint 5 [risk ratio (RR) = 1.79, 95% CI: 1.24-2.58], and Composite Endpoint 6 (RR = 0.48, 95% CI: 0.32-0.72). However, the patients in the gabapentin group showed worse tolerance than those in the placebo group (RR = 1.38, 95% CI: 1.08-1.76).

IMPLICATIONS

This study is the first to systematically assess the clinical value of gabapentin for the treatment of sleep disorders. We found that regardless the type of sleep outcomes, gabapentin displayed stable treatment efficacy for sleep disturbance in patients with medical illness. However, when an average dose of approximately 1,800 mg/day was used, the risk of treatment discontinuation or drug withdrawal was relatively high. We recommend that further studies confirm these findings in patients with primary sleep disorders.

SLEEP AND CIRCADIAN RHYTHM DISORDERS IN PARKINSON'S DISEASE

Purpose of review

Sleep disorders are among the most challenging non-motor features of Parkinson's disease (PD) and significantly affect quality of life. Research in this field has gained recent interest among clinicians and scientists and is rapidly evolving. This review is dedicated to sleep and circadian dysfunction associated with PD.

Recent findings

Most primary sleep disorders may co-exist with PD; majority of these disorders have unique features when expressed in the PD population.

Summary

We discuss the specific considerations related to the common sleep problems in Parkinson's disease including insomnia, rapid eye movement sleep behavior disorder, restless legs syndrome, sleep disordered breathing, excessive daytime sleepiness and circadian rhythm disorders. Within each of these sleep disorders, we present updated definitions, epidemiology, etiology, diagnosis, clinical implications and management. Furthermore, areas of potential interest for further research are outlined.

Gabapentin Enacarbil: A Review in Restless Legs Syndrome

Gabapentin enacarbil is an extended-release prodrug of gabapentin that is approved in the USA (Horizant(®)) and Japan (Regnite(®)) for the treatment of moderate to severe primary restless legs syndrome (RLS) in adults [featured indication]. This article summarizes pharmacological, efficacy and tolerability data relevant to the use of oral gabapentin enacarbil in this indication. In double-blind, multicentre trials, treatment with gabapentin enacarbil 600 mg/day for 12 weeks significantly improved the symptoms of moderate to severe primary RLS in adults. Gabapentin enacarbil also significantly improved RLS pain scores and generally improved sleep and mood outcomes. These data are supported by retrospective pooled analyses of three of these trials (XP081, PIVOT RLS I and PIVOT RLS II), with gabapentin enacarbil generally improving symptoms irrespective of disease severity, associated sleep disturbance or prior dopamine agonist use. Responses to gabapentin enacarbil were sustained in longer-term trials, with lower relapse rates in gabapentin enacarbil than placebo recipients in a longer-term maintenance study. Overall, in short and longer-term trials, relatively few patients discontinued treatment, adverse events were mostly mild to moderate in severity, and somnolence/sedation and dizziness were the most commonly reported adverse events. Notably, there were no reports of augmentation or QT-interval prolongation. Gabapentin enacarbil is an important agent for the treatment of adults with moderate to severe primary RLS.

Practice guideline summary: Treatment of restless legs syndrome in adults: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

OBJECTIVE

To make evidence-based recommendations regarding restless legs syndrome (RLS) management in adults.

METHODS

Articles were classified per the 2004 American Academy of Neurology evidence rating scheme. Recommendations were tied to evidence strength.

RESULTS AND RECOMMENDATIONS

In moderate to severe primary RLS, clinicians should consider prescribing medication to reduce RLS symptoms. Strong evidence supports pramipexole, rotigotine, cabergoline, and gabapentin enacarbil use (Level A); moderate evidence supports ropinirole, pregabalin, and IV ferric carboxymaltose use (Level B). Clinicians may consider prescribing levodopa (Level C). Few head-to-head comparisons exist to suggest agents preferentially. Cabergoline is rarely used (cardiac valvulopathy risks). Augmentation risks with dopaminergic agents should be considered. When treating periodic limb movements of sleep, clinicians should consider prescribing ropinirole (Level A) or pramipexole, rotigotine, cabergoline, or pregabalin (Level B). For subjective sleep measures, clinicians should consider prescribing cabergoline or gabapentin enacarbil (Level A), or ropinirole, pramipexole, rotigotine, or pregabalin (Level B). For patients failing other treatments for RLS symptoms, clinicians may consider prescribing prolonged-release oxycodone/naloxone where available (Level C). In patients with RLS with ferritin ≤75 μg/L, clinicians should consider prescribing ferrous sulfate with vitamin C (Level B). When nonpharmacologic approaches are desired, clinicians should consider prescribing pneumatic compression (Level B) and may consider prescribing near-infrared spectroscopy or transcranial magnetic stimulation (Level C). Clinicians may consider prescribing vibrating pads to improve subjective sleep (Level C). In patients on hemodialysis with secondary RLS, clinicians should consider prescribing vitamin C and E supplementation (Level B) and may consider prescribing ropinirole, levodopa, or exercise (Level C).

Incidence of Augmentation in Primary Restless Legs Syndrome Patients May Not Be That High: Evidence From A Systematic Review and Meta-Analysis

Augmentation is a common complication of primary restless legs syndrome (RLS) during treatment; however, its incidence rate remains unclear.The aim of this study is investigate the rate of augmentation during RLS treatment.We searched 6 databases, including PubMed, OVID, Embase, Wiley citations, Web of Science research platform (including SciELO Citation Index, Medline, KCI Korean Journal Database, the Web of Science™ Core Collection), and the Cochrane library, and screened the reference lists of the included trials and recently published reviews.Randomized controlled trials and observational studies that reported augmentation events during RLS treatment.Primary RLS patients older than 18 years.No restrictions regarding intervention types were applied.Three investigators independently extracted and pooled the data to analyze the augmentation rate of the total sample and of patient subgroups with different interventions, treatment durations and drug regimens and different geographic origins. Fixed-effects or random-effects model was used for pooled analysis.A total of 60 studies involving 11,543 participants suggested an overall augmentation rate of 5.6% (95% confidence intervals (CI), 4.0-7.7). The augmentation incidence was 6.1% (95% CI, 4.1-9.1) for long-term treatment and 3.3% (95% CI, 1.4-7.3) for short-term treatment. In addition, 27.1% (95% CI, 12.3-49.5) of the levodopa-treated patients, 6.0% (95% CI, 4.1-8.8) of the patients treated with dopamine agonists, and 0.9% (95% CI, 0.2-3.3) of the patients taking pregabalin or gabapentin developed augmentation. Augmentation occurred in 7.2% (95% CI, 5.0-10.3) of the patients taking immediate-release drugs and in 1.7% (95% CI, 0.6-5.0) of the patients taking transdermal application.The main limitations are that the augmentation rates were not evaluated according to drug dosage, gender, and age and symptom severity.Approximately 5 to 6 in 100 RLS patients developed augmentation during treatment.

Modified-Release Formulations of Second-Generation Antiepileptic Drugs: Pharmacokinetic and Clinical Aspects

Modified-release or extended-release (XR) formulations are used to decrease the frequency of dosing for drugs with rapid elimination, to improve convenience and adherence. Use of a modified-release formulation can decrease the peak to trough fluctuations in serum concentrations and theoretically improve the therapeutic benefit of the drug, by decreasing adverse events associated with the higher peak concentrations. Once-daily formulations of lamotrigine (Lamictal XR(®)), levetiracetam (Keppra XR(®)), oxcarbazepine (Oxtellar XR(®), Apydan(®) extent) and topiramate (Qudexy XR™, Trokendi XR™) are approved for the treatment of focal and/or generalized onset seizures. Other seizure medications have been approved for non-epileptic symptoms. Gabapentin XR (Gralise(®)) is approved for the treatment of post-herpetic neuralgias. Gabapentin enacarbil XR (Horizant(®)) is a prodrug of gabapentin and is indicated for treatment of post-herpetic neuralgia and restless leg syndrome, a novel indication. For all but Qudexy XR™, the tablets/capsules must be swallowed whole, without cutting, crushing or chewing, in order to maintain the XR properties of the formulation. Qudexy XR™ can be swallowed intact or the capsules can be opened and sprinkled onto soft food for those with swallowing difficulties, for example, children and the elderly. The bioavailability of Gralise(®) and Horizant(®) is significantly affected by food, specifically fat content, and should be taken with a meal to maximize absorption. Overall, the primary advantage of the newly released XR formulations is the once-daily dosing to improve convenience and adherence, with very limited data suggesting improved tolerability.

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

Background

Dopamine agonists (DAs) are a first-line therapy for moderate-to-severe restless legs syndrome (RLS), but these treatments may lead to complications, such as augmentation and impulse control disorders, requiring switching to another therapeutic class. Here we assess efficacy and tolerability of gabapentin enacarbil (GEn) in adults with moderate-to-severe primary RLS, with or without prior DA exposure.

Methods

Data from 3 trials were pooled. Patients were identified as DA-naive or DA-exposed, based on prior treatment with ropinirole, pramipexole, rotigotine, or pergolide mesylate, and the dopamine precursor levodopa. Details on prior treatment duration and dose were unavailable. Patients with a history of augmentation were excluded. Within DA-naive/DA-exposed patients we investigated the co-primary end points from the pivotal trials: mean change from baseline to week 12 in International RLS (IRLS) Rating Scale total score and proportion of responders (“much”/“very much” improved) on the investigator-rated Clinical Global Impression–Improvement (CGI-I) scale. Safety was also assessed.

Results

671 patients were randomized (DA-naive: placebo, n = 194; GEn 600 mg, n = 131; GEn 1200 mg, n = 214; DA-exposed: placebo, n = 50; GEn 600 mg, n = 30; GEn 1200 mg, n = 52). Across treatment arms, no significant differences between DA-naive and DA-exposed subgroups in IRLS Rating Scale total score change from baseline at any visit were seen, except week 1 in the placebo group (−6.1 DA-naive vs −3.4 DA-exposed, P = .020). No significant differences in the odds of CGI-I response at week 12 between DA-naive vs DA-exposed patients in any treatment group were seen; however, with placebo there was a nonsignificant trend toward fewer responders among DA-exposed (34.0%) vs DA-naive (44.3%) patients. Both GEn doses significantly improved the IRLS Rating Scale total score change from baseline and CGI-I response vs placebo, regardless of prior DA exposure. The most common treatment-emergent adverse events were dizziness and somnolence.

Conclusions

Prior DA exposure had no significant effect on efficacy or tolerability of GEn (600 or 1200 mg) in this pooled analysis of adults with moderate-to-severe primary RLS. These data support the use of GEn in DA-exposed and DA-naive patients.

Trial registration

ClinicalTrials.gov NCT00298623, NCT00365352, and NCT01332305

Recommendations of the Sleep Study Group of the Italian Dementia Research Association (SINDem) on clinical assessment and management of sleep disorders in individuals with mild cognitive impairment and dementia: a clinical review

Clinical assessment and management of sleep disturbances in patients with mild cognitive impairment and dementia has important clinical and social implications. Poor sleep results in an increased risk of morbidities and mortality in demented patients and is a source of stress for caregivers. Sleep disturbances show high prevalence in mild cognitive impairment and dementia patients and they are often associated one to another in the same patient. A careful clinical evaluation of sleep disorders should be performed routinely in the clinical setting of individuals with cognitive decline. The Sleep Study Group of the Italian Dementia Research Association (SINDem) reviewed evidence from original research articles, meta-analyses and systematic reviews published up to December 2013. The evidence was classified in quality levels (I, II, III) and strength of recommendations (A, B, C, D, E). Where there was a lack of evidence, but clear consensus, good practice points were provided. These recommendations may not be appropriate for all circumstances and should therefore be adopted only after a patient's individual characteristics have been carefully evaluated.

Restless legs syndrome and pregnancy: a review

Restless legs syndrome (RLS) is a common sensorimotor neurological disorder that is diagnosed according to the revised criteria of the International RLS Study Group (IRLSSG). The pathophysiology of RLS is still unknown and its prevalence is influenced by ethnicity, age, and gender. RLS is divided into two types by etiology: primary or idiopathic and secondary. Primary RLS is strongly influenced by a genetic component while secondary RLS is caused by other associated conditions such as end-stage renal disease or peripheral neuropathy. Another common condition associated with RLS is pregnancy. The prevalence of RLS during pregnancy is two to three times higher than in the normal population and is influenced by the trimester and the number of parity. The main mechanisms that may contribute to the pathophysiology of RLS during pregnancy are hormonal changes and iron and folate status. Standard medications for treating RLS during pregnancy are not established. Most medications have been used according to the evidence from non-pregnant patients. Therefore, consideration of the medical treatment for treating RLS during pregnancy should be balanced between the benefit of relieving the symptoms and maternal and fetal risk. In general, the prognosis of RLS during pregnancy is good and symptoms are usually relieved after delivery.

Gabapentin enacarbil for the treatment of moderate to severe primary restless legs syndrome (Willis-Ekbom disease): 600 or 1,200 mg dose?

Gabapentin enacarbil is a prodrug of the anticonvulsant gabapentin. The efficacy and safety of gabapentin enacarbil for the treatment of moderate to severe primary restless legs syndrome (RLS) has been evaluated in several clinical trials in the United States and Japan. Although most clinical trials assessed gabapentin enacarbil at doses greater than 600 mg/day and demonstrated the overall safety and efficacy (defined as improvements in the coprimary endpoints of the international RLS rating scale [IRLS] total score and Clinical Global Impression-Improvement response), the US Food and Drug Administration approved the 600 mg once-daily dosage because doses higher than 600 mg/day were considered to provide no additional benefits and were associated with higher rates of adverse events, such as somnolence and dizziness. Nonetheless, the results of clinical trials and post hoc meta-analyses have indicated that the 1,200 mg once-daily dosage was the most validated gabapentin enacarbil treatment for not only subjective RLS symptoms but also severe sleep disturbance associated with RLS. A Japanese dose-finding study showed that 900 mg/day, the intermediate dose between 600 and 1,200 mg, failed to show a significant improvement in IRLS total score, probably because many of the patients who discontinued treatment did so early, suggesting that a half-landing dose may cause more adverse effects than favorable ones in some RLS patients early in the treatment. Gabapentin enacarbil may have two distinct therapeutic doses for the treatment of RLS: 600 mg/day or lower doses for the treatment of subjective RLS symptoms and 1,200 mg/day or higher doses for the treatment of both subjective RLS symptoms and associated problems such as severe sleep disturbances.

Treatment of restless legs syndrome

Restless legs syndrome (RLS) is a common disorder diagnosed by the clinical characteristics of restlessness in the legs associated often with abnormal sensations that start at rest and are improved by activity, occurring with a diurnal pattern of worsened symptoms at night and improvement in the morning. RLS is the cause of impaired quality of life in those more severely afflicted. Treatment of RLS has undergone considerable change over the last few years. Several classes of medications have demonstrated efficacy, including the dopaminergic agents and the alpha-2-delta ligands. Levodopa was the first dopaminergic agent found to be successful. However, chronic use of levodopa is frequently associated with augmentation that is defined as an earlier occurrence of symptoms frequently associated with worsening severity and sometimes spread to other body areas. The direct dopamine agonists, including ropinirole, pramipexole, and rotigotine patch, are also effective, although side effects, including daytime sleepiness, impulse control disorders, and augmentation, may limit usefulness. The alpha-2-delta ligands, including gabapentin, gabapentin enacarbil, and pregabalin, are effective for RLS without known occurrence of augmentation or impulse control disorders, although sedation and dizziness can occur. Other agents, including the opioids and clonazepam do not have sufficient evidence to recommend them as treatment for RLS, although in an individual patient, they may provide benefit.

Review: management of Parkinson's disease

Parkinson's disease (PD) is one of the most frequent neurological diseases. Despite the modern imaging and nuclear techniques which help to diagnose it in a very early stage and lead to a better discrimination of similar diseases, PD has remained a clinical diagnosis. The increasing number of available treatment options makes the disease management often complicated even when the presence of PD seems undoubted. In addition, nonmotor symptoms and side effects of some therapies constitute some pitfalls already in the preclinical state or at the beginnings of the disease, especially with the progressive effect on patients. Therefore, this review aimed to summarize study results and depict recommended medical treatments for the most common motor and nonmotor symptoms in PD. Additionally, emerging new therapeutic options such as continuous pump therapies, eg, with apomorphine or parenteral levodopa, or the implantation of electrodes for deep brain stimulation were also considered.

Gabapentin enacarbil in Japanese patients with restless legs syndrome: a 12-week, randomized, double-blind, placebo-controlled, parallel-group study

OBJECTIVE

Gabapentin enacarbil (GEn) was effective and well-tolerated for the treatment of restless legs syndrome (RLS) in North American studies. However, no placebo-controlled studies of GEn have been performed in Asian patients with RLS. Therefore, we investigated the efficacy and safety of GEn in Japanese patients with RLS to determine the optimal dosage.

RESEARCH DESIGN AND METHODS

Outpatients with RLS (International Restless Legs Syndrome Rating Scale (IRLS) scores ≥15) were randomized (n = 474) and treated (n = 469) in a double-blind manner with once-daily placebo (n = 116), 600 (n = 120), 900 (n = 119) or 1200 (n = 114) mg GEn for 12 weeks.

CLINICAL TRIAL REGISTRATION

NCT00530530 (ClinicalTrials.gov)

MAIN OUTCOME MEASURE

The primary outcome was the change in IRLS score. Secondary outcomes included Investigator (ICGI)- and Patient (PCGI)-rated Clinical Global Impression and adverse events.

RESULTS

The mean change in IRLS score from baseline to the final observation was -8.96 for placebo versus -11.10, -10.28 and -11.38 for 600, 900 and 1200 mg GEn. Williams' multiple comparison test showed that only 1200 mg GEn was superior to placebo (p = 0.011). However, in post hoc mixed-effects models with repeated measures, which accounted for the time-course of changes in IRLS, the placebo-adjusted changes were -2.31, -1.92 and -2.31 for 600, 900 and 1200 mg GEn. ICGI and PCGI response rates were significantly greater for all three GEn doses versus placebo (all p ≤ 0.014). Adverse events, including somnolence, dizziness and nasopharyngitis, were frequent but of mild-to-moderate severity. However, there was a tendency toward a dose-dependent increase in the incidence of adverse events.

CONCLUSIONS

GEn is effective and well-tolerated for the treatment of RLS in Japanese patients. All three doses produced improvements in IRLS compared with placebo; 600 mg GEn is a suitable target dose. However, our analysis possibly introduced positive bias by assuming that symptoms improve after discontinuation.

Gabapentin enacarbil: in patients with restless legs syndrome

Oral gabapentin enacarbil is approved in adult patients for the treatment of moderate to severe primary restless legs syndrome (RLS) [featured indication] and the management of postherpetic neuralgia. In the 12-week Patient Improvements in Vital Outcomes following Treatment (PIVOT) RLS I and II trials in adult patients with moderate to severe primary RLS (n > 500 total evaluable), once-daily gabapentin enacarbil 600 or 1,200 mg significantly improved mean International Restless Legs Scale (IRLS) total scores compared with placebo, with significantly higher investigator-rated Clinical Global Impression-Improvement (CGI-I) responder rates in gabapentin enacarbil groups than in placebo groups. Improvements in other sleep outcomes (assessed using various scales) also generally favoured gabapentin enacarbil treatment. These data are supported by results from a polysomnography, crossover (two 4-week treatment periods) trial (n > 100 evaluable). Improvements in RLS symptoms with gabapentin enacarbil were maintained in a 52-week extension study of clinical trials, including PIVOT RLS I and II. The longer-term efficacy of gabapentin enacarbil in patients with moderate to severe RLS was also demonstrated in the 36-week PIVOT RLS Maintenance study and a 52-week noncomparative study conducted in Japan. Gabapentin enacarbil was generally well tolerated in adult patients with RLS participating in short- and longer-term clinical trials. The most common treatment-emergent adverse events were somnolence/sedation and dizziness. Most adverse events were of mild to moderate severity, with relatively few patients discontinuing treatment because of an adverse event.

Strategies for the treatment of restless legs syndrome

Restless legs syndrome (RLS) is a common neurological disorder of unknown etiology that is managed by therapy directed at relieving its symptoms. Treatment of patients with milder symptoms that occur intermittently may be treated with nonpharmacological therapy but when not successful, drug therapy should be chosen based on the timing of the symptoms and the needs of the patient. Patients with moderate to severe RLS typically require daily medication to control their symptoms. Although the dopamine agonists, ropinirole and pramipexole have been the drugs of choice for patients with moderate to severe RLS, drug emergent problems like augmentation may limit their use for long term therapy. Keeping the dopamine agonist dose as low as possible, using longer acting dopamine agonists such as the rotigotine patch and maintaining a high serum ferritin level may help prevent the development of augmentation. The α2δ anticonvulsants may now also be considered as drugs of choice for moderate to severe RLS patients. Opioids should be considered for RLS patients, especially for those who have failed other therapies since they are very effective for severe cases. When monitored appropriately, they can be very safe and durable for long term therapy. They should also be strongly considered for treating patients with augmentation as they are very effective for relieving the worsening symptoms that occur when decreasing or eliminating dopamine agonists.

Pediatric sleep pharmacology

This article reviews common sleep disorders in children and pharmacologic options for them. Discussions of pediatric sleep pharmacology typically focus on treatment of insomnia. Although insomnia is a major concern in this population, other conditions of concern in children are presented, such as narcolepsy, parasomnias, restless legs syndrome, and sleep apnea.

Review of the treatment of restless legs syndrome: focus on gabapentin enacarbil

The FDA approved gabapentin enacarbil in 2011 as the first non-dopaminergic agent for the treatment of restless legs syndrome (RLS) symptoms. Although gabapentin enacarbil is a pro-drug of gabapentin, its pharmacokinetics differ. Absorption of gabapentin enacarbil is more predictable, and inter-patient variability in bioavailability is lower than that of gabapentin. Studies have demonstrated superiority of gabapentin enacarbil compared to placebo. Comparisons to currently available RLS treatments are lacking, but clinical trials demonstrate comparable improvement in RLS symptoms to the dopamine agonists ropinirole and pramipexole, which are usually considered first-line therapy for daily RLS symptoms. Gabapentin enacarbil was well tolerated in clinical trials. The role of the drug in RLS treatment remains undefined, although it will likely be used as an alternative for refractory RLS when other treatments have failed. Additionally, gabapentin enacarbil may be recommended for patients with daily RLS symptoms that are less intense or are associated with pain as an alternative to dopamine agonists.

Dose response of Gabapentin Enacarbil versus placebo in subjects with moderate-to-severe primary restless legs syndrome: an integrated analysis of three 12-week studies

BACKGROUND

The efficacy and tolerability of gabapentin enacarbil (Horizant®; GlaxoSmithKline, Brentford, UK) has been demonstrated in several restless legs syndrome (RLS) phase II and phase III clinical studies at various doses from 600 mg to 2400 mg.

OBJECTIVE

The objective of this study was to evaluate key efficacy and safety outcomes in subjects with RLS treated with once-daily gabapentin enacarbil 600 mg, 1200 mg, 1800 mg and 2400 mg, providing supportive evidence of the efficacy of gabapentin enacarbil 600 mg compared with higher doses and placebo.

STUDY DESIGN

Integrated post hoc analysis of three 12-week, randomized, double-blind, placebo-controlled trials in subjects with RLS.

SETTING

The three studies were carried out at multiple centres in the US.

PATIENTS

In total, 760 subjects were included in the pooled analysis (placebo, n = 245; gabapentin enacarbil 600 mg, n = 163; gabapentin enacarbil 1200 mg, n = 269; gabapentin enacarbil 1800 mg, n = 38; gabapentin enacarbil 2400 mg, n = 45).

INTERVENTION

In all studies, gabapentin enacarbil or placebo was administered once daily at approximately 5 p.m. with food. Gabapentin enacarbil was initiated at a dose of 600 mg with subsequent titration in 600 mg increments every 3 days up to the randomized dose.

MAIN OUTCOME MEASURE

The efficacy endpoints analysed for the purpose of this integrated analysis were change from baseline in International Restless Legs Scale (IRLS) total score and the proportion of responders (subjects rated as 'much' or 'very much' improved) on the investigator-rated Clinical Global Impression-Improvement (CGI-I) scale. Safety endpoints assessed were the incidence of treatment-emergent adverse events (AEs) and serious AEs.

RESULTS

Gabapentin enacarbil 600 mg significantly improved IRLS total score compared with placebo (adjusted mean [standard error] change in IRLS total score from baseline to week 12 last observation carried forward: -13.6 [0.71] vs -9.3 [0.55]; adjusted mean treatment difference: -4.3; 95% CI -6.01, -2.52; p < 0.0001). A significantly higher proportion of subjects was rated as responders on the investigator-rated CGI-I scale with gabapentin enacarbil 600 mg compared with placebo (70.2% vs 42.2%; adjusted odds ratio 3.1; 95% CI 1.96, 4.89; p < 0.0001). Similar treatment benefits were seen with both efficacy endpoints for the three higher doses. The AEs reported most frequently were somnolence and dizziness; there was a dose-response relationship to these AEs. No new or unexpected safety issues were identified by this integrated analysis.

CONCLUSION

The lowest dose of gabapentin enacarbil evaluated (600 mg) significantly improved RLS symptoms compared with placebo. The safety profile was consistent with that described previously in the literature.

The treatment of restless legs syndrome and periodic limb movement disorder in adults--an update for 2012: practice parameters with an evidence-based systematic review and meta-analyses: an American Academy of Sleep Medicine Clinical Practice Guideline

A systematic literature review and meta-analyses (where appropriate) were performed to update the previous AASM practice parameters on the treatments, both dopaminergic and other, of RLS and PLMD. A considerable amount of literature has been published since these previous reviews were performed, necessitating an update of the corresponding practice parameters. Therapies with a STANDARD level of recommendation include pramipexole and ropinirole. Therapies with a GUIDELINE level of recommendation include levodopa with dopa decarboxylase inhibitor, opioids, gabapentin enacarbil, and cabergoline (which has additional caveats for use). Therapies with an OPTION level of recommendation include carbamazepine, gabapentin, pregabalin, clonidine, and for patients with low ferritin levels, iron supplementation. The committee recommends a STANDARD AGAINST the use of pergolide because of the risks of heart valve damage. Therapies for RLS secondary to ESRD, neuropathy, and superficial venous insufficiency are discussed. Lastly, therapies for PLMD are reviewed. However, it should be mentioned that because PLMD therapy typically mimics RLS therapy, the primary focus of this review is therapy for idiopathic RLS.

Role of gabapentin enacarbil XR in restless legs syndrome

Gabapentin enacarbil XR is a new extended-release formulation which attempts to overcome the reduced efficacy of shorter-acting gabapentin, with sustained delivery over a 24-hour period. It is a gabapentin prodrug which is efficiently and rapidly converted to gabapentin during active transport throughout the length of the intestine via high-capacity monocarboxylate type 1 nutrient transporters unlike its predecessor, which is absorbed via low-capacity transporters largely confined to the upper intestinal region. Its lack of saturable absorption allows for dose-proportional absorption and hence increased bioavailability. Several clinical trials addressing its efficacy in moderate to severe restless legs syndrome (RLS) demonstrate improvements in the International RLS Rating Scale after a 2-week to 3-month period. Open-label studies of 52 weeks' duration showed maintenance of symptom reduction with once-daily administration of the extended-release formulation. The most commonly reported treatment-emergent adverse effects were somnolence and dizziness. Although the incidence of emergent adverse effects is high, it is comparable with that of gabapentin. No studies thus far have documented augmentation as an issue, unlike that observed with most dopaminergic agents. In addition, both dopamine precursors and agonists have not been shown to increase slow wave sleep or improve overall sleep architecture consistently despite improvement in the periodic leg movement index, in contrast with gabapentin enacarbil. Presently, gabapentin enacarbil has not been approved by the Therapeutic Goods Administration or Medsafe for use in RLS. The cost of this medication may also be a potential barrier for many patients. Future comparative efficacy studies with gabapentin, first-line dopaminergic agents, rotigotine, being the other once daily RLS medication, and pregabalin, the structural analog of gabapentin, will be necessary.

Restless legs syndrome: a comprehensive overview on its epidemiology, risk factors, and treatment

PURPOSES

Restless legs syndrome (RLS) is underdiagnosed and poorly understood by clinicians and the general public alike; accordingly, a broad literature review with information most relevant to general practice is needed to help dispel misconceptions and improve level of care.

METHODS

Specifically, this review comprehensively provides an epidemiological analysis of RLS and examines the risk factors and treatment options for RLS by compiling the findings of past RLS studies. These RLS studies were identified through a retrospective PubMed search. The epidemiological analysis was conducted by calculating a weighted mean average of all the relevant general population RLS prevalence studies, separated into geographical/racial categories.

RESULTS

A comprehensive analysis of RLS epidemiological studies finds the prevalence rate of RLS to be 5-15% in the general population with 2.5% of adults having symptoms severe enough to require medical intervention. Some of the risk factors for RLS include female gender, pregnancy, low iron levels, lower socioeconomic status, poor health, elderly age, comorbidity with Parkinson's disease, positive family history of RLS, and comorbidity with psychiatric disorders. A wide array of treatment options exist for RLS including pharmacological and nonpharmacologic interventions.

CONCLUSIONS

Clinicians' understanding of RLS enigma has recently improved due to the increased intensity of RLS research over the past decade. This review summarizes the current findings in the RLS field as well as providing guidelines for future RLS-related research.

The use of gabapentin enacarbil in the treatment of restless legs syndrome

Restless legs syndrome (RLS) is a common sleep-related neurological disorder that is characterized by the urge to move, worsening at rest, improvement with activity, and worsening in the evening and night. Dopamine agonists are usually the first-line therapy. Other agents including benzodiazepines, narcotics, and anticonvulsants have been used to treat RLS. Gabapentin has been shown to improve RLS in a small number of clinical studies, but is limited by its short half-life and variable bioavailability. Gabapentin enacarbil is a novel prodrug of gabapentin designed to overcome these pharmacokinetic limitations. In vitro and in vivo studies have demonstrated that gabapentin enacarbil has improved absorption, bioavailability and pharmacokinetics compared with gabapentin. Phase II and III studies have demonstrated that gabapentin enacarbil is generally well tolerated and is useful in the treatment of RLS.