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

Does Dexmedetomidine Improve or Worsen Restless Leg Syndrome under Sedation: A Case Report and Extensive Review

Background

Restless leg syndrome (RLS) is a common neurological condition that manifests as creeping, nonpainful urges to move lower extremities and is relieved with movements of the legs. RLS is associated with comorbidities such as gastric surgery, diabetes mellitus, uremia, and iron deficiency anemia, and it is misdiagnosed in many cases. Drugs like levodopa, ropinirole, pramipexole, cabergoline, and pergolide that target the dopaminergic system have been traditionally used to treat symptoms of RLS. α2-adrenoceptor (α2-AR) agonists, like clonidine and dexmedetomidine, have also been reported to show improvement of RLS symptoms during sedation. Specific Aim. This case report suggests that dexmedetomidine may have worsened RLS during sedation in a 71-year-old male with no prior diagnosis of RLS or reported symptoms. The patient had a procedure for right first metatarsophalangeal joint (MTPJ) fusion, with second digit proximal interphalangeal joint (PIPJ) arthrodesis, and flexor tendon transfer due to pain on walking and failing conservative therapy. He underwent intravenous sedation/monitored anesthesia care (MAC) with propofol, dexmedetomidine, and a peripheral regional block for intraoperative anesthesia and postoperative analgesia. During the surgery, the patient experienced continuous bilateral leg movement, unpredictable, and unrelated to surgical stimulation or level of consciousness within 5 minutes of administration of dexmedetomidine. The patient tolerated the procedure, and the unpredicted leg movement was managed by the surgeons intraoperatively.

Conclusion

Although no previous literature exists and mechanisms are unclear, this case report hypothesizes that dexmedetomidine may contribute to worsening RLS symptoms.

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.

[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.

Quantitative Comparison of the Efficacies of 5 First-Line Drugs for Primary Restless Leg Syndrome

Comparative analyses of the efficacies of dopaminergic agonists (pramipexole, ropinirole, and rotigotine patch) and α-2-δ ligands (gabapentin enacarbil and pregabalin) for treatment of primary restless leg syndrome (RLS) are lacking because of the few head-to-head clinical trials. A model-based meta-analysis approach was employed to quantitatively compare the efficacies of these 5 first-line RLS drugs. Longitudinal efficacy data of RLS drugs were collected from published eligible literature. Mean changes in both the International Restless Leg Syndrome Study Group (IRLS) rating scale and Clinical Global Impression Improvement (CGI-I) scale response rate were analyzed. A study-level population pharmacodynamic model was used to fit the dose-effect relationship and to describe the therapeutic effect over time for RLS drugs and placebo, and the typical efficacies of these drugs were compared. The onset of action was rapid for RLS drugs. In the placebo group, typical maximum IRLS reduction (E_max,IRLS ) and CGI-I response rate (E_max,CGI-I ) were -9.34 points and 48.2%, respectively. After deducting placebo effects, we found that the baseline IRLS score was significantly correlated with the E_max,IRLS of dopaminergic agonists. Typical E_max,IRLS of dopaminergic agonists was expressed as - 7.7 - 0.682 × ( baseline IRLS score - 24 ) points. Typical E_max,IRLS values of pregabalin and gabapentin enacarbil were -5.95 points and -4.00 points, respectively. The therapeutic effect of dopaminergic agonists was found to be associated with baseline symptom severity. In RLS patients with more severe symptoms, the therapeutic effect of dopaminergic agonists tended to be better than that of α-2-δ ligands.

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.

An update on the treatment of Restless Legs Syndrome/Willis-Ekbom Disease: prospects and challenges

INTRODUCTION

Restless Legs Syndrome/Willis-Ekbom Disease (RLS/WED) is a sleep disorder characterized by an urge to move the legs, frequently associated or triggered by unpleasant sensations in the lower limbs that affects approximately 2.5% of adults. Therapy and management of RLS/WED require long-term interventions, since the typical manifestation of this disorder is chronic. Areas covered: In this review, we provide an update regarding the treatment of RLS/WED with particular attention to future challenges for its management. We reviewed a large variety of treatments studied in clinical trials and supported by the most updated guidelines. Alongside with first-line interventions other pharmacological options including opioids, benzodiazepines, iron therapy, and newly studied drugs are discussed. Furthermore, due to the occurrence of augmentation and worsening of symptoms we also reviewed the development of non-pharmacologic alternatives. Expert commentary: The management of RLS/WED is a challenge because of different long-term issues. Several complications, such as loss of the therapeutic effect of dopaminergic or non-dopaminergic agents and augmentation, are still unsolved concerns. However, the development of new drugs acting on adenosinergic and glutamatergic neurotransmission seems promising. Randomized controlled trials are needed in order to recognize effectiveness of new drugs or non-pharmacological treatment strategies.

French consensus: Treatment of newly diagnosed restless legs syndrome

Treatment of restless legs syndrome (RLS) must only be considered after a definite positive diagnosis. The RLS phenotype must be characterised precisely, iron deficiency always tested for, and aggravating factors eliminated when possible. Medical treatment is considered for severe or very severe forms and based on dopaminergic agonists, α2δ-1 ligands and/or opioids. First line treatment will be a low-dose monotherapy and the choice of treatment depends on the results of the clinical examination and investigations.

Gabapentin enacarbil, pregabalin and rotigotine are equally effective in restless legs syndrome: a comparative meta-analysis

To synthesize evidence from available randomized controlled trials (RCT) to compare the efficacies of dopaminergic drugs (pramipexole, ropinirole and rotigotine) and α-2-δ ligands (gabapentin enacarbil and pregabalin) for the treatment of restless legs syndrome (RLS). We searched PubMed for all eligible RCTs. Network meta-analysis using frequentist methodology with random effect models was performed for mean changes in scores on the International RLS Study Group Rating Scale (IRLS) and for responder rates on Clinical Global Impressions-Improvement (CGI-I); analyzed as odds ratio (OR). Network meta-analysis of mean changes in IRLS data from 35 studies with 7333 participants showed that all treatments, in specific gabapentin enacarbil, followed by pregabalin and rotigotine were superior to placebo [mean reduction in IRLS scores: -5.31 (-6.74 to -3.87), -5.20 (-6.91 to -3.49), 5.17 (3.73-6.61), respectively] but there were no significant differences between active treatments. Network meta-analysis of 5137 participants from 24 studies showed that gabapentin enacarbil and rotigotine were associated with the highest CGI-I response rates [ORs: 5.68; (95% CI, 4.14-7.21); and 4.68 (2.87-6.49), compared to placebo, respectively]. No significant inter-treatment differences exist, except for that between gabapentin enacarbil and ropinirole. Based on IRLS scores and CGI-I response rates, while gabapentin enacarbil, pregabalin and rotigotine stand out as the most efficacious of all examined drugs, it is noteworthy that no significant inter-treatment differences exist, except for that between gabapentin enacarbil and ropiniriole (for CGI-I response rates).

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.

Achievements, challenges, and future perspectives of epidemiologic research in restless legs syndrome (RLS)

In the 20 years since the initial consensus on a common definition for restless legs syndrome (RLS), over 600 scientific reports on epidemiological aspects of RLS have been published. Most are descriptive and address important issues such as prevalence, familial patterns, comorbidities, and quality of life. While the establishment of prospective cohort studies and the use of secondary data sources are rather new to RLS research, both options significantly broaden the possibilities for analysis of disease risk factors. These two options, as well as the inclusion of a broader phenotyping of individual patients, have great potential to elucidate etiologic factors for RLS and expand knowledge about this common disorder. This article summarizes achievements in the area of RLS epidemiology, describes current challenges, and highlights future perspectives in the field.

The Effect of Gabapentin Enacarbil on Pain Associated with Moderate-to-Severe Primary Restless Legs Syndrome in Adults: Pooled Analyses from Three Randomized Controlled Trials

BACKGROUND

Adults with moderate-to-severe primary restless legs syndrome (RLS) often experience painful dysesthesias, which may lead to impaired quality of life.

OBJECTIVES

The aim of this study was to assess the effects of gabapentin enacarbil (GEn) on pain associated with moderate-to-severe primary RLS in adults.

METHODS

Data were pooled from three double-blind, randomized, placebo-controlled, 12-week trials (NCT00298623, NCT00365352, NCT01332305) for adults receiving GEn or placebo once daily. Change in average daily RLS pain score and a combined International Restless Legs Scale (IRLS)-pain response were examined.

RESULTS

The modified intention-to-treat population included 671 adults (placebo, n = 244; GEn 600 mg, n = 161; GEn 1200 mg, n = 266). Both GEn doses significantly improved average daily RLS pain score at week 12 (p < 0.001 for GEn 600 mg vs. placebo and GEn 1200 mg vs. placebo). The combined IRLS-pain response subanalysis included 366 patients with a baseline IRLS total score ≥15 and pain score ≥4 (placebo, n = 133; GEn 600 mg, n = 86; GEn 1200 mg, n = 147). Most patients were both IRLS and pain responders (placebo, 40 %; GEn 600 mg, 70 %; GEn 1200 mg, 67 %). Spearman rank correlations between IRLS total and pain score (change from baseline to week 12) were moderate or strong. The most frequent treatment-emergent adverse events were somnolence (placebo, 5 %; GEn 600 mg, 20 %; GEn 1200 mg, 23 %) and dizziness (placebo, 4 %; GEn 600 mg, 13 %; GEn 1200 mg, 22 %).

CONCLUSIONS

This post hoc pooled analysis suggests that GEn (600 and 1200 mg) once daily significantly improved pain associated with moderate-to-severe primary RLS in adults; however, the analysis was not powered to detect statistical differences between the two GEn doses. Numerically, more GEn-treated patients had a combined IRLS-pain response than placebo-treated patients.

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

OBJECTIVE

The aim was to assess gabapentin enacarbil (GEn) treatment effects on quality of life (QOL) and mood in adults with moderate-to-severe primary restless legs syndrome (RLS).

METHODS

Data were pooled from three placebo-controlled, randomized, double-blind, 12-week trials for adults receiving GEn (600 mg or 1200 mg) or placebo once daily. QOL was assessed with the RLS QOL questionnaire in two studies. Mood was examined with the Profile of Mood States Brief Form (POMS-B), and as an exploratory analysis with International Restless Legs Scale (IRLS) item 9 (daily affairs) and item 10 (mood disturbance) across all three studies. Mood and QOL were secondary endpoints in the individual clinical trials. No adjustments for multiplicity were applied.

RESULTS

The QOL analysis modified intent-to-treat (MITT) population included 541 adults (placebo, n = 204; GEn 600 mg, n = 114; GEn 1200 mg, n = 223). Both GEn doses significantly improved QOL versus placebo (week 12; p < 0.01). The mood analysis MITT population included 671 adults (placebo, n = 244; GEn 600 mg, n = 161; GEn 1200 mg, n = 266). GEn 600 mg significantly improved POMS vigor-activity versus placebo (week 12; p < 0.05); other POMS criteria were not significantly affected. GEn 1200 mg significantly improved POMS scores for total mood disturbance, depression-dejection, fatigue-inertia, vigor-activity, and confusion-bewilderment versus placebo at week 12 (p < 0.05); tension-anxiety and anger-hostility were not significantly affected. Both GEn doses significantly improved IRLS item 9 and item 10 versus placebo at week 12 (p < 0.05). The most frequent treatment-emergent adverse events with GEn were somnolence and dizziness.

CONCLUSIONS

GEn (600 mg and 1200 mg) once daily significantly improved QOL in adults with moderate-to-severe primary RLS at all time points examined. While the only POMS item significantly improved by GEn 600 mg versus placebo at week 12 was vigor-activity, GEn 1200 mg significantly improved total mood disturbance and several other POMS items versus placebo at week 12. Both QOL and mood improvements were numerically greater with GEn 1200 mg versus 600 mg.

TRIAL REGISTRATIONS

Clinicaltrials.gov identifiers NCT00298623, NCT00365352, NCT01332305.

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.

Therapeutic advances in restless legs syndrome (RLS)

Levodopa and dopamine agonists have been the main treatment for restless legs syndrome during the past decades. Although their efficacy has been well documented over the short term, long-term dopaminergic treatment is often complicated by augmentation, loss of efficacy, and other side effects. Recent large randomized controlled trials provide new evidence for the efficacy of high-potency opioids and α2δ ligands, and several post hoc analyses, meta-analyses, algorithms, and guidelines have been published, often with a specific focus, for example, on augmentation, or on management of restless legs syndrome during pregnancy. Several new contributions to understanding the pathophysiology of restless legs syndrome have been published, but at this time, whether they will have an impact on treatment possibilities in the future cannot be estimated.

Restless legs syndrome-current therapies and management of augmentation

Idiopathic restless legs syndrome (RLS) can severely affect quality of life and disturb sleep, so that pharmacological treatment is necessary, especially for elderly patients. Treatment guidelines recommend initiation of therapy with dopamine agonists (pramipexole, ropinirole or the rotigotine transdermal patch, all approved in most countries) or α-2-δ ligands (gabapentin enacarbil, approved in the USA and Japan), depending on the country and availability. Where approved, opioids (prolonged release oxycodone-naloxone, approved in Europe) are also recommended as a second-line therapy for severe RLS. Several iron formulations can be effective but are not yet approved for RLS therapy, whereas benzodiazepines and other anticonvulsants are not recommended or approved. Less is known about effective management of RLS that is associated with other conditions, such as uraemia or pregnancy. Furthermore, very little data are available on the management of RLS when first-line treatment fails or patients experience augmentation. In this Review, we summarize state-of-the-art therapies for RLS in the context of the diagnostic criteria and available guidelines, based on knowledge ranging from Class I evidence for the treatment of idiopathic RLS to Class IV evidence for the treatment of complications such as augmentation. We consider therapies, including combination therapies, that are used in clinical practice for long-term management of RLS, despite a lack of trials and approval, and highlight the need for practical long-term evaluation of current trials.

Augmentation of restless leg syndrome (Willis-Ekbom disease) during long-term dopaminergic treatment

Restless legs syndrome (RLS), also known as Willis-Ekbom disease (WED), is a common sensorimotor disorder that can generally be effectively managed in the primary care clinic. However, some treatment complications may arise. According to the recommendations of the International Restless Legs Syndrome Study Group, non-ergot dopamine-receptor agonists have over the past years been one of the first-line treatments for patients with RLS/WED requiring pharmacological therapy. Augmentation is the main complication of long-term dopaminergic treatment of RLS/WED and is defined as an overall worsening of symptoms beyond pretreatment levels in patients who experienced an initial positive therapeutic response. Once identified on the basis of its characteristic clinical features, augmentation requires careful management. In order to provide clinicians with a comprehensive understanding of this common treatment complication, this review discusses the clinical features of augmentation, and its differentiation from morning rebound, symptom fluctuations and natural disease progression. Reported incidences of augmentation in clinical trials of dopaminergic RLS/WED therapies are summarized. Finally, the hypothetical pathophysiology of augmentation and the current recommendations for management of patients with augmented RLS/WED symptoms are discussed.

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.

Demographic and clinical characteristics of patients with restless legs syndrome in spine clinic

Objective

The restless legs syndrome (RLS) is a common disorder affecting up to 5% to 15% of the general population, in which the incidence increases with age, and includes paresthesia in the legs. The purpose of this study is to investigate the incidence of RLS in spine center and to review clinical manifestations of this syndrome and its current treatments.

Methods

Over a period of a year, retrospective medical record review and lumbar magnetic resonance images were performed on 32 patients with RLS in spine clinic who were diagnosed by National Institutes of Health criteria. Affected limbs were classified as five. Two grading systems were used in the evaluation of neural compromises.

Results

The incidence of RLS was 5.00% (32/639). There were 16 males (50%) and 16 females (50%). The median age at diagnosis was 55.4 years (range, 25-93 years). There are no correlation between the affected limbs of RLS and neural compromises on the lumbar spine.

Conclusion

The RLS is a clearly common neurologic disorder of the limbs, usually the legs. The awareness of this syndrome can help reduce diagnostic error; thereby, avoiding the morbidity and expense associated with unnecessary studies or inappropriate treatments in RLS patients.

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.