The use of gabapentin enacarbil in the treatment of 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.

Proteostasis failure exacerbates neuronal circuit dysfunction and sleep impairments in Alzheimer's disease

Failed proteostasis is a well-documented feature of Alzheimer's disease, particularly, reduced protein degradation and clearance. However, the contribution of failed proteostasis to neuronal circuit dysfunction is an emerging concept in neurodegenerative research and will prove critical in understanding cognitive decline. Our objective is to convey Alzheimer's disease progression with the growing evidence for a bidirectional relationship of sleep disruption and proteostasis failure. Proteostasis dysfunction and tauopathy in Alzheimer's disease disrupts neurons that regulate the sleep-wake cycle, which presents behavior as impaired slow wave and rapid eye movement sleep patterns. Subsequent sleep loss further impairs protein clearance. Sleep loss is a defined feature seen early in many neurodegenerative disorders and contributes to memory impairments in Alzheimer's disease. Canonical pathological hallmarks, β-amyloid, and tau, directly disrupt sleep, and neurodegeneration of locus coeruleus, hippocampal and hypothalamic neurons from tau proteinopathy causes disruption of the neuronal circuitry of sleep. Acting in a positive-feedback-loop, sleep loss and circadian rhythm disruption then increase spread of β-amyloid and tau, through impairments of proteasome, autophagy, unfolded protein response and glymphatic clearance. This phenomenon extends beyond β-amyloid and tau, with interactions of sleep impairment with the homeostasis of TDP-43, α-synuclein, FUS, and huntingtin proteins, implicating sleep loss as an important consideration in an array of neurodegenerative diseases and in cases of mixed neuropathology. Critically, the dynamics of this interaction in the neurodegenerative environment are not fully elucidated and are deserving of further discussion and research. Finally, we propose sleep-enhancing therapeutics as potential interventions for promoting healthy proteostasis, including β-amyloid and tau clearance, mechanistically linking these processes. With further clinical and preclinical research, we propose this dynamic interaction as a diagnostic and therapeutic framework, informing precise single- and combinatorial-treatments for Alzheimer's disease and other brain disorders.

Carbamate group as structural motif in drugs: a review of carbamate derivatives used as therapeutic agents

Due to their very good chemical and proteolytic stability, ability to penetrate cell membranes, and resemblance to a peptide bond, carbamate derivatives have received much attention in recent years and got an important role in modern drug discovery and medicinal chemistry. Today, carbamates make structural and/or functional part of many drugs and prodrugs approved and marketed for the treatment of various diseases such as cancer, epilepsy, hepatitis C, HIV infection, and Alzheimer's disease. In drugs they can play a role in drug-target interaction or improve the biological activity of parent molecules. In prodrugs they are mainly used to delay first-pass metabolism and enhance the bioavailability and effectiveness of compounds. This brief review takes a look at the properties and use of carbamates in various fields of medicine and provides quick insights into the mechanisms of action for some of them.

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.].

Evaluation of Acupuncture in the Treatment of Restless Legs Syndrome: A Randomized Controlled Trial

The aim of this study was to examine the additive effect of medical acupuncture on controlling the symptoms of restless legs syndrome (RLS). A total of 46 randomly allocated patients diagnosed with RLS were assigned to receive either 10 sessions of acupuncture plus gabapentin (300 mg/d), or gabapentin (300 mg/d) alone (23 patients in each group) over 4 weeks in a single-blind study. The symptoms of patients were assessed by the Visual Analogue Scale (VAS), the International Restless Legs Syndrome Rating Scale (IRLSRS), and the Pittsburgh Sleep Quality Index (PSQI) at baseline, just after the therapeutic course and 8 weeks later. For all outcome measures, there was a significant time-group interaction, showing that the behavior of groups differed regarding changes in VAS, IRLSRS, and PSQI in favor of the experimental group. After therapeutic course termination and in 8 weeks follow up, VAS and IRLSRS had a significant improvement in both the experimental group and the control group, but PSQI improved significantly just in the experimental group. Based on the findings of the present study, acupuncture plus a low dose of gabapentin (300 mg/d) is clinically useful in the treatment of RLS during 8 weeks follow up, and also has an additive therapeutic effect over gabapentin alone in patients with RLS.

Sleep dysfunction and its management in Parkinson's disease

OPINION STATEMENT

Sleep disorders are among the most common non-motor symptoms in Parkinson's Disease (PD). In some cases, symptoms can precede a diagnosis of PD by many years, but otherwise they are commonly encountered during the clinical care of patients. Unfortunately, sleep problems are under-recognized and subsequently inadequately addressed. In our experience, when properly addressed, physicians and patients are quickly aware of the often-debilitating nature of sleep dysfunction. This does not mean that solutions are easily attainable. Sleep in PD is held in a delicate balance, influenced by the disease process, medications, co-morbid symptoms, and a variety of other factors. For this reason, management of sleep in PD often requires an inter-disciplinary approach. Physicians should have an intimate knowledge of the many sleep problems apparent in PD, as well as appreciate the challenge presented by diverse therapeutic options that can both ameliorate and aggravate symptoms.

Prodrugs: a challenge for the drug development

It is estimated that about 10% of the drugs approved worldwide can be classified as prodrugs. Prodrugs, which have no or poor biological activity, are chemically modified versions of a pharmacologically active agent, which must undergo transformation in vivo to release the active drug. They are designed in order to improve the physicochemical, biopharmaceutical and/or pharmacokinetic properties of pharmacologically potent compounds. This article describes the basic functional groups that are amenable to prodrug design, and highlights the major applications of the prodrug strategy, including the ability to improve oral absorption and aqueous solubility, increase lipophilicity, enhance active transport, as well as achieve site-selective delivery. Special emphasis is given to the role of the prodrug concept in the design of new anticancer therapies, including antibody-directed enzyme prodrug therapy (ADEPT) and gene-directed enzyme prodrug therapy (GDEPT).

Parkinson's disease and sleep/wake disturbances

Parkinson's disease (PD) has traditionally been characterized by its cardinal motor symptoms of bradykinesia, rigidity, resting tremor, and postural instability. However, PD is increasingly being recognized as a multidimensional disease associated with myriad nonmotor symptoms including autonomic dysfunction, mood disorders, cognitive impairment, pain, gastrointestinal disturbance, impaired olfaction, psychosis, and sleep disorders. Sleep disturbances, which include sleep fragmentation, daytime somnolence, sleep-disordered breathing, restless legs syndrome (RLS), nightmares, and rapid eye movement (REM) sleep behavior disorder (RBD), are estimated to occur in 60% to 98% of patients with PD. For years nonmotor symptoms received little attention from clinicians and researchers, but now these symptoms are known to be significant predictors of morbidity in determining quality of life, costs of disease, and rates of institutionalization. A discussion of the clinical aspects, pathophysiology, evaluation techniques, and treatment options for the sleep disorders that are encountered with PD is presented.

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.

ADMET considerations for restless leg syndrome drug treatments

INTRODUCTION

Restless legs syndrome (RLS) is a common neurological disorder that might impair nocturnal rest causing decreased alertness, depressed mood, reduced job performance, and poor quality of life. In patients affected by severe RLS, a pharmacological treatment is mandatory.

AREAS COVERED

The present review is based on a search using PubMed from 1994 to 2012. It is focused on the Absorption, Distribution, Metabolism, Elimination and Toxicology (ADMET) characteristics of the most used medications for RLS. In particular, the ADMET characteristics of dopaminergic agents, anticonvulsants able to improve neuropathic pain, and iron were discussed.

EXPERT OPINION

Clinical trials have showed that non-ergolic dopamine agonists are efficacious and safe for patients affected by moderate to severe idiopathic RLS. However, no head-to-head study has compared the long-term effects of the three dopamine agonists approved by the FDA for RLS (ropinirole, pramipexole, and rotigotine). Moreover, further studies should investigate the extended-release formulation of ropinirole and pramipexole in RLS patients affected by all day long distressing symptoms. A standardized treatment for symptomatic forms of RLS is lacking. Randomized, placebo-controlled trials should be performed at least in RLS patients with peripheral neuropathic and chronic kidney disease. Concerning RLS due to iron deficiency, a head-to-head study comparing efficacy, safety and compliance of oral iron versus intravenous one seems to be needed.

Motor restlessness, sleep disturbances, thermal sensory alterations and elevated serum iron levels in Btbd9 mutant mice

Restless legs syndrome (RLS), also known as Willis-Ekbom disease, is a sensory-motor neurological disorder with a circadian component. RLS is characterized by uncomfortable sensations in the extremities, generally at night or during sleep, which often leads to an uncontrollable urge to move them for relief. Recently, genomic studies identified single-nucleotide polymorphisms in BTBD9, along with three other genes, as being associated with a higher risk of RLS. Little is known about the function of BTBD9 or its potential role in the pathophysiology of RLS. We therefore examined a line of Btbd9 mutant mice we recently generated for phenotypes similar to symptoms found in RLS patients. We observed that the Btbd9 mutant mice had motor restlessness, sensory alterations likely limited to the rest phase, and decreased sleep and increased wake times during the rest phase. Additionally, the Btbd9 mutant mice had altered serum iron levels and monoamine neurotransmitter systems. Furthermore, the sensory alterations in the Btbd9 mutant mice were relieved using ropinirole, a dopaminergic agonist widely used for RLS treatment. These results, taken together, suggest that the Btbd9 mutant mice model several characteristics similar to RLS and would therefore be the first genotypic mouse model of RLS. Furthermore, our data provide further evidence that BTBD9 is involved in RLS, and future studies of the Btbd9 mutant mice will help shine light on its role in the pathophysiology of RLS. Finally, our data argue for the utility of Btbd9 mutant mice to discover and screen novel therapeutics for RLS.

Prodrug approaches to reduce hyperexcitation in the CNS

Hyperexcitation in the central nervous system is the root cause of a number of disorders of the brain ranging from acute injury to chronic and progressive diseases. The major limitation to treatment of these ailments is the miniscule, yet formidable blood-brain barrier. To deliver therapeutic agents to the site of desired action, a number of biomedical engineering strategies have been developed including prodrug formulations that allow for either passive diffusion or active transport across this barrier. In the case of prodrugs, once in the brain compartment, the active therapeutic agent is released. In this review, we discuss in some detail a number of factors related to treatment of central nervous system hyperexcitation including molecular targets, disorders, prodrug strategies, and focused case studies of a number of therapeutics that are at a variety of stages of clinical development.