ADMET considerations when prescribing novel therapeutics to treat 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.

An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease

Sleep disorders are among the most common nonmotor symptoms in Parkinson's disease and are associated with reduced cognition and health-related quality of life. Disturbed sleep can often present in the prodromal or early stages of this neurodegenerative disease, rendering it crucial to manage and treat these symptoms. Levodopa and dopaminergic agonists are frequently prescribed to treat motor symptoms in Parkinson's disease, and there is increasing interest in how these pharmacological agents affect sleep and their effect on concomitant sleep disturbances and disorders. In this review, we discuss the role of dopamine in regulating the sleep-wake state and the impact of neurodegeneration on sleep. We provide an overview of the effects of levodopa and dopaminergic agonists on sleep architecture, insomnia, excessive daytime sleepiness, sleep-disordered breathing, rapid eye movement sleep behavior disorder, and restless legs syndrome in Parkinson's disease. Levodopa and dopaminergic drugs may have different effects, beneficial or adverse, depending on dosing, method of administration, and differential effects on the different dopamine receptors. Future research in this area should focus on elucidating the specific mechanisms by which these drugs affect sleep in order to better understand the pathophysiology of sleep disorders in Parkinson's disease and aid in developing suitable therapies and treatment regimens.

CITATION

Scanga A, Lafontaine A-L, Kaminska M. An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease. J Clin Sleep Med. 2023;19(6):1133-1144.

The Efficacy and Safety of Pharmacological Treatments for Restless Legs Syndrome: Systemic Review and Network Meta-Analysis

Although various drugs are currently used for restless legs syndrome (RLS) in clinic, selecting appropriate drugs for patients is difficult. This network meta-analysis (NMA) aimed to compare the efficacy and safety of different drugs. After literature searching and screening, 46 trials, including 10,674 participants are included in this NMA. The pooled results showed that, compared with placebo, only levodopa is inefficient to relieve symptoms of RLS. Cabergoline decreases IRLS scores to the greatest extent among all drugs (MD −11.98, 95% CI −16.19 to −7.78). Additionally, pramipexole is superior to ropinirole in alleviating symptoms of RLS (MD −2.52, 95% CI −4.69 to −0.35). Moreover, iron supplement alleviates RLS symptoms significantly compared with placebo in patient with iron deficiency (MD −5.15, 95% CI −8.99 to −1.31), but not for RLS patients with normal serum ferritin level (MD −2.22, 95% CI −6.99 to 2.56). For primary RLS, these drugs are also effective, while there is insufficient data to analyze drug efficacy in secondary RLS. We analyzed risk of common adverse effects of drugs including nausea, somnolence, fatigue, headache and nasopharyngitis. Alpha-2-delta ligands and DAs are favorable choices for both primary and secondary RLS because of their significant efficacy and good tolerability. Iron supplement can significantly alleviate symptoms of RLS patients with iron deficiency than placebo. We recommend gabapentin, gabapentin enacarbil, and pregabalin for clinicians for first consideration mainly because that they rarely cause augmentation. Oxycodone-naloxone could be considered in patients with severe or very severe RLS who failed in treatment with above drugs.

Employing in vitro metabolism to guide design of F-labelled PET probes of novel α-synuclein binding bifunctional compounds

A challenge in the development of novel ¹⁸F-labelled positron emission tomography (PET) imaging probes is identification of metabolically stable sites to incorporate the ¹⁸F radioisotope. Metabolic loss of ¹⁸F from PET probes in vivo can lead to misleading biodistribution data as displaced ¹⁸F can accumulate in various tissues.In this study we report on in vitro hepatic microsomal metabolism of novel caffeine containing bifunctional compounds (C₈-6-I, C₈-6-N, C₈-6-C₈) that can prevent in vitro aggregation of α-synuclein, which is associated with the pathophysiology of Parkinson's disease. The metabolic profile obtained guided us to synthesize stable isotope ¹⁹F-labelled analogues in which the fluorine was introduced at the metabolically stable N7 of the caffeine moiety.An in vitro hepatic microsomal metabolism study of the ¹⁹F-labelled analogues resulted in similar metabolites to the unlabelled compounds and demonstrated that the fluorine was metabolically stable, suggesting that these analogues are appropriate PET imaging probes. This straightforward in vitro strategy is valuable for avoiding costly stability failures when designing radiolabelled compounds for PET imaging.

Targinact for restless legs syndrome

Idiopathic restless legs syndrome (RLS)--also known as Willis-Ekbom disease--is a neurological condition characterised by an overwhelming urge to move the legs, occurring during rest or inactivity, especially at night. Symptoms are highly variable in frequency and severity, and can affect sleep and quality of life. First-line management includes addressing precipitating or aggravating factors and providing explanation, reassurance and advice on self-help strategies. Drug therapy (e.g. a dopamine agonist) is used for patients with more severe symptoms. In December 2014, the marketing authorisation for a modified-release preparation containing oxycodone and naloxone (Targinact-Napp Pharmaceuticals) was expanded to include use in the treatment of severe to very severe RLS after failure of dopaminergic therapy.(10)Here we review the management of adults with RLS, including the place of oxycodone/naloxone.

Phytochelators Intended for Clinical Use in Iron Overload, Other Diseases of Iron Imbalance and Free Radical Pathology

Iron chelating drugs are primarily and widely used in the treatment of transfusional iron overload in thalassaemia and similar conditions. Recent in vivo and clinical studies have also shown that chelators, and in particular deferiprone, can be used effectively in many conditions involving free radical damage and pathology including neurodegenerative, renal, hepatic, cardiac conditions and cancer. Many classes of phytochelators (Greek: phyto (φυτό)—plant, chele (χηλή)—claw of the crab) with differing chelating properties, including plant polyphenols resembling chelating drugs, can be developed for clinical use. The phytochelators mimosine and tropolone have been identified to be orally active and effective in animal models for the treatment of iron overload and maltol for the treatment of iron deficiency anaemia. Many critical parameters are required for the development of phytochelators for clinical use including the characterization of the therapeutic targets, ADMET, identification of the therapeutic index and risk/benefit assessment by comparison to existing therapies. Phytochelators can be developed and used as main, alternative or adjuvant therapies including combination therapies with synthetic chelators for synergistic and or complimentary therapeutic effects. The development of phytochelators is a challenging area for the introduction of new pharmaceuticals which can be used in many diseases and also in ageing. The commercial and other considerations for such development have great advantages in comparison to synthetic drugs and could also benefit millions of patients in developing countries.