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Frisaldi E, Vollert J, Al Sultani H, Benedetti F, Shaibani A. Placebo and nocebo responses in painful diabetic neuropathy: systematic review and meta-analysis. Pain 2024; 165:29-43. [PMID: 37530658 DOI: 10.1097/j.pain.0000000000003000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Accepted: 06/08/2023] [Indexed: 08/03/2023]
Abstract
ABSTRACT This preregistered (CRD42021223379) systematic review and meta-analysis aimed to characterize the placebo and nocebo responses in placebo-controlled randomized clinical trials (RCTs) on painful diabetic neuropathy (PDN), updating the previous literature by a decade. Four databases were searched for PDN trials published in the past 20 years, testing oral medications, adopting a parallel-group design. Magnitude of placebo or nocebo responses, Cochrane risk of bias, heterogeneity, and moderators were evaluated. Searches identified 21 studies (2425 placebo-treated patients). The overall mean pooled placebo response was -1.54 change in the pain intensity from baseline [95% confidence interval (CI): -1.52, -1.56, I 2 = 72], with a moderate effect size (Cohen d = 0.72). The pooled placebo 50% response rate was 25% [95% CI: 22, 29, I 2 = 50%]. The overall percentage of patients with adverse events (AEs) in the placebo arms was 53.3% [95% CI: 50.9, 55.7], with 5.1% [95% CI: 4.2, 6] of patients dropping out due to AEs. The year of study initiation was the only significant moderator of placebo response (regression coefficient = -0.06, [95% CI: -0.10, -0.02, P = 0.007]). More recent RCTs tended to be longer, bigger, and to include older patients (N = 21, rs = 0.455, P = 0.038, rs = 0.600, P = 0.004, rs = 0.472, P = 0.031, respectively). Our findings confirm the magnitude of placebo and nocebo responses, identify the year of study initiation as the only significant moderator of placebo response, draw attention to contextual factors such as confidence in PDN treatments, patients' previous negative experiences, intervention duration, and information provided to patients before enrollment.
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Affiliation(s)
- Elisa Frisaldi
- Rita Levi Montalcini Department of Neuroscience, University of Turin Medical School, Turin, Italy
| | - Jan Vollert
- Pain Research, Department of Surgery and Cancer, Imperial College London, London, United Kingdom
- Division of Neurological Pain Research and Therapy, Department of Neurology, University Hospital of Schleswig-Holstein, Campus Kiel, Kiel, Germany
- Department of Anaesthesiology, Intensive Care and Pain Medicine, University Hospital Muenster, Muenster, Germany
- Neurophysiology, Mannheim Center of Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany
| | | | - Fabrizio Benedetti
- Rita Levi Montalcini Department of Neuroscience, University of Turin Medical School, Turin, Italy
- Medicine and Physiology of Hypoxia, Plateau Rosà, Switzerland
| | - Aziz Shaibani
- Nerve and Muscle Center of Texas, Houston, TX, United States
- Baylor College of Medicine, Houston, TX, United States
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Scholz O, Huß E, Otter S, Herebian D, Hamacher A, Levy LM, Hristeva S, Sanz M, Ajani H, Puentes AR, Hoffmann T, Hogeback J, Unger A, Terheyden S, Reina do Fundo M, Dewidar B, Roden M, Lammert E. Protection of pancreatic islets from oxidative cell death by a peripherally-active morphinan with increased drug safety. Mol Metab 2023:101775. [PMID: 37451343 PMCID: PMC10403733 DOI: 10.1016/j.molmet.2023.101775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 06/06/2023] [Accepted: 07/07/2023] [Indexed: 07/18/2023] Open
Abstract
OBJECTIVE Dextromethorphan (DXM) is a commonly used antitussive medication with positive effects in people with type 2 diabetes mellitus, since it increases glucose tolerance and protects pancreatic islets from cell death. However, its use as an antidiabetic medication is limited due to its central nervous side effects and potential use as a recreational drug. Therefore, we recently modified DXM chemically to reduce its blood-brain barrier (BBB) penetration and central side effects. However, our best compound interacted with the cardiac potassium channel hERG (human ether-à-go-go-related gene product) and the μ-opioid receptor (MOR). Thus, the goal of this study was to reduce the interaction of our compound with these targets, while maintaining its beneficial properties. METHODS Receptor and channel binding assays were conducted to evaluate the drug safety of our DXM derivative. Pancreatic islets were used to investigate the effect of the compound on insulin secretion and islet cell survival. Via liquor collection from the brain and a behavioral assay, we analyzed the BBB permeability. By performing intraperitoneal and oral glucose tolerance tests as well as pharmacokinetic analyses, the antidiabetic potential and elimination half-life were investigated, respectively. To analyze the islet cell-protective effect, we used fluorescence microscopy as well as flow cytometric analyses. RESULTS Here, we report the design and synthesis of an optimized, orally available BBB-impermeable DXM derivative with lesser binding to hERG and MOR than previous ones. We also show that the new compound substantially enhances glucose-stimulated insulin secretion (GSIS) from mouse and human islets and glucose tolerance in mice as well as protects pancreatic islets from cell death induced by reactive oxygen species and that it amplifies the effects of tirzepatide on GSIS and islet cell viability. CONCLUSIONS We succeeded to design and synthesize a novel morphinan derivative that is BBB-impermeable, glucose-lowering and islet cell-protective and has good drug safety despite its morphinan and imidazole structures.
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Affiliation(s)
- Okka Scholz
- Institute of Metabolic Physiology, Heinrich Heine University, D-40225 Düsseldorf, Germany; Institute for Vascular and Islet Cell Biology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany; German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany
| | - Elena Huß
- Institute of Metabolic Physiology, Heinrich Heine University, D-40225 Düsseldorf, Germany; Institute for Vascular and Islet Cell Biology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany; German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany
| | - Silke Otter
- Institute of Metabolic Physiology, Heinrich Heine University, D-40225 Düsseldorf, Germany; Institute for Vascular and Islet Cell Biology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany; German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany
| | - Diran Herebian
- Department of General Pediatrics, Neonatology and Pediatric Cardiology, Medical Faculty and University Hospital, Heinrich Heine University, D-40225 Düsseldorf, Germany
| | - Anna Hamacher
- Institute of Metabolic Physiology, Heinrich Heine University, D-40225 Düsseldorf, Germany; Institute for Vascular and Islet Cell Biology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany
| | | | | | - Miguel Sanz
- Taros Chemicals GmbH & Co. KG, D-44227 Dortmund, Germany
| | - Haresh Ajani
- Taros Chemicals GmbH & Co. KG, D-44227 Dortmund, Germany
| | | | | | - Jens Hogeback
- A&M Labor für Analytik und Metabolismusforschung Service GmbH, D-50126 Bergheim, Germany
| | - Anke Unger
- Lead Discovery Center GmbH & Co. KG, D-44227 Dortmund, Germany
| | | | - Michelle Reina do Fundo
- German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany; Institute for Clinical Diabetology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany
| | - Bedair Dewidar
- German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany; Institute for Clinical Diabetology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany
| | - Michael Roden
- German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany; Institute for Clinical Diabetology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany; Department of Endocrinology and Diabetology, Medical Faculty and University Hospital, Heinrich Heine University, D-40225 Düsseldorf, Germany
| | - Eckhard Lammert
- Institute of Metabolic Physiology, Heinrich Heine University, D-40225 Düsseldorf, Germany; Institute for Vascular and Islet Cell Biology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich Heine University, D-40225 Düsseldorf, Germany; German Center for Diabetes Research (DZD e.V.), Partner Düsseldorf, Neuherberg, D-85764 Neuherberg, Germany.
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McClure EW, Daniels RN. Classics in Chemical Neuroscience: Dextromethorphan (DXM). ACS Chem Neurosci 2023. [PMID: 37290117 DOI: 10.1021/acschemneuro.3c00088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023] Open
Abstract
Dextromethorphan (DXM) was introduced in 1958 as the first non-opioid cough suppressant and is indicated for multiple psychiatric disorders. It has been the most used over-the-counter cough suppressant since its emergence. However, individuals quickly noticed an intoxicating and psychedelic effect if they ingested large doses. DXM's antagonism at N-methyl-d-aspartate receptors (NMDAr) is thought to underly its efficacy in treating acute cough, but supratherapeutic doses mimic the activity of dissociative hallucinogens, such as phencyclidine and ketamine. In this Review we will discuss DXM's synthesis, manufacturing information, drug metabolism, pharmacology, adverse effects, recreational use, abuse potential, and its history and importance in therapy to present DXM as a true classic in chemical neuroscience.
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Affiliation(s)
- Elliot W McClure
- Department of Pharmaceutical Sciences, Lipscomb University College of Pharmacy, Nashville, Tennessee 37204, United States
| | - R Nathan Daniels
- Department of Pharmaceutical Sciences, Union University College of Pharmacy, Jackson, Tennessee 38305, United States
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Preston FG, Riley DR, Azmi S, Alam U. Painful Diabetic Peripheral Neuropathy: Practical Guidance and Challenges for Clinical Management. Diabetes Metab Syndr Obes 2023; 16:1595-1612. [PMID: 37288250 PMCID: PMC10243347 DOI: 10.2147/dmso.s370050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Accepted: 05/16/2023] [Indexed: 06/09/2023] Open
Abstract
Painful diabetic peripheral neuropathy (PDPN) is present in nearly a quarter of people with diabetes. It is estimated to affect over 100 million people worldwide. PDPN is associated with impaired daily functioning, depression, sleep disturbance, financial instability, and a decreased quality of life. Despite its high prevalence and significant health burden, it remains an underdiagnosed and undertreated condition. PDPN is a complex pain phenomenon with the experience of pain associated with and exacerbated by poor sleep and low mood. A holistic approach to patient-centred care alongside the pharmacological therapy is required to maximise benefit. A key treatment challenge is managing patient expectation, as a good outcome from treatment is defined as a reduction in pain of 30-50%, with a complete pain-free outcome being rare. The future for the treatment of PDPN holds promise, despite a 20-year void in the licensing of new analgesic agents for neuropathic pain. There are over 50 new molecular entities reaching clinical development and several demonstrating benefit in early-stage clinical trials. We review the current approaches to its diagnosis, the tools, and questionnaires available to clinicians, international guidance on PDPN management, and existing pharmacological and non-pharmacological treatment options. We synthesise evidence and the guidance from the American Association of Clinical Endocrinology, American Academy of Neurology, American Diabetes Association, Diabetes Canada, German Diabetes Association, and the International Diabetes Federation into a practical guide to the treatment of PDPN and highlight the need for future research into mechanistic-based treatments in order to prioritise the development of personalised medicine.
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Affiliation(s)
- Frank G Preston
- Department of Cardiovascular & Metabolic Medicine, Institute of Life Course and Medical Sciences and the Pain Research Institute, University of Liverpool, Liverpool, UK
| | - David R Riley
- Department of Cardiovascular & Metabolic Medicine, Institute of Life Course and Medical Sciences and the Pain Research Institute, University of Liverpool, Liverpool, UK
| | - Shazli Azmi
- Institute of Cardiovascular Science, University of Manchester and Manchester Diabetes Centre, Manchester Foundation Trust, Manchester, UK
| | - Uazman Alam
- Department of Cardiovascular & Metabolic Medicine, Institute of Life Course and Medical Sciences and the Pain Research Institute, University of Liverpool, Liverpool, UK
- Liverpool Centre for Cardiovascular Science, University of Liverpool and Liverpool University Hospital NHS Foundation Trust, Liverpool, UK
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Combination pharmacotherapy for the treatment of neuropathic pain in adults: systematic review and meta-analysis. Pain 2023; 164:230-251. [PMID: 35588148 DOI: 10.1097/j.pain.0000000000002688] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Accepted: 03/07/2022] [Indexed: 02/06/2023]
Abstract
ABSTRACT Neuropathic pain causes substantial morbidity and healthcare utilization. Monotherapy with antidepressants or anticonvulsants often fails to provide relief. Combining different drugs sometimes provides improved analgesia and/or tolerability. More than half of patients receive 2 or more analgesics, and combination trials continue to emerge. This review comprehensively searched CENTRAL, MEDLINE, and EMBASE for relevant trials. Included studies are double-blind randomized controlled trials evaluating combinations of 2 or more drugs vs placebo or at least one monotherapy in adults with neuropathic pain. Outcomes included measures of efficacy and adverse effects. Risk of bias was assessed. Meta-analyses compared combination to monotherapy wherever 2 or more similar studies were available. Forty studies (4741 participants) were included. Studies were heterogenous with respect to various characteristics, including dose titration methods and administration (ie, simultaneous vs sequential) of the combination. Few combinations involved a nonsedating drug, and several methodological problems were identified. For opioid-antidepressant, opioid-gabapentinoid, and gabapentinoid-antidepressant combinations, meta-analyses failed to demonstrate superiority over both monotherapies. In general, adverse event profiles were not substantially different for combination therapy compared with monotherapy. Despite widespread use and a growing number of trials, convincing evidence has not yet emerged to suggest superiority of any combination over its respective monotherapies. Therefore, implementing combination therapy-as second- or third-line treatment-in situations where monotherapy is insufficient, should involve closely monitored individual dosing trials to confirm safety and overall added benefit. Further research is needed, including trials of combinations involving nonsedating agents, and to identify clinical settings and specific combinations that safely provide added benefit.
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Xu L, Sun Z, Casserly E, Nasr C, Cheng J, Xu J. Advances in Interventional Therapies for Painful Diabetic Neuropathy: A Systematic Review. Anesth Analg 2022; 134:1215-1228. [PMID: 35051958 DOI: 10.1213/ane.0000000000005860] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
BACKGROUND Painful diabetic neuropathy (PDN) is one of the major complications of diabetes mellitus. It is often debilitating and refractory to pharmaceutical therapies. Our goal was to systematically review and evaluate the strength of evidence of interventional management options for PDN and make evidence-based recommendations for clinical practice. METHODS We searched PubMed, Scopus, Google Scholar, and Cochrane Llibrary and systematically reviewed all types of clinical studies on interventional management modalities for PDN. RESULTS We identified and analyzed 10 relevant randomized clinical trials (RCTs), 8 systematic reviews/meta-analyses, and 5 observational studies of interventional modalities for PDN using pain as primary outcome. We assessed the risk of bias in grading of evidence and found that there is moderate to strong evidence to support the use of dorsal column spinal cord stimulation (SCS) in treating PDN in the lower extremities (evidence level: 1B+), while studies investigating its efficacy in the upper extremities are lacking. Evidence exists that acupuncture and injection of botulinum toxin-A provide relief in pain or muscle cramps due to PDN with minimal side effects (2B+/1B+). Similar level of evidence supports surgical decompression of lower limb peripheral nerves in patients with intractable PDN and superimposed nerve compression (2B±/1B+). Evidence for sympathetic blocks or neurolysis and dorsal root ganglion (DRG) stimulation is limited to case series (2C+). CONCLUSIONS Moderate to strong evidence exists to support the use of SCS in managing lower extremity pain in patients who have failed conventional medical management for PDN. Acupuncture or injection of botulinum toxin-A can be considered as an adjunctive therapy for PDN. Surgical decompression of peripheral nerves may be considered in patients with PDN superimposed with nerve compression. High-quality studies are warranted to further evaluate the safety, efficacy, and cost-effectiveness of interventional therapies for PDN.
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Affiliation(s)
- Li Xu
- From the Department of Anesthesiology, Chinese Academy of Medical Sciences & Peking Union Medical College Hospital, Beijing, China
| | - Zhuo Sun
- Department of Anesthesiology and Perioperative Medicine, Medical College of Georgia at Augusta University, Augusta, Georgia
| | | | | | - Jianguo Cheng
- Department of Pain Management, Anesthesiology Institute.,Department of Neuroscience, Lerner Research Institute
| | - Jijun Xu
- Department of Pain Management, Anesthesiology Institute.,Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio.,Department of Anesthesiology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio
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Sloan G, Alam U, Selvarajah D, Tesfaye S. The Treatment of Painful Diabetic Neuropathy. Curr Diabetes Rev 2022; 18:e070721194556. [PMID: 34238163 DOI: 10.2174/1573399817666210707112413] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Revised: 02/18/2021] [Accepted: 03/08/2021] [Indexed: 11/22/2022]
Abstract
Painful diabetic peripheral neuropathy (painful-DPN) is a highly prevalent and disabling condition, affecting up to one-third of patients with diabetes. This condition can have a profound impact resulting in a poor quality of life, disruption of employment, impaired sleep, and poor mental health with an excess of depression and anxiety. The management of painful-DPN poses a great challenge. Unfortunately, currently there are no Food and Drug Administration (USA) approved disease-modifying treatments for diabetic peripheral neuropathy (DPN) as trials of putative pathogenetic treatments have failed at phase 3 clinical trial stage. Therefore, the focus of managing painful- DPN other than improving glycaemic control and cardiovascular risk factor modification is treating symptoms. The recommended treatments based on expert international consensus for painful- DPN have remained essentially unchanged for the last decade. Both the serotonin re-uptake inhibitor (SNRI) duloxetine and α2δ ligand pregabalin have the most robust evidence for treating painful-DPN. The weak opioids (e.g. tapentadol and tramadol, both of which have an SNRI effect), tricyclic antidepressants such as amitriptyline and α2δ ligand gabapentin are also widely recommended and prescribed agents. Opioids (except tramadol and tapentadol), should be prescribed with caution in view of the lack of definitive data surrounding efficacy, concerns surrounding addiction and adverse events. Recently, emerging therapies have gained local licenses, including the α2δ ligand mirogabalin (Japan) and the high dose 8% capsaicin patch (FDA and Europe). The management of refractory painful-DPN is difficult; specialist pain services may offer off-label therapies (e.g. botulinum toxin, intravenous lidocaine and spinal cord stimulation), although there is limited clinical trial evidence supporting their use. Additionally, despite combination therapy being commonly used clinically, there is little evidence supporting this practise. There is a need for further clinical trials to assess novel therapeutic agents, optimal combination therapy and existing agents to determine which are the most effective for the treatment of painful-DPN. This article reviews the evidence for the treatment of painful-DPN, including emerging treatment strategies such as novel compounds and stratification of patients according to individual characteristics (e.g. pain phenotype, neuroimaging and genotype) to improve treatment responses.
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Affiliation(s)
- Gordon Sloan
- Diabetes Research Unit, Royal Hallamshire Hospital, Sheffield Teaching Hospitals, NHS Foundation Trust, Sheffield, UK
| | - Uazman Alam
- Department of Cardiovascular and Metabolic Medicine and the Pain Research Institute, Institute of Life Course and Medical Sciences, University of Liverpool, and Liverpool University Hospital, NHS Foundation Trust, Liverpool, UK
- Division of Diabetes, Endocrinology and Gastroenterology, Institute of Human Development, University of Manchester, Manchester, UK
| | - Dinesh Selvarajah
- Diabetes Research Unit, Royal Hallamshire Hospital, Sheffield Teaching Hospitals, NHS Foundation Trust, Sheffield, UK
- Department of Oncology and Human Metabolism, University of Sheffield, Sheffield, UK
| | - Solomon Tesfaye
- Diabetes Research Unit, Royal Hallamshire Hospital, Sheffield Teaching Hospitals, NHS Foundation Trust, Sheffield, UK
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Serrano Afonso A, Carnaval T, Videla Cés S. Combination Therapy for Neuropathic Pain: A Review of Recent Evidence. J Clin Med 2021; 10:jcm10163533. [PMID: 34441829 PMCID: PMC8396869 DOI: 10.3390/jcm10163533] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Revised: 07/31/2021] [Accepted: 08/09/2021] [Indexed: 12/19/2022] Open
Abstract
Pharmacological treatment is not very effective for neuropathic pain (NP). A progressive decrease in the estimated effect of NP drugs has been reported, giving rise to an increase in the use of the multimodal analgesic approach. We performed a new independent review to assess whether more and better-quality evidence has become available since the last systematic review. We evaluated the efficacy, tolerability, and safety of double-blinded randomized controlled trials involving only adult participants and comparing combination therapy (CT: ≥2 drugs) with a placebo and/or at least one other comparator with an NP indication. The primary outcome assessed was the proportion of participants reporting ≥50% pain reductions from baseline. The secondary outcome assessed was the proportion of drop-outs due to treatment-emergent adverse events. After removing duplicates, 2323 citations were screened, with 164 articles assessed for eligibility, from which 16 were included for qualitative analysis. From the latter, only five lasted for at least 12 weeks and only six complied with the required data for complete analysis. CT has been adopted for years without robust evidence. Efforts have been made to achieve better-quality evidence, but the quality has not improved over the years. In this regard, guidelines for NP should attempt to make recommendations about CT research, prioritizing which combinations to analyze.
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Affiliation(s)
- Ancor Serrano Afonso
- Department of Anesthesiology, Resuscitation and Pain Management, Hospital Universitari de Bellvitge, 08907 L’Hospitalet de Llobregat, Spain
- Correspondence:
| | - Thiago Carnaval
- Department of Clinical Pharmacology, Hospital Universitari de Bellvitge, 08907 L’Hospitalet de Llobregat, Spain;
| | - Sebastià Videla Cés
- Pharmacology Unit, Department of Pathology and Experimental Therapeutics, School of Medicine and Health Sciences, IDIBELL, University of Barcelona, 08907 L’Hospitalet de Llobregat, Spain;
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Abstract
BACKGROUND Diabetic neuropathy is a multifaceted condition affecting up to 50% of individuals with long standing diabetes. The most common presentation is peripheral diabetic sensory neuropathy (DPN). METHODS We carried out a systematic review of papers dealing with diabetic neuropathy on Pubmed in addition to a targeted Google search.Search terms included small fiber neuropathy,diffuse peripheral neuropathy, quantitative sensory testing, nerve conduction testing, intra-epidermal nerve fiber density, corneal confocal reflectance microscopy, aldose reductase inhbitors, nerve growth factor, alpha-lipoic acid, ruboxistaurin, nerve growth factor antibody, and cibinetide. RESULTS Over the past half century, there have been a number of agents undergoing unsuccessful trials for treatment of DPN.There are several approved agents for relief of pain caused by diabetic neuropathy, but these do not affect the pathologic process. EXPERT OPINION The failure to find treatments for diabetic neuropathy can be ascribed to (1) the complexity of design of studies and (2) the slow progression of the condition, necessitating long duration trials to prove efficacy.We propose a modification of the regulatory process to permit early introduction of agents with demonstrated safety and suggestion of benefit as well as prolongation of marketing exclusivity while long term trials are in progress to prove efficacy.
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Affiliation(s)
- Marc S Rendell
- The Association for Diabetes Investigators , Newport Coast, California. USA
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Liampas A, Rekatsina M, Vadalouca A, Paladini A, Varrassi G, Zis P. Pharmacological Management of Painful Peripheral Neuropathies: A Systematic Review. Pain Ther 2020; 10:55-68. [PMID: 33145709 PMCID: PMC8119529 DOI: 10.1007/s40122-020-00210-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 10/08/2020] [Indexed: 12/28/2022] Open
Abstract
Introduction Peripheral neuropathic pain (PNP) arises either acutely or in the chronic phase of a lesion or disease of the peripheral nervous system and is associated with a notable disease burden. The management of PNP is often challenging. The aim of this systematic review was to evaluate current evidence, derived from randomized controlled trials (RCTs) that have assessed pharmacological interventions for the treatment of PNP due to polyneuropathy (PN). Methods A systematic search of the PubMed database led to the identification of 538 papers, of which 457 were excluded due to not meeting the eligibility criteria, and two articles were identified through screening of the reference lists of the 81 eligible studies. Ultimately, 83 papers were included in this systematic review. Results The best available evidence for the management of painful diabetic polyneuropathy (DPN) is for amitriptyline, duloxetine, gabapentin, pregabalin and venlafaxine as monotherapies and oxycodone as add-on therapy (level II of evidence). Tramadol appears to be effective when used as a monotherapy and add-on therapy in patients with PN of various etiologies (level II of evidence). Weaker evidence (level III) is available on the effectiveness of several other agents discussed in this review for the management of PNP due to PN. Discussion Response to treatment may be affected by the underlying pathophysiological mechanisms that are involved in the pathogenesis of the PN and, therefore, it is very important to thoroughly investigate patients presenting with PNP to determine the causes of this neuropathy. Future RCTs should be conducted to shed more light on the use of pharmacological approaches in patients with other forms of PNP and to design specific treatment algorithms. Electronic supplementary material The online version of this article (10.1007/s40122-020-00210-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | - Athina Vadalouca
- Pain and Palliative Care Center, Athens Medical Center, Athens, Greece
| | - Antonella Paladini
- Department of Life, Health and Environmental Sciences (MESVA), University of L'Aquila, L'Aquila, Italy
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Azmi S, Alam U, Burgess J, Malik RA. State-of-the-art pharmacotherapy for diabetic neuropathy. Expert Opin Pharmacother 2020; 22:55-68. [PMID: 32866410 DOI: 10.1080/14656566.2020.1812578] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
INTRODUCTION The global epidemic of diabetes has led to an epidemic of diabetes complications. Diabetic neuropathy is the most common microvascular complication, of which diabetic peripheral neuropathy (DPN) and autonomic neuropathy (AN) are the most prevalent, affecting ~50% of patients. DPN results in pain with a poor quality of life and a loss of sensation with an increased risk of foot ulceration. Autonomic neuropathy can cause significant morbidity in a minority and is associated with increased mortality. The cornerstone of treatment to prevent or limit the progression of DPN/AN is multifactorial risk factor modification including treatment of glycemia, lipids and blood pressure. Whilst, there are no FDA-approved disease-modifying therapies, there are a number of therapies to relieve symptoms in DPN and AN. AREAS COVERED The authors discuss current approved therapies for painful diabetic neuropathy and autonomic neuropathy. They also address the potential role of improving risk factors to limit the development and progression of diabetic neuropathy and new pathogenetic and pain-relieving treatments. EXPERT OPINION The FDA-approved Pregabalin and Duloxetine over 25 years ago and Tapentadol, 6 years ago for painful diabetic neuropathy. There are currently no FDA-approved disease-modifying treatments for diabetic neuropathy which has been attributed to inappropriate models of the disease with limited translational capacity and major limitations of trial designs and endpoints in clinical trials.
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Affiliation(s)
- Shazli Azmi
- Institute of Cardiovascular Science, University of Manchester and Manchester NHS Foundation Trust , Manchester, UK
| | - Uazman Alam
- Division of Diabetes, Endocrinology and Gastroenterology, Institute of Human Development, University of Manchester , Manchester, UK.,Department of Cardiovascular & Metabolic Medicine, Institute of Life Course and Medical Sciences, University of Liverpool , Liverpool, UK.,Department of Diabetes and Endocrinology, Liverpool University Hospital NHS Foundation Trust , Liverpool, UK
| | - Jamie Burgess
- Department of Cardiovascular & Metabolic Medicine, Institute of Life Course and Medical Sciences, University of Liverpool , Liverpool, UK
| | - Rayaz A Malik
- Department of Medicine, Weill Cornell Medicine-Qatar , Doha, Qatar
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Røikjer J, Mørch CD, Ejskjaer N. Diabetic Peripheral Neuropathy: Diagnosis and Treatment. Curr Drug Saf 2020; 16:2-16. [PMID: 32735526 DOI: 10.2174/1574886315666200731173113] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 06/04/2020] [Accepted: 06/16/2020] [Indexed: 02/08/2023]
Abstract
BACKGROUND Diabetic peripheral neuropathy (DPN) is traditionally divided into large and small fibre neuropathy (SFN). Damage to the large fibres can be detected using nerve conduction studies (NCS) and often results in a significant reduction in sensitivity and loss of protective sensation, while damage to the small fibres is hard to reliably detect and can be either asymptomatic, associated with insensitivity to noxious stimuli, or often manifests itself as intractable neuropathic pain. OBJECTIVE To describe the recent advances in both detection, grading, and treatment of DPN as well as the accompanying neuropathic pain. METHODS A review of relevant, peer-reviewed, English literature from MEDLINE, EMBASE and Cochrane Library between January 1st 1967 and January 1st 2020 was used. RESULTS We identified more than three hundred studies on methods for detecting and grading DPN, and more than eighty randomised-controlled trials for treating painful diabetic neuropathy. CONCLUSION NCS remains the method of choice for detecting LFN in people with diabetes, while a gold standard for the detection of SFN is yet to be internationally accepted. In the recent years, several methods with huge potential for detecting and grading this condition have become available including skin biopsies and corneal confocal microscopy, which in the future could represent reliable endpoints for clinical studies. While several newer methods for detecting SFN have been developed, no new drugs have been accepted for treating neuropathic pain in people with diabetes. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors and anticonvulsants remain first line treatment, while newer agents targeting the proposed pathophysiology of DPN are being developed.
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Affiliation(s)
- Johan Røikjer
- Department of Health Science and Technology, Aalborg University Hospital, Aalborg University, Aalborg, Denmark
| | - Carsten Dahl Mørch
- Department of Health Science and Technology, Aalborg University Hospital, Aalborg University, Aalborg, Denmark
| | - Niels Ejskjaer
- Department of Clinical Medicine, Aalborg University, Aalborg, Denmark
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Alam U, Sloan G, Tesfaye S. Treating Pain in Diabetic Neuropathy: Current and Developmental Drugs. Drugs 2020; 80:363-384. [DOI: 10.1007/s40265-020-01259-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Martin E, Sorel M, Morel V, Marcaillou F, Picard P, Delage N, Tiberghien F, Crosmary MC, Najjar M, Colamarino R, Créach C, Lietar B, Brumauld de Montgazon G, Margot-Duclot A, Loriot MA, Narjoz C, Lambert C, Pereira B, Pickering G. Dextromethorphan and memantine after ketamine analgesia: a randomized control trial. DRUG DESIGN DEVELOPMENT AND THERAPY 2019; 13:2677-2688. [PMID: 31447547 PMCID: PMC6683947 DOI: 10.2147/dddt.s207350] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/02/2019] [Accepted: 06/05/2019] [Indexed: 01/05/2023]
Abstract
Purpose Intravenous ketamine is often prescribed in severe neuropathic pain. Oral N-methyl-D-aspartate receptor (NMDAR) antagonists might prolong pain relief, reducing the frequency of ketamine infusions and hospital admissions. This clinical trial aimed at assessing whether oral dextromethorphan or memantine might prolong pain relief after intravenous ketamine. Patients and methods A multicenter randomized controlled clinical trial included 60 patients after ketamine infusion for refractory neuropathic pain. Dextromethorphan (90 mg/day), memantine (20 mg/day) or placebo was given for 12 weeks (n=20 each) after ketamine infusion. The primary endpoint was pain intensity at one month. Secondary endpoints included pain, sleep, anxiety, depression, cognitive function and quality of life evaluations up to 12 weeks. Results At 1 month, dextromethorphan maintained ketamine pain relief (Numeric Pain Scale: 4.01±1.87 to 4.05±2.61, p=0.53) and diminished pain paroxysms (p=0.03) while pain intensity increased significantly with memantine and placebo (p=0.04). At 3 months, pain remained lower than at inclusion (p=0.001) and was not significantly different in the three groups. Significant benefits were observed on cognitive-affective domains and quality of life for dextromethorphan and memantine (p<0.05). Conclusions Oral dextromethorphan given after ketamine infusion extends pain relief during one month and could help patients to better cope with pain. Future studies should include larger populations stratified on pharmacogenetics screening. Optimization of an oral drug that could extend ketamine antihyperalgesia, with fewer hospital admissions, remains a prime challenge in refractory neuropathic pain.
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Affiliation(s)
- Elodie Martin
- Université Clermont Auvergne, Pharmacologie Fondamentale Et Clinique de la Douleur, Neuro-Dol, Inserm 1107, F-63000 Clermont-Ferrand, France
| | - Marc Sorel
- Centre D'evaluation et de Traitement de la Douleur/soins Palliatifs, Nemours, France
| | - Véronique Morel
- CHU Clermont-Ferrand, Centre de Pharmacologie Clinique/Centre d'investigation Clinique Inserm 1405, F-63003 Clermont-Ferrand cedex, France
| | - Fabienne Marcaillou
- Centre d'Evaluation et de Traitement de la Douleur, CHU de Clermont-Ferrand, France
| | - Pascale Picard
- Centre d'Evaluation et de Traitement de la Douleur, CHU de Clermont-Ferrand, France
| | - Noémie Delage
- Centre d'Evaluation et de Traitement de la Douleur, CHU de Clermont-Ferrand, France
| | - Florence Tiberghien
- Centre d'evaluation et de Traitement de la Douleur/soins Palliatifs, CHU Jean Minjoz, Besançon, France
| | | | - Mitra Najjar
- Centre d'evaluation et de Traitement de la Douleur, CH Jacques Lacarin Vichy, France
| | - Renato Colamarino
- Centre d'evaluation et de Traitement de la Douleur, CH Jacques Lacarin Vichy, France
| | - Christelle Créach
- Centre d'evaluation et de Traitement de la Douleur, CHU de Saint-etienne, France.,Inserm U1028 & Umr 5292, Centre de Neurosciences de Lyon, Université Lyon & Jean-monnet De Saint-etienne, France
| | - Béatrice Lietar
- Centre d'evaluation et de Traitement de la Douleur, CHU de Saint-etienne, France
| | | | - Anne Margot-Duclot
- Centre d'evaluation et de Traitement de la Douleur, Fondation A de Rothschild, Paris, France
| | - Marie-Anne Loriot
- Service de biochimie, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France.,Inserm UMR-S 1147, Université Paris Descartes, Paris, France
| | - Céline Narjoz
- Service de biochimie, Hôpital Européen Georges Pompidou, Assistance Publique Hôpitaux de Paris, Paris, France.,Inserm UMR-S 1147, Université Paris Descartes, Paris, France
| | - Céline Lambert
- CHU Clermont-Ferrand, Délégation Recherche Clinique & Innovation - Villa annexe IFSI, 58 Rue Montalembert, F-63003 Clermont-Ferrand cedex, France
| | - Bruno Pereira
- CHU Clermont-Ferrand, Délégation Recherche Clinique & Innovation - Villa annexe IFSI, 58 Rue Montalembert, F-63003 Clermont-Ferrand cedex, France
| | - Gisèle Pickering
- Université Clermont Auvergne, Pharmacologie Fondamentale Et Clinique de la Douleur, Neuro-Dol, Inserm 1107, F-63000 Clermont-Ferrand, France.,CHU Clermont-Ferrand, Centre de Pharmacologie Clinique/Centre d'investigation Clinique Inserm 1405, F-63003 Clermont-Ferrand cedex, France
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Martin E, Narjoz C, Decleves X, Labat L, Lambert C, Loriot MA, Ducheix G, Dualé C, Pereira B, Pickering G. Dextromethorphan Analgesia in a Human Experimental Model of Hyperalgesia. Anesthesiology 2019; 131:356-368. [DOI: 10.1097/aln.0000000000002736] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Abstract
Editor’s Perspective
What We Already Know about This Topic
What This Article Tells Us That Is New
Background
Central pain sensitization is often refractory to drug treatment. Dextromethorphan, an N-methyl-d-aspartate receptor antagonist, is antihyperalgesic in preclinical pain models. The hypothesis is that dextromethorphan is also antihyperalgesic in humans.
Methods
This randomized, double-blind, placebo-controlled, crossover study explores the antihyperalgesic effect of single and repeated 30-mg dose of oral dextromethorphan in 20 volunteers, using the freeze-injury pain model. This model leads to development of primary and secondary hyperalgesia, which develops away from the site of injury and is associated with central sensitization and activation of N-methyl-d-aspartate receptor in the spinal cord. The primary outcome was antihyperalgesia calculated with the area under the curve of the percentage change in mechanical pain threshold (electronic von Frey) on the area of secondary hyperalgesia. The secondary outcomes were mechanical pain threshold on the area of primary hyperalgesia and cognitive (reaction time) effect.
Results
Single 30-mg results are reported. Antihyperalgesia (% · min) is significantly higher on the area of secondary hyperalgesia with dextromethorphan than placebo (median [interquartile range]: 3,029 [746; 6,195] vs. 710 [–3,248; 4,439], P = 0.009, Hedge’s g = 0.8, 95% CI [0.1; 1.4]). On primary hyperalgesia area, mechanical pain threshold 2 h after drug intake is significantly higher with dextromethorphan (P = 0.011, Hedge’s g = 0.63, 95% CI [0.01; 1.25]). No difference in antinociception is observed after thermal painful stimuli on healthy skin between groups. Reaction time (ms) is shorter with placebo than with dextromethorphan (median [interquartile range]: 21.6 [–37.4; 0.1] vs. –1.2 [–24.3; 15.4], P = 0.015, Hedge’s g = 0.75, 95% CI [0.12; 1.39]). Nonserious adverse events occurrence (15%, 3 of 20 volunteers) was similar in both groups.
Conclusions
This study shows that low-dose (30-mg) dextromethorphan is antihyperalgesic in humans on the areas of primary and secondary hyperalgesia and reverses peripheral and central neuronal sensitization. Because dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-d-aspartate receptor may need to be sensitized by pain for dextromethorphan to be effective.
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Affiliation(s)
- E. Martin
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - C. Narjoz
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - X. Decleves
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - L. Labat
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - C. Lambert
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - M.-A. Loriot
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - G. Ducheix
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - C. Dualé
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - B. Pereira
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
| | - G. Pickering
- From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.); Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.); University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.); Assistance Publique—Paris Hospital (AP-HP), Georges Pompidou European Hospital,
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Dextromethorphan/Quinidine in Migraine Prophylaxis: An Open-label Observational Clinical Study. Clin Neuropharmacol 2018; 41:64-69. [DOI: 10.1097/wnf.0000000000000272] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Wilson LM, Sharma R, Dy SM, Waldfogel JM, Robinson KA. Searching ClinicalTrials.gov did not change the conclusions of a systematic review. J Clin Epidemiol 2017; 90:127-135. [PMID: 28757261 DOI: 10.1016/j.jclinepi.2017.07.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 06/27/2017] [Accepted: 07/07/2017] [Indexed: 10/19/2022]
Abstract
OBJECTIVES We assessed the effect of searching ClinicalTrials.gov on the conclusions of a systematic review. STUDY DESIGN AND SETTING We conducted this case study concurrently with a systematic review. We searched ClinicalTrials.gov on March 9, 2016, to identify trial records eligible for inclusion in the review. Two independent reviewers screened ClinicalTrials.gov records. We compared conclusions and strength of evidence grade with and without ClinicalTrials.gov records for 31 comparisons and 2 outcomes. RESULTS We identified 106 trials (53 in the peer-reviewed literature only, 23 in ClinicalTrials.gov only, and 30 in both sources). For one comparison, the addition of results identified through ClinicalTrials.gov reduced the pooled effect size. We found evidence of selective outcome reporting for two comparisons and suspected publication bias for another two comparisons. For all other comparisons, searching ClinicalTrials.gov did not change conclusions or the strength of evidence grading for the two outcomes. CONCLUSION Our search of ClinicalTrials.gov bolstered suspicions of reporting biases but did not change either the conclusions or the strength of evidence grading. Further research is needed to determine the effect of searching ClinicalTrials.gov on the conclusions of systematic reviews in different topic areas and as the new rules for registration of trial results take effect.
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Affiliation(s)
- Lisa M Wilson
- Department of Health Policy and Management, Johns Hopkins University Bloomberg School of Public Health, 624 N. Broadway, 6th Floor, Baltimore, MD 21205, USA.
| | - Ritu Sharma
- Department of Health Policy and Management, Johns Hopkins University Bloomberg School of Public Health, 624 N. Broadway, 6th Floor, Baltimore, MD 21205, USA
| | - Sydney M Dy
- Department of Health Policy and Management, Johns Hopkins University Bloomberg School of Public Health, 624 N. Broadway, 6th Floor, Baltimore, MD 21205, USA
| | - Julie M Waldfogel
- Department of Pharmacy, Johns Hopkins Hospital, 1800 Orleans Street, Carnegie 180, Baltimore, MD 21287, USA
| | - Karen A Robinson
- Department of Medicine, Johns Hopkins University School of Medicine, 1830 E. Monument Street, 8th Floor, Baltimore, MD 21205, USA
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Pharmacological Management of Neuropathic Pain: Current Trends and Possible Approaches. ARCHIVES OF NEUROSCIENCE 2016. [DOI: 10.5812/archneurosci.28998] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Taylor CP, Traynelis SF, Siffert J, Pope LE, Matsumoto RR. Pharmacology of dextromethorphan: Relevance to dextromethorphan/quinidine (Nuedexta®) clinical use. Pharmacol Ther 2016; 164:170-82. [PMID: 27139517 DOI: 10.1016/j.pharmthera.2016.04.010] [Citation(s) in RCA: 104] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Dextromethorphan (DM) has been used for more than 50years as an over-the-counter antitussive. Studies have revealed a complex pharmacology of DM with mechanisms beyond blockade of N-methyl-d-aspartate (NMDA) receptors and inhibition of glutamate excitotoxicity, likely contributing to its pharmacological activity and clinical potential. DM is rapidly metabolized to dextrorphan, which has hampered the exploration of DM therapy separate from its metabolites. Coadministration of DM with a low dose of quinidine inhibits DM metabolism, yields greater bioavailability and enables more specific testing of the therapeutic properties of DM apart from its metabolites. The development of the drug combination DM hydrobromide and quinidine sulfate (DM/Q), with subsequent approval by the US Food and Drug Administration for pseudobulbar affect, led to renewed interest in understanding DM pharmacology. This review summarizes the interactions of DM with brain receptors and transporters and also considers its metabolic and pharmacokinetic properties. To assess the potential clinical relevance of these interactions, we provide an analysis comparing DM activity from in vitro functional assays with the estimated free drug DM concentrations in the brain following oral DM/Q administration. The findings suggest that DM/Q likely inhibits serotonin and norepinephrine reuptake and also blocks NMDA receptors with rapid kinetics. Use of DM/Q may also antagonize nicotinic acetylcholine receptors, particularly those composed of α3β4 subunits, and cause agonist activity at sigma-1 receptors.
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Affiliation(s)
| | - Stephen F Traynelis
- Dept. of Pharmacology, Emory University School of Medicine, Atlanta, GA, USA
| | - Joao Siffert
- Avanir Pharmaceuticals, Inc., Aliso Viejo, CA, USA
| | - Laura E Pope
- Avanir Pharmaceuticals, Inc., Aliso Viejo, CA, USA
| | - Rae R Matsumoto
- College of Pharmacy, Touro University California, Vallejo, CA, USA
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Abstract
Many drugs are carbon-based, and carbon-hydrogen bonding is particularly relevant for understanding important properties of drug molecules. Deuteration refers to the selective replacement of protium hydrogen isotope atoms in small-molecule drugs with deuterium hydrogen isotope atoms. Deuteration of a drug is most likely to affect pharmacokinetic properties, such as metabolism, rather than its pharmacodynamic effects. For this reason, the metabolism of certain drugs may be favorably influenced when deuterium is substituted for protium, resulting in improved safety, tolerability, or efficacy. Examples of deuterated drugs that have been evaluated in clinical studies include paroxetine, tetrabenazine, and dextromethorphan.
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Nguyen L, Thomas KL, Lucke-Wold BP, Cavendish JZ, Crowe MS, Matsumoto RR. Dextromethorphan: An update on its utility for neurological and neuropsychiatric disorders. Pharmacol Ther 2016; 159:1-22. [PMID: 26826604 DOI: 10.1016/j.pharmthera.2016.01.016] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Dextromethorphan (DM) is a commonly used antitussive and is currently the only FDA-approved pharmaceutical treatment for pseudobulbar affect. Its safety profile and diverse pharmacologic actions in the central nervous system have stimulated new interest for repurposing it. Numerous preclinical investigations and many open-label or blinded clinical studies have demonstrated its beneficial effects across a variety of neurological and psychiatric disorders. However, the optimal dose and safety of chronic dosing are not fully known. This review summarizes the preclinical and clinical effects of DM and its putative mechanisms of action, focusing on depression, stroke, traumatic brain injury, seizure, pain, methotrexate neurotoxicity, Parkinson's disease and autism. Moreover, we offer suggestions for future research with DM to advance the treatment for these and other neurological and psychiatric disorders.
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Affiliation(s)
- Linda Nguyen
- Department of Behavioral Medicine and Psychiatry, School of Medicine, West Virginia University, Morgantown, WV 26506, USA; Department of Pharmaceutical Sciences, School of Pharmacy, West Virginia University, Morgantown, WV 26506, USA
| | - Kelan L Thomas
- College of Pharmacy, Touro University California, Vallejo, CA 94592, USA
| | - Brandon P Lucke-Wold
- Graduate Program in Neuroscience, School of Medicine, West Virginia University, Morgantown, WV 26506, USA
| | - John Z Cavendish
- Graduate Program in Neuroscience, School of Medicine, West Virginia University, Morgantown, WV 26506, USA
| | - Molly S Crowe
- Department of Psychology, West Virginia University, Morgantown, WV 26506, USA
| | - Rae R Matsumoto
- Department of Behavioral Medicine and Psychiatry, School of Medicine, West Virginia University, Morgantown, WV 26506, USA; College of Pharmacy, Touro University California, Vallejo, CA 94592, USA.
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Martin E, Morel V, Joly D, Villatte C, Delage N, Dubray C, Pereira B, Pickering G. Rationale and design of a randomized double-blind clinical trial in breast cancer: dextromethorphan in chemotherapy-induced peripheral neuropathy. Contemp Clin Trials 2015; 41:146-51. [PMID: 25636304 DOI: 10.1016/j.cct.2015.01.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 01/18/2015] [Accepted: 01/20/2015] [Indexed: 12/18/2022]
Abstract
BACKGROUND Anti-cancer chemotherapy often induces peripheral neuropathy and consequent cognitive and quality of life impairment. Guidelines recommend antiepileptics or antidepressants but their efficacy is limited.Dextromethorphan, a N-methyl-D-aspartate receptor antagonist, has shown its efficacy in painful diabetic neuropathy and in post-operative pain but has not been studied in chemotherapy-induced peripheral neuropathy. This clinical trial evaluates the effect of dextromethorphan on pain, cognition and quality of life in patients who suffer from neuropathic pain induced by chemotherapy for breast cancer. It also assesses the impact of dextromethorphan genetic polymorphism on analgesia. METHODS AND DESIGN This trial is a randomized, placebo-controlled, double-blind clinical study in two parallel groups (NCT02271893). It includes 40 breast cancer patients suffering from chemotherapy-induced peripheral neuropathy. They are randomly allocated to dextromethorphan (maximal dose 90 mg/day) or placebo for 4 weeks. The primary endpoint is pain intensity measured after 4 weeks of treatment on a (0-10) Numeric Pain Rating Scale. Secondary outcomes include assessment of neuropathic pain, cognitive function, anxiety/depression, sleep and quality of life. Data analysis is performed using mixed models and the tests are two-sided, with a type I error set at α=0.05. DISCUSSION Considering the poor efficacy of available drugs in chemotherapy-induced neuropathic pain, dextromethorphan may be a valuable therapeutic option. Pharmacogenetics may provide predictive factors of dextromethorphan response in patients suffering from breast cancer.
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Affiliation(s)
- Elodie Martin
- Clermont Université, Laboratoire de Pharmacologie, Faculté de médecine, F-63001 Clermont-Ferrand, France; Inserm, CIC 1405, UMR Neurodol 1107, F-63003 Clermont-Ferrand, France
| | - Véronique Morel
- Inserm, CIC 1405, UMR Neurodol 1107, F-63003 Clermont-Ferrand, France; CHU Clermont-Ferrand, Centre de Pharmacologie Clinique, F-63003 Clermont-Ferrand, France
| | - Dominique Joly
- Centre Jean Perrin, Centre de Lutte contre le Cancer, CHU Clermont-Ferrand, F-63000 Clermont-Ferrand, France
| | - Christine Villatte
- Centre Jean Perrin, Centre de Lutte contre le Cancer, CHU Clermont-Ferrand, F-63000 Clermont-Ferrand, France
| | - Noémie Delage
- CHU Clermont-Ferrand, Centre d'Evaluation et de Traitement de la Douleur, F-63003 Clermont-Ferrand, France
| | - Claude Dubray
- Clermont Université, Laboratoire de Pharmacologie, Faculté de médecine, F-63001 Clermont-Ferrand, France; Inserm, CIC 1405, UMR Neurodol 1107, F-63003 Clermont-Ferrand, France; CHU Clermont-Ferrand, Centre de Pharmacologie Clinique, F-63003 Clermont-Ferrand, France
| | - Bruno Pereira
- CHU Clermont-Ferrand, Délégation Recherche Clinique & Innovation-Villa annexe IFSI, 58 Rue Montalembert, F-63003 Clermont-Ferrand cedex, France
| | - Gisèle Pickering
- Clermont Université, Laboratoire de Pharmacologie, Faculté de médecine, F-63001 Clermont-Ferrand, France; Inserm, CIC 1405, UMR Neurodol 1107, F-63003 Clermont-Ferrand, France; CHU Clermont-Ferrand, Centre de Pharmacologie Clinique, F-63003 Clermont-Ferrand, France.
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Weinbroum AA, Zur E. Patient-Tailored Combinations of Systemic and Topical Preparations for Localized Peripheral Neuropathic Pain: A Two-Case Report. J Pain Palliat Care Pharmacother 2015; 29:27-33. [DOI: 10.3109/15360288.2014.997852] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Arakawa A, Kaneko M, Narukawa M. An Investigation of Factors Contributing to Higher Levels of Placebo Response in Clinical Trials in Neuropathic Pain: A Systematic Review and Meta-Analysis. Clin Drug Investig 2015; 35:67-81. [DOI: 10.1007/s40261-014-0259-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Javed S, Petropoulos IN, Alam U, Malik RA. Treatment of painful diabetic neuropathy. Ther Adv Chronic Dis 2015; 6:15-28. [PMID: 25553239 DOI: 10.1177/2040622314552071] [Citation(s) in RCA: 122] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Painful diabetic neuropathy (PDN) is a debilitating consequence of diabetes that may be present in as many as one in five patients with diabetes. The objective assessment of PDN is difficult, making it challenging to diagnose and assess in both clinical practice and clinical trials. No single treatment exists to prevent or reverse neuropathic changes or to provide total pain relief. Treatment of PDN is based on three major approaches: intensive glycaemic control and risk factor management, treatments based on pathogenetic mechanisms, and symptomatic pain management. Clinical guidelines recommend pain relief in PDN through the use of antidepressants such as amitriptyline and duloxetine, the γ-aminobutyric acid analogues gabapentin and pregabalin, opioids and topical agents such as capsaicin. Of these medications, duloxetine and pregabalin were approved by the US Food and Drug Administration (FDA) in 2004 and tapentadol extended release was approved in 2012 for the treatment of PDN. Proposed pathogenetic treatments include α-lipoic acid (stems reactive oxygen species formation), benfotiamine (prevents vascular damage in diabetes) and aldose-reductase inhibitors (reduces flux through the polyol pathway). There is a growing need for studies to evaluate the most potent drugs or combinations for the management of PDN to maximize pain relief and improve quality of life. A number of agents are potential candidates for future use in PDN therapy, including Nav 1.7 antagonists, N-type calcium channel blockers, NGF antibodies and angiotensin II type 2 receptor antagonists.
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Affiliation(s)
- Saad Javed
- Centre for Endocrinology and Diabetes, University of Manchester, Core Technology Facility (3rd floor), 46 Grafton Street, Manchester, M13 9NT, UK
| | - Ioannis N Petropoulos
- School of Medicine, Institute of Human Development, Centre for Endocrinology and Diabetes, Manchester, UK
| | - Uazman Alam
- School of Medicine, Institute of Human Development, Centre for Endocrinology and Diabetes, and Central Manchester NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK
| | - Rayaz A Malik
- School of Medicine, Institute of Human Development, Centre for Endocrinology and Diabetes, Central Manchester NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK, and Weill Cornell Medical College, Qatar
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Ferrara JM. CRPS-related neurogenic edema responsive to dextromethorphan/quinidine. PAIN MEDICINE 2014; 15:1981-3. [PMID: 25139080 DOI: 10.1111/pme.12539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Joseph M Ferrara
- Department of Medicine, Division of Neurology, Virginia Tech Carilion School of Medicine and Research Institute, Roanoke, Virginia, USA
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Rationale and design of a multicenter randomized clinical trial with memantine and dextromethorphan in ketamine-responder patients. Contemp Clin Trials 2014; 38:314-20. [PMID: 24948402 DOI: 10.1016/j.cct.2014.06.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2014] [Revised: 06/03/2014] [Accepted: 06/05/2014] [Indexed: 01/29/2023]
Abstract
The N-methyl-D-aspartate receptor plays an important role in central sensitization of neuropathic pain and N-methyl-D-aspartate receptor antagonists, such as ketamine, memantine and dextromethorphan may be used for persistent pain. However, ketamine cannot be repeated too often because of its adverse events. A drug relay would be helpful in the outpatient to postpone or even cancel the next ketamine infusion. This clinical trial evaluates if memantine and/or dextromethorphan given as a relay to ketamine responders may maintain or induce a decrease of pain intensity and have a beneficial impact on cognition and quality of life. This trial is a multi-center, randomized, controlled and single-blind clinical study (NCT01602185). It includes 60 ketamine responder patients suffering from neuropathic pain. They are randomly allocated to memantine, dextromethorphan or placebo. After ketamine infusion, 60 patients received either memantine (maximal dose 20 mg/day), or dextromethorphan (maximal dose 90 mg/day), or placebo for 12 weeks. The primary endpoint is pain measured on a (0-10) Numeric Rating Scale 1 month after inclusion. Secondary outcomes include assessment of neuropathic pain, sleep, quality of life, anxiety/depression and cognitive function at 2 and 3 months. Data analysis is performed using mixed models and the tests are two-sided, with a type I error set at α=0.05. This study will explore if oral memantine and/or dextromethorphan may be a beneficial relay in ketamine responders and may diminish ketamine infusion frequency. Preservation of cognitive function and quality of life is also a central issue that will be analyzed in these vulnerable patients.
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Morel V, Pickering G, Etienne M, Dupuis A, Privat AM, Chalus M, Eschalier A, Daulhac L. Low doses of dextromethorphan have a beneficial effect in the treatment of neuropathic pain. Fundam Clin Pharmacol 2014; 28:671-80. [PMID: 24702319 DOI: 10.1111/fcp.12076] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 03/20/2014] [Accepted: 04/01/2014] [Indexed: 12/30/2022]
Abstract
N-methyl-D-aspartate receptor (NMDAR) antagonists may be given in persistent neuropathic pain, but adverse events especially with ketamine may limit their clinical use. Less central and cognitive adverse events are described with dextromethorphan and memantine. These molecules have been explored in many preclinical and clinical studies, but data are conflicting as regards neuropathic pain alleviation. Dextromethorphan and memantine have been administered to animals after spinal nerve ligation (SNL) to evaluate their antinociceptive/cognitive effects and associated molecular events, including the phosphorylation of several tyrosine (pTyr(1336), pTyr(1472)) residues in the NR2B NMDAR subunit. Spinal nerve ligation and sham animals received dextromethorphan (10 mg/kg, i.p.), memantine (20 mg/kg, i.p.) or saline (1 mL/kg, i.p.). These drugs were administered once symptoms of allodynia and hyperalgesia had developed. Tests were carried out before and after surgery. Tactile allodynia, mechanical hyperalgesia and spatial memory were, respectively, evaluated by von Frey, Randall & Selitto and Y-maze tests and molecular events by Western blot analysis. Spinal nerve-ligated animals displayed nociception and impaired spatial memory. Dextromethorphan, but not memantine, reversed neuropathic pain (NP) symptoms, restored spatial memory integrity and decreased the expression of pTyr(1336)NR2B. Following postoperative administration of dextromethorphan, this study has demonstrated for the first time a concordance between behaviour, cognitive function and molecular events via pTyr(1336)NR2B for neuropathic pain alleviation. Confirmation of these findings in patients would constitute a major step forward in the treatment of neuropathic pain and in the improvement of cognitive function and quality of life.
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Affiliation(s)
- Véronique Morel
- Facultés de Médecine/Pharmacie, Laboratoire de Pharmacologie, Clermont Université, Université d'Auvergne, Pharmacologie Fondamentale et Clinique de la Douleur, F-63000, Clermont-Ferrand, France; Inserm, U1107 Neuro-Dol, F-63001, Clermont-Ferrand, France; Centre de Pharmacologie Clinique, CHU Clermont-Ferrand, Inserm CIC 501, F-63003, Clermont-Ferrand, France
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Boulton AJM, Kempler P, Ametov A, Ziegler D. Whither pathogenetic treatments for diabetic polyneuropathy? Diabetes Metab Res Rev 2013; 29:327-33. [PMID: 23381942 DOI: 10.1002/dmrr.2397] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Revised: 01/07/2013] [Accepted: 01/27/2013] [Indexed: 01/17/2023]
Abstract
Diabetic distal symmetric polyneuropathy (DSPN) occurs in around one-third of patients with diabetes and is associated with significant morbidity and increased mortality. Diagnosis and clinical assessment of DSPN remain a challenge, not only for the physician in clinical practice but also for clinical trials. Optimal diabetes control is generally considered an essential first step in the prevention and management of DSPN. However, glycaemic control alone may be insufficient to prevent the development or progression of DSPN, especially in type 2 diabetes. Near-normoglycaemia is also difficult to achieve in a significant proportion of patients. Although considerable advances have been made in symptomatic pain management, these have not addressed the problem of sensory deficits and have no impact on the underlying pathogenesis of DSPN. There remains a lack of treatment options that effectively target the natural history of the disease. Several pathogenetic treatment approaches have been investigated, but evidence from clinical trials is limited with a number of treatments having shown disappointing results. However, some pathogenetic therapies have shown clinically relevant improvements in neuropathic endpoints in randomised controlled trials, in particular α-lipoic acid and Actovegin. These advances in DSPN disease modification need to be confirmed with further robust evidence from clinical trials together with a better understanding of the mechanisms of action of promising treatments.
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Affiliation(s)
- Andrew J M Boulton
- Centre for Endocrinology and Diabetes, University of Manchester, Manchester, UK.
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Ney JP, Devine EB, Watanabe JH, Sullivan SD. Comparative Efficacy of Oral Pharmaceuticals for the Treatment of Chronic Peripheral Neuropathic Pain: Meta-Analysis and Indirect Treatment Comparisons. PAIN MEDICINE 2013; 14:706-19. [DOI: 10.1111/pme.12091] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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Chaparro LE, Wiffen PJ, Moore RA, Gilron I. Combination pharmacotherapy for the treatment of neuropathic pain in adults. Cochrane Database Syst Rev 2012; 2012:CD008943. [PMID: 22786518 PMCID: PMC6481651 DOI: 10.1002/14651858.cd008943.pub2] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND Pharmacotherapy remains an important modality for the treatment of neuropathic pain. However, as monotherapy current drugs are associated with limited efficacy and dose-related side effects. Combining two or more different drugs may improve analgesic efficacy and, in some situations, reduce overall side effects (e.g. if synergistic interactions allow for dose reductions of combined drugs). OBJECTIVES This review evaluated the efficacy, tolerability and safety of various drug combinations for the treatment of neuropathic pain. SEARCH METHODS We identified randomised controlled trials (RCTs) of various drug combinations for neuropathic pain from CENTRAL, MEDLINE, EMBASE and handsearches of other reviews and trial registries. The most recent search was performed on 9 April 2012. SELECTION CRITERIA Double-blind, randomised studies comparing combinations of two or more drugs (systemic or topical) to placebo and/or at least one other comparator for the treatment of neuropathic pain. DATA COLLECTION AND ANALYSIS Data extracted from each study included: proportion of participants a) reporting ≥ 30% pain reduction from baseline OR ≥ moderate pain relief OR ≥ moderate global improvement; b) dropping out of the trial due to treatment-emergent adverse effects; c) reporting each specific adverse effect (e.g. sedation, dizziness) of ≥ moderate severity. The primary comparison of interest was between study drug(s) and one or both single-agent comparators. We combined studies if they evaluated the same drug class combination at roughly similar doses and durations of treatment. We used RevMan 5 to analyse data for binary outcomes. MAIN RESULTS We identified 21 eligible studies: four (578 participants) evaluated the combination of an opioid with gabapentin or pregabalin; two (77 participants) evaluated an opioid with a tricyclic antidepressant; one (56 participants) of gabapentin and nortriptyline; one (120 participants) of gabapentin and alpha-lipoic acid, three (90 participants) of fluphenazine with a tricyclic antidepressant; three (90 participants) of an N-methyl-D-aspartate (NMDA) blocker with an agent from a different drug class; five (604 participants) of various topical medications; one (313 participants) of tramadol with acetaminophen; and another one (44 participants) of a cholecystokinin blocker (L-365,260) with morphine. The majority of combinations evaluated to date involve drugs, each of which share some element of central nervous system (CNS) depression (e.g. sedation, cognitive dysfunction). This aspect of side effect overlap between the combined agents was often reflected in similar or higher dropout rates for the combination and may thus substantially limit the utility of such drug combinations. Meta-analysis was possible for only one comparison of only one combination, i.e. gabapentin + opioid versus gabapentin alone. This meta-analysis involving 386 participants from two studies demonstrated modest, yet statistically significant, superiority of a gabapentin + opioid combination over gabapentin alone. However, this combination also produced significantly more frequent side effect-related trial dropouts compared to gabapentin alone. AUTHORS' CONCLUSIONS Multiple, good-quality studies demonstrate superior efficacy of two-drug combinations. However, the number of available studies for any one specific combination, as well as other study factors (e.g. limited trial size and duration), preclude the recommendation of any one specific drug combination for neuropathic pain. Demonstration of combination benefits by several studies together with reports of widespread clinical polypharmacy for neuropathic pain surely provide a rationale for additional future rigorous evaluations. In order to properly identify specific drug combinations which provide superior efficacy and/or safety, we recommend that future neuropathic pain studies of two-drug combinations include comparisons with placebo and both single-agent components. Given the apparent adverse impact of combining agents with similar adverse effect profiles (e.g. CNS depression), the anticipated development and availability of non-sedating neuropathic pain agents could lead to the identification of more favourable analgesic drug combinations in which side effects are not compounded.
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