Capsaicin 8% Patch Versus Oral Neuropathic Pain Medications for the Treatment of Painful Diabetic Peripheral Neuropathy: A Systematic Literature Review and Network Meta-analysis

Topical treatment of chemotherapy-induced peripheral neuropathy (CIPN) with high-concentration (179 mg) capsaicin patch in breast cancer patients - results of the QUCIP study

Background

Chemotherapy-induced peripheral neuropathy (CIPN) following oral or intravenous chemotherapy often results in neuropathic pain, accompanied by symptoms such tingling, burning and hypersensitivity to stimuli, with a notable decline in quality of life (QoL). Effective therapies for CIPN are lacking, with a high demand for analgesics to address this issue. The QUCIP study aimed to assess the effectiveness of high concentration (179 mg) capsaicin patch (HCCP) in alleviating neuropathic pain and associated symptoms in breast cancer patients with confirmed CIPN.

Methods

QUCIP is a prospective, multi-center observational study spanning 36 weeks with up to three HCCP treatments. Initial treatment (visit V0) was followed by two telephone contacts (T1, T2) and subsequent face-to-face visits every 12 weeks or upon retreatment (visits V1-V3). 73 female patients with painful CIPN post neoadjuvant/adjuvant breast cancer therapy were enrolled. Primary endpoint was the reduction of neuropathic pain symptom score (painDETECT®). Secondary endpoints included improvements in CIPN-specific QoL (QLQ-CIPN20), reductions in pain intensity (numeric pain rating scale, NPRS), and achievement of ≥ 30% and ≥ 50% pain reduction.

Results

Median age was 61 years, with 52.0% of patients experiencing peripheral neuropathic pain for > 1 year (> 2 years: 34.2%). The painDETECT® score significantly decreased from baseline (19.71 ± 4.69) to 15.80 ± 6.20 after initial treatment (p < 0.0001) and continued to decrease at follow-up visits. The NPRS indicated significant pain intensity reduction at each time point, particularly pronounced in patients receiving three HCCP treatments. Clinically significant pain relief of ≥ 30% increased from 25.0% at week 4 (T2) to 36.2%, 43.5%, and 40.0% at weeks 12 (V1), 24 (V2), and 36 (V3), respectively. The percentage of patients achieving pain relief of ≥ 50% increased from 14.7% at T2 to 15.5%, 21.7% and 32.5% at V1, V2 and V3, respectively. Patients further reported a significant improvement in their CIPN-related QoL throughout the study. Adverse drug reactions (ADRs) mainly included application site reactions.

Conclusion

In this study, HCCP shows benefit in managing CIPN in real-world settings. The data demonstrate a sustained and progressive reduction in neuropathic pain and symptomatology, confirming the clinical benefit of repeated treatment observed in former clinical trials. HCCP treatment has also the potential to significantly improve the QoL associated with CIPN. The safety profile of HCCP was confirmed, supporting its use in clinical practice.

Efficacy and safety of topical capsaicin in the treatment of osteoarthritis pain: A systematic review and meta-analysis

Osteoarthritis (OA) affects hundreds of millions of people worldwide. The objective was to critically appraise the efficacy and safety of topical capsaicin in reducing pain in OA. MEDLINE (PubMed) and Embase (Ebsco) were searched from inceptions until February 2023. The eligibility criteria included randomized controlled trials (RCTs), evaluating topical capsaicin in OA patients. Standard Cochrane methods were used to extract data and to appraise eligible studies. Eight double-blind RCTs involving 498 patients were included. Five trials (62.5%) were at an overall low risk of bias, and three (37.5%) were at a high risk of bias. Meta-analysis showed that, in various OA patients, compared with placebo, topical capsaicin (0.0125%-5%) may reduce pain severity measured with visual analog scale (standardized mean difference = -0.84, 95% confidence intervals [CIs] = -1.48 to -0.19, p = 0.01; eight studies). However, topical capsaicin may increase burning sensation at the application site (risk ratio = 5.56, 95% CI = 1.75-17.69, p = 0.004, numbers needed to harm = 3; five studies) when compared with placebo. Limitations include short study durations, small sample sizes, high heterogeneity, and overall low-to-very-low certainty of the evidence. Topical capsaicin may reduce OA pain at follow-ups of up to 3 months. Larger trials, potentially evaluating capsaicin in combination with phytopharmaceuticals having anti-inflammatory effects, with longer follow-ups might be needed to reduce the existing uncertainties. Topical capsaicin might be recommended for short-term management of pain in OA patients intolerant to nonsteroidal anti-inflammatory drugs.

Treating neuropathic pain and comorbid affective disorders: Preclinical and clinical evidence

INTRODUCTION

Neuropathic pain (NP) significantly impacts quality of life and often coexists with affective disorders such as anxiety and depression. Addressing both NP and its psychiatric manifestations requires a comprehensive understanding of therapeutic options. This study aimed to review the main pharmacological and non-pharmacological treatments for NP and comorbid affective disorders to describe their mechanisms of action and how they are commonly used in clinical practice.

METHODS

A review was conducted across five electronic databases, focusing on pharmacological and non-pharmacological treatments for NP and its associated affective disorders. The following combination of MeSH and title/abstract keywords were used: "neuropathic pain," "affective disorders," "depression," "anxiety," "treatment," and "therapy." Both animal and human studies were included to discuss the underlying therapeutic mechanisms of these interventions.

RESULTS

Pharmacological interventions, including antidepressants, anticonvulsants, and opioids, modulate neural synaptic transmission to alleviate NP. Topical agents, such as capsaicin, lidocaine patches, and botulinum toxin A, offer localized relief by desensitizing pain pathways. Some of these drugs, especially antidepressants, also treat comorbid affective disorders. Non-pharmacological techniques, including repetitive transcranial magnetic stimulation, transcranial direct current stimulation, and photobiomodulation therapy, modulate cortical activity and have shown promise for NP and mood disorders.

CONCLUSIONS

The interconnection between NP and comorbid affective disorders necessitates holistic therapeutic strategies. Some pharmacological treatments can be used for both conditions, and non-pharmacological interventions have emerged as promising complementary approaches. Future research should explore novel molecular pathways to enhance treatment options for these interrelated conditions.

Is the Capsaicin 179 mg (8% w/w) Cutaneous Patch an Appropriate Treatment Option for Older Patients with Peripheral Neuropathic Pain?

Introduction

Capsaicin 179 mg (8% weight per weight) cutaneous patch ("capsaicin patch") is a recommended topical treatment for peripheral neuropathic pain (PNP). In older patients, topical treatments may be preferred over systemic treatments, but data specific to the older population are scarce.

Methods

We conducted pooled analyses of multiple clinical trials to evaluate efficacy and safety of capsaicin patch in older patients. The analysis of efficacy included four randomized, double-blind, 12-week studies with similar trial design comparing a single treatment of capsaicin 179 mg cutaneous patch vs low-dose control patch in post-herpetic neuralgia. For the safety evaluation, data were pooled from 18 interventional studies in which capsaicin patch was used in PNP with varying etiologies.

Results

Capsaicin patch had similar analgesic efficacy in elderly (n=582) and non-elderly patients (n=545) in terms of change from baseline to 2-12 weeks in the 11-point numeric pain rating scale (NPRS) score for average pain over the previous 24 hours. In both age groups, decrease in NPRS score was significantly greater with capsaicin patch vs control. Older patients treated with capsaicin patch were significantly more likely than those in the control group to achieve responder status (ie mean decrease in NPRS score from baseline to week 2-12 of at least 30% or ≥2 points): 36.1% vs 27.1% (odds ratio [OR] [95% CI] 1.52 [1.06, 2.18]; P=0.0231) and 33.1% vs 20.9% (OR [95% CI] 1.90 [1.30, 2.78]; P=0.0009) for active treatment vs control group, respectively. Similar proportions of non-elderly patients (n=2,311) and elderly patients (n=537) treated with capsaicin patch experienced treatment-emergent adverse events (TEAEs) (81.6% and 78.1%, respectively) and serious TEAEs (8.2% and 7.2%), with application-site reactions the most common TEAEs in both groups.

Conclusion

The capsaicin patch was equally efficacious and well tolerated in older patients as in younger patients.

Clinical insights into traumatic injury of the inferior alveolar and lingual nerves: a comprehensive approach from diagnosis to therapeutic interventions

OBJECTIVES

This scoping review explores the risk and management of traumatic injuries to the inferior alveolar and lingual nerves during mandibular dental procedures. Emphasizing the significance of diagnostic tools, the review amalgamates existing knowledge to offer a comprehensive overview.

MATERIALS AND METHODS

A literature search across PubMed, Embase, and Cochrane Library informed the analysis.

RESULTS

Traumatic injuries often lead to hypo-/anesthesia and neuropathic pain, impacting individuals psychologically and socially. Diagnosis involves thorough anamnesis, clinical-neurological evaluations, and radiographic imaging. Severity varies, allowing for conservative or surgical interventions. Immediate action is recommended for reversible causes, while surgical therapies like decompression, readaptation, or reconstruction yield favorable outcomes. Conservative management, utilizing topical anesthesia, capsaicin, and systemic medications (tricyclic antidepressants, antipsychotics, and serotonin-norepinephrine-reuptake-inhibitors), proves effective for neuropathic pain.

CONCLUSIONS

Traumatic nerve injuries, though common in dental surgery, often go unrecorded. Despite lacking a definitive diagnostic gold standard, a meticulous examination of the injury and subsequent impairments is crucial.

CLINICAL RELEVANCE

Tailoring treatment to each case's characteristics is essential, recognizing the absence of a universal solution. This approach aims to optimize outcomes, restore functionality, and improve the quality of life for affected individuals.

Update on Treating Painful Diabetic Peripheral Neuropathy: A Review of Current US Guidelines with a Focus on the Most Recently Approved Management Options

Painful diabetic peripheral neuropathy (DPN) is a highly prevalent and disabling complication of diabetes that is often misdiagnosed and undertreated. The management of painful DPN involves treating its underlying cause via lifestyle modifications and intensive glucose control, targeting its pathogenesis, and providing symptomatic pain relief, thereby improving patient function and health-related quality of life. Four pharmacologic options are currently approved by the US Food and Drug Administration (FDA) to treat painful DPN. These include three oral medications (duloxetine, pregabalin, and tapentadol extended release) and one topical agent (capsaicin 8% topical system). More recently, the FDA approved several spinal cord stimulation (SCS) devices to treat refractory painful DPN. Although not FDA-approved specifically to treat painful DPN, tricyclic antidepressants, serotonin/norepinephrine reuptake inhibitors, gabapentinoids, and sodium channel blockers are common first-line oral options in clinical practice. Other strategies may be used as part of individualized comprehensive pain management plans. This article provides an overview of the most recent US guidelines for managing painful DPN, with a focus on the two most recently approved treatment options (SCS and capsaicin 8% topical system), as well as evidence for using FDA-approved and guideline-supported drugs and devices. Also discussed are unmet needs for this patient population, and evidence for potential future treatments for painful DPN, including drugs with novel mechanisms of action, electrical stimulation devices, and nutraceuticals.

Diabetic Neuropathy: An Overview of Molecular Pathways and Protective Mechanisms of Phytobioactives

Diabetic neuropathy (DN) is a common and debilitating complication of diabetes mellitus that affects the peripheral nerves and causes pain, numbness, and impaired function. The pathogenesis of DN involves multiple molecular mechanisms, such as oxidative stress, inflammation, and pathways of advanced glycation end products, polyol, hexosamine, and protein kinase C. Phytochemicals are natural compounds derived from plants that have various biological activities and therapeutic potential. Flavonoids, terpenes, alkaloids, stilbenes, and tannins are some of the phytochemicals that have been identified as having protective potential for diabetic neuropathy. These compounds can modulate various cellular pathways involved in the development and progression of neuropathy, including reducing oxidative stress and inflammation and promoting nerve growth and repair. In this review, the current evidence on the effects of phytochemicals on DN by focusing on five major classes, flavonoids, terpenes, alkaloids, stilbenes, and tannins, are summarized. This compilation also discusses the possible molecular targets of numerous pathways of DN that these phytochemicals modulate. These phytochemicals may offer a promising alternative or complementary approach to conventional drugs for DN management by modulating multiple pathological pathways and restoring nerve function.

Conventional management and current guidelines for painful diabetic neuropathy

Painful Diabetic Peripheral Neuropathy (PDN) is common, affecting around a quarter of patients with both type 1 and type 2 diabetes, and can lead to significant curtailment of functionality and quality of life. Patients may present with unremitting burning, aching or "electric-shock" type pains in their feet, legs and later, in the hands. Conventional management approaches must focus not only on pain relief, but also on concurrent sleep problems, mood disorders and functionality. The mainstay of treatment is pharmacotherapy. Most current international guidelines recommend a choice of four drugs: amitriptyline, duloxetine, pregabalin or gabapentin, as initial treatment for PDN. Recent evidence from the OPTION-DM trial demonstrated that these drugs and their combinations have equivalent efficacy. Moreover, combination treatment provided significant pain relief to patients with inadequate response to the maximum tolerated dose of monotherapy. PDN refractory to pharmacotherapy can be treated with capsaicin 8% or high frequency spinal cord stimulation.

Painful diabetic peripheral neuropathy of the feet: integrating prescription-strength capsaicin into office procedures

Prescription-strength (8%) capsaicin topical system is a US FDA-approved treatment for painful diabetic peripheral neuropathy of the feet. A 30 min application of the capsaicin 8% topical system can provide sustained (up to 3 months) local pain relief by desensitizing and reducing TRPV1-expressing cutaneous fibers. Capsaicin is not absorbed systemically; despite associated application-site discomfort, capsaicin 8% topical system is well tolerated, with no known drug interactions or contraindications, and could offer clinical advantages over oral options. Capsaicin 8% topical system are not for patient self-administration and require incorporation into office procedures, with the added benefit of treatment compliance. This article reviews existing literature and provides comprehensive, practical information regarding the integration of capsaicin 8% topical systems into office procedures.

A Brief Review on the Novel Therapies for Painful Diabetic Neuropathy

PURPOSE OF REVIEW

Almost half of people diagnosed with diabetes mellitus will develop painful diabetic neuropathy (PDN), a condition greatly impacting quality of life with complicated pathology. While there are different FDA approved forms of treatment, many of the existing options are difficult to manage with comorbities and are associated with unwanted side effects. Here, we summarize the current and novel treatments for PDN.

RECENT FINDINGS

Current research is exploring alternative pain management treatments from the first line options of pregabalin, gabapentin, duloxetine, and amitriptyline which often have side effects. The use of FDA approved capsaicin and spinal cord stimulators (SCS) has been incredibly beneficial in addressing this. In addition, new treatments looking at different targets, such as NMDA receptor and the endocannabinoid system, show promising results. There are several treatment options that have been shown to be successful in helping treat PDN, but often require adjunct treatment or alterations due to side effects. While there is ample research for standard medications, treatments such as palmitoylethanolamide and endocannabinoid targets have extremely limited clinical trials. We also found that many studies did not evaluate additional variables other than pain relief, such as functional changes nor were there consistent measurement methods. Future research should continue trials comparing treatment efficacies along with more quality of life measures.

Efficacy of Pregabalin and Duloxetine in Patients with Painful Diabetic Peripheral Neuropathy (PDPN): A Multi-Centre Phase IV Clinical Trial-BLOSSOM

INTRODUCTION

Our trial (ClinicalTrials.gov Identifier: NCT04246619) evaluates the efficacy of two generic medications, pregabalin and duloxetine, for treating pain in PDPN patients.

METHODS

The patients were randomised either into the pregabalin (99) or the duloxetine (102) arm. Pain was evaluated using the DN-4 questionnaire, and visual analogue scales (VASs, 0-100 mm) were used to measure the average pain intensity (API), worst pain intensity (WPI) in the last 24 h and current pain intensity (CPI).

RESULTS

The proportion of patients with a clinically significant improvement in the API at Week 12 was 88.3% [CI 81.7%, 94.8%] in the pregabalin arm and 86.9% [CI 76.7%, 97.1%] in the duloxetine arm. After 12 weeks, the CPI, API, and WPI decreased by -35.3 [-40.5, -30.0], -37.0 [-41.4, -32.6], and -41.6 [-46.6, -36.5] in the pregabalin arm, and by -35.0 [-39.2, -30.7], -36.9 [-41.5, -32.3], and -40.0 [-44.8, -35.2] in the duloxetine arm (all in mm, all p < 0.001).

CONCLUSION

Our results demonstrate that pregabalin and duloxetine are effective medications for treating pain in PDPN in more than 86% of all randomised patients.

Painful Diabetic Peripheral Neuropathy - A Survey of Patient Experiences

Purpose

An online survey was conducted in the USA to obtain information about the knowledge and experiences of patients with painful diabetic peripheral neuropathy (pDPN).

Patients and Methods

506 adults with diabetes and pDPN affecting the feet for ≥6 months, for which pain medication had been prescribed for ≥6 months, completed an online survey questionnaire in March 2021.

Results

79% of respondents had type 2 diabetes, 60% were male, 82% were Caucasian and 87% had comorbidities. Pain was significant to severe in 49% of respondents, and 66% had disability due to nerve pain. Anticonvulsants, over-the-counter pills and supplements were the most commonly used medications. Topical creams/patches were prescribed in 23% of respondents. 70% had tried multiple medications for their pain. 61% of respondents had to see ≥2 doctors before receiving a correct diagnosis of pDPN. 85% of respondents felt that the doctor understood their pain and its impact on their life. 70% had no difficulty finding the information they wanted. 34% felt insufficiently informed about their condition. A medical professional was the primary, and most trusted, source of information. Frustration, worry, anxiety and uncertainty were the most commonly reported emotions. Respondents were generally eager to find new medications for pain relief and desperate for a cure. Lifestyle changes because of nerve pain were most commonly associated with physical disabilities and sleep disturbance. Better treatments and freedom from pain were the overriding perspectives when considering the future.

Conclusion

Patients with pDPN are generally well informed about their pain and trust their doctor but remain unsatisfied with their current treatment and struggle to find a lasting solution for their pain. Early identification and diagnosis of pain in diabetics, and education about treatments, is important to minimize the impact of pain on quality of life and emotional well-being.

Issues and challenges in diabetic neuropathy management: A narrative review

Diabetic neuropathy (DN) is a devastating disorder with an increasing prevalence globally. This epidemic can pose a critical burden on individuals and com-munities, subsequently affecting the productivity and economic output of a country. With more people living a sedentary lifestyle, the incidence of DN is escalating worldwide. Many researchers have relentlessly worked on ways to combat this devastating disease. Their efforts have given rise to a number of commercially available therapies that can alleviate the symptoms of DN. Unfortunately, most of these therapies are only partially effective. Worse still, some are associated with unfavorable side effects. This narrative review aims to highlight current issues and challenges in the management of DN, especially from the perspective of molecular mechanisms that lead to its progression, with the hope of providing future direction in the management of DN. To improve the approaches to diabetic management, the suggested resolutions in the literature are also discussed in this review. This review will provide an in-depth understanding of the causative mechanisms of DN, apart from the insights to improve the quality and strategic approaches to DN management.

A Review of Recent Pharmacological Advances in the Management of Diabetes-Associated Peripheral Neuropathy

Diabetic peripheral neuropathy is a common complication of longstanding diabetes mellitus. These neuropathies can present in various forms, and with the increasing prevalence of diabetes mellitus, a subsequent increase in peripheral neuropathy cases has been noted. Peripheral neuropathy has a significant societal and economic burden, with patients requiring concomitant medication and often experiencing a decline in their quality of life. There is currently a wide variety of pharmacological interventions, including serotonin norepinephrine reuptake inhibitors, gapentanoids, sodium channel blockers, and tricyclic antidepressants. These medications will be discussed, as well as their respective efficacies. Recent advances in the treatment of diabetes mellitus with incretin system-modulating drugs, specifically glucagon-like peptide-1 agonists, have been promising, and their potential implication in the treatment of peripheral diabetic neuropathy is discussed in this review.

Recent Progress in Gels for Neuropathic Pain

Neuropathic pain is a complex and debilitating condition that affects millions of people worldwide. While several treatment options are available, they often have limited efficacy and are associated with adverse effects. In recent years, gels have emerged as a promising option for the treatment of neuropathic pain. Inclusion of various nanocarriers, such as cubosomes and niosomes, into gels results in pharmaceutical forms with higher drug stability and increased drug penetration into tissues compared to products currently marketed for the treatment of neuropathic pain. Furthermore, these compounds usually provide sustained drug release and are biocompatible and biodegradable, which makes them a safe option for drug delivery. The purpose of this narrative review was to provide a comprehensive analysis of the current state of the field and identify potential directions for future research in the development of effective and safe gels for the treatment of neuropathic pain, ultimately improving the quality of life for patients suffering from neuropathic pain.

Efficacy and safety of duloxetine in painful diabetic peripheral neuropathy: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Painful diabetic peripheral neuropathy (PDPN) is a key concern in clinical practice. In this systematic review and meta-analysis, we compared duloxetine and placebo treatments in terms of their efficacy and safety in patients with PDPN.

METHODS

Following the PRISMA guidelines, we searched the Cochrane Library, PubMed, and Embase databases for relevant English articles published before January 11, 2021. Treatment efficacy and safety were assessed in terms of pain improvement, patient-reported health-related performance, and patients' quality of life.

RESULTS

We reviewed a total of 7 randomized controlled trials. Regarding pain improvement, duloxetine was more efficacious than placebo (mean difference [MD] - 0.89; 95% confidence interval [CI] - 1.09 to - 0.69; P < .00001). Furthermore, duloxetine significantly improved the patients' quality of life, which was assessed using the Clinical Global Impression severity subscale (MD - 0.48; 95% CI - 0.61 to - 0.36; P < .00001), Patient Global Impression of Improvement scale (MD - 0.50; 95% CI - 0.64 to - 0.37; P < .00001), and European Quality of Life Instrument 5D version (MD 0.04; 95% CI 0.02 to 0.07; P = .0002). Severe adverse events were rare, whereas nausea, somnolence, dizziness, fatigue, constipation, and decreased appetite were common; approximately, 12.6% of all patients dropped out because of the common symptoms.

CONCLUSIONS

Duloxetine is more efficacious than placebo treatments in patients with PDPN. The rarity of severe adverse events indicates that duloxetine is safe. When a 60-mg dose is insufficient, 120 mg of duloxetine may improve PDPN symptoms. Our findings may help devise optimal treatment strategies for PDPN.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021225451.

[Diabetic neuropathy and diabetic foot syndrome (update 2023)]

These are the guidelines for diagnosis and treatment of diabetic neuropathy and diabetic foot.The position statement summarizes characteristic clinical symptoms and techniques for diagnostic assessment of diabetic neuropathy, including the complex situation of the diabetic foot syndrome. Recommendations for the therapeutic management of diabetic neuropathy, especially for the control of pain in sensorimotor neuropathy, are provided. The needs to prevent and treat diabetic foot syndrome are summarized.

[Post-traumatic pain mononeuropathies]

Neuropathic pain syndrome (NPS) caused by peripheral nerve (PN) injury is a serious clinical problem due to its prevalence, complexity of pathogenesis, significant impact on the quality of life of patients. The issues of epidemiology, pathogenesis and treatment of patients with NBS with PN injury are considered. Modern possibilities of invasive treatment of such patients are discussed.

Prevention and Management Strategies for Diabetic Neuropathy

Diabetic neuropathy (DN) is a common complication of diabetes that is becoming an increasing concern as the prevalence of diabetes rapidly rises. There are several types of DN, but the most prevalent and studied type is distal symmetrical polyneuropathy, which is the focus of this review and is simply referred to as DN. It can lead to a wide range of sensorimotor and psychosocial symptoms and is a major risk factor for diabetic foot ulceration and Charcot neuropathic osteoarthropathy, which are associated with high rates of lower limb amputation and mortality. The prevention and management of DN are thus critical, and clinical guidelines recommend several strategies for these based on the best available evidence. This article aims to provide a narrative review of DN prevention and management strategies by discussing these guidelines and the evidence that supports them. First, the epidemiology and diverse clinical manifestations of DN are summarized. Then, prevention strategies such as glycemic control, lifestyle modifications and footcare are discussed, as well as the importance of early diagnosis. Finally, neuropathic pain management strategies and promising novel therapies under investigation such as neuromodulation devices and nutraceuticals are reviewed.

Targeting TRPV1 activity via high-dose capsaicin in patients with sickle cell disease

Evidence suggests neuropathic pain (NP) develops over time in sickle cell disease (SCD), contributing to a complex, difficult-to-treat phenotype, with management based on scant evidence. One characteristic of NP found is hyperalgesia caused by nervous system sensitization, but risk factors for this have not been identified within the SCD population, as exact mechanisms leading to its development are not well defined. The SPICE (Sickle cell Pain: Intervention with Capsaicin Exposure) trial was a pilot safety and feasibility trial of high-dose (8%) topical capsaicin for patients with SCD and recurrent/chronic pain with neuropathic features, aimed at exploring capsaicin's utility as a mechanistic probe and adjunctive pain treatment for this population. Ten participants identifying "target" sites of pain with NP-type qualities consented to treatment. The primary endpoint was safety/tolerability. The novel Localized Peripheral Hypersensitivity Relief score (LPHR) was developed to determine improvement in sensitivity attributable to TRPV1 neutralization. There were no severe treatment-related adverse events. Higher baseline pain sensitivity at a given body site was associated with self-reported history of more frequent localized vaso-occlusive pain episodes at that site. There was a statistically significant improvement in the mean LPHR, evidencing TRPV1's importance to the development of hypersensitivity and a potential therapeutic benefit of capsaicin for SCD.

Pathogenesis of Distal Symmetrical Polyneuropathy in Diabetes

Distal symmetrical polyneuropathy (DSPN) is a serious complication of diabetes associated with significant disability and mortality. Although more than 50% of people with diabetes develop DSPN, its pathogenesis is still relatively unknown. This lack of understanding has limited the development of novel disease-modifying therapies and left the reasons for failed therapies uncertain, which is critical given that current management strategies often fail to achieve long-term efficacy. In this article, the pathogenesis of DSPN is reviewed, covering pathogenic changes in the peripheral nervous system, microvasculature and central nervous system (CNS). Furthermore, the successes and limitations of current therapies are discussed, and potential therapeutic targets are proposed. Recent findings on its pathogenesis have called the definition of DSPN into question and transformed the disease model, paving the way for new research prospects.

Evidence-Based Treatment of Painful Diabetic Neuropathy: a Systematic Review

PURPOSE OF REVIEW

Painful diabetic neuropathy (PDN) manifests with pain typically in the distal lower extremities and can be challenging to treat. The authors appraised the literature for evidence on conservative, pharmacological, and neuromodulation treatment options for PDN.

RECENT FINDINGS

Intensive glycemic control with insulin in patients with type 1 diabetes may be associated with lower odds of distal symmetric polyneuropathy compared to patients who receive conventional insulin therapy. First-line pharmacologic therapy for PDN includes gabapentinoids (pregabalin and gabapentin) and duloxetine. Additional pharmacologic modalities that are approved by the Food and Drug Administration (FDA) but are considered second-line agents include tapentadol and 8% capsaicin patch, although studies have revealed modest treatment effects from these modalities. There is level I evidence on the use of dorsal column spinal cord stimulation (SCS) for treatment of PDN, delivering either a 10-kHz waveform or tonic waveform. In summary, this review provides an overview of treatment options for PDN. Furthermore, it provides updates on the level of evidence for SCS therapy in cases of PDN refractory to conventional medical therapy.

Efficacy and safety of Mudan granules for painful diabetic peripheral neuropathy: A protocol for a double-blind randomized controlled trial

BACKGROUND

As one of the most challenging complications in the management of diabetes mellitus, painful diabetic peripheral neuropathy (PDPN) is accompanied by various clinical manifestations, including numbness, burning, coldness, and other sensory abnormalities in the extremities. Meanwhile, PDPN seriously affects the life quality of patients and causes great pain. Western medicine mostly provides symptomatic treatments, such as antioxidants, aldose reductase inhibitors, nerve nutrition, microcirculation improvement, and analgesic drugs on the basis of blood sugar control. Although certain efficacy has been achieved, the problem has not been solved at root. Mudan granules have some advantages in the treatment of PDPN, but there is insufficient high-quality clinical studies to verify this. Therefore, the purpose of this study was to evaluate the efficacy and safety of Mudan granules in treating PDPN.

METHODS

A randomized, double-blind, placebo, and parallel-controlled trial design was used to study the efficacy and safety of Mudan granules in the treatment of PDPN. In this study, 93 patients with painful diabetic neuropathy were recruited and randomly divided into a treatment group and a placebo group based on 1:1. The treatment group was given Mudan granules and the control group accepted placebo treatment, and the basic treatment was performed according to the recommended guidelines. During the treatment period, the patients' visual analog scores, clinical efficacy, Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) scores, nerve conduction velocity, and drug-induced adverse reactions were observed at baseline after 8 and 10 weeks.

DISCUSSION

This study will evaluate the efficacy and safety of Mudan granules in treating PDPN. The experimental results will provide evidence support to treat PDPN with Mudan granules.

TRIAL REGISTRATION

DOI 10.17605/OSF.IO/5CE32.

Current Strategies for the Management of Painful Diabetic Neuropathy

The development of painful diabetic neuropathy (PDN) is a common complication of chronic diabetes that can be associated with significant disability and healthcare costs. Prompt symptom identification and aggressive glycemic control is essential in controlling the development of neuropathic complications; however, adequate pain relief remains challenging and there are considerable unmet needs in this patient population. Although guidelines have been established regarding the pharmacological management of PDN, pain control is inadequate or refractory in a high proportion of patients. Pharmacotherapy with anticonvulsants (pregabalin, gabapentin) and antidepressants (duloxetine) are common first-line agents. The use of oral opioids is associated with considerable morbidity and mortality and can also lead to opioid-induced hyperalgesia. Their use is therefore discouraged. There is an emerging role for neuromodulation treatment modalities including intrathecal drug delivery, spinal cord stimulation, and dorsal root ganglion stimulation. Furthermore, consideration of holistic alternative therapies such as yoga and acupuncture may augment a multidisciplinary treatment approach. This aim of this review is to focus on the current management strategies for the treatment of PDN, with a discussion of treatment rationale and practical considerations for their implementation.

The role of the capsaicin 8% patch in the treatment of painful diabetic peripheral neuropathy

Treatment of painful diabetic peripheral neuropathy (PDPN) is challenging and often limited by drug tolerability and adverse effects. This review article focuses on the high-dose (8%) capsaicin patch that allows for improved efficacy and reduced application frequency in comparison to low-dose capsaicin formulations. Systemic absorption is minimal resulting in fewer systemic side effects than first-line oral medications. There is evidence that capsaicin patch treatment is well-tolerated, safe and provides effective pain relief maintained for several weeks; well-powered studies are needed to confirm these findings. The capsaicin 8% patch may benefit patients at high risk for adverse effects from oral medication, polypharmacy or inadequate pain relief from first-line therapies.

Peripheral Neuropathic Pain Following Breast Cancer: Effectiveness and Tolerability of High-Concentration Capsaicin Patch

Purpose

Data supporting the use of high-concentration capsaicin patches (HCCPs) in breast cancer (BC) patients and BC survivors (BCSs) with peripheral neuropathic pain (PNP) are limited. This observational study evaluated the effectiveness and safety of HCCP applications in BCSs/BC patients with PNP.

Patients and Methods

Data from all patients treated with HCCP in the pain department of a French comprehensive cancer centre were collected from 01-Jan-2014 to 14-Oct-2020. Independent pain specialists completed the Clinical Global Impression of Change (CGIC) for each included patient based on data extracted from patient’s electronic medical record compiled by the treating pain specialist after each HCCP application.

Results

Patients (N=279; mean age: 59.2 years; previous history of PNP medication: 54.5%) received on average 4.1 repeated HCCP applications (1141 HCCP applications); 68.8% received HCCP as an add-on to systemic therapy and 27.9% as first-line therapy. PNP was most frequently caused by surgery (62.4%) followed by chemotherapy (11.8%) and radiotherapy (6.5%). A complete or important analgesic effect was reported at least once by 82.3% of patients. A 6.0% reported no effect at all. For post-surgical PNP existing for <12 months and >10 years an important or complete effect was observed for 70.7% and 56.0% of applications. For chemotherapy- or radiotherapy-induced PNP, this important or complete effect was observed for 52.7% and 52.3% of applications, respectively. HCCP application was associated with site reactions in 54.4% of patients (mainly burning sensation or pain, 45.9%, or erythema, 30.8%) and high blood pressure in 7.2%.

Conclusion

This real-world chart review provides important effectiveness and safety information to clinicians when considering topical options to treat PNP in BCSs/BC patients.

Molecular Mechanism of Gelsemium elegans (Gardner and Champ.) Benth. Against Neuropathic Pain Based on Network Pharmacology and Experimental Evidence

Gelsemium elegans (Gardner and Champ.) Benth. (Gelsemiaceae) (GEB) is a toxic plant indigenous to Southeast Asia especially China, and has long been used as Chinese folk medicine for the treatment of various types of pain, including neuropathic pain (NPP). Nevertheless, limited data are available on the understanding of the interactions between ingredients-targets-pathways. The present study integrated network pharmacology and experimental evidence to decipher molecular mechanisms of GEB against NPP. The candidate ingredients of GEB were collected from the published literature and online databases. Potentially active targets of GEB were predicted using the SwissTargetPrediction database. NPP-associated targets were retrieved from GeneCards, Therapeutic Target database, and DrugBank. Then the protein-protein interaction network was constructed. The DAVID database was applied to Gene Ontology and Kyoto Encyclopedia of Genes and Genome pathway enrichment analysis. Molecular docking was employed to validate the interaction between ingredients and targets. Subsequently, a 50 ns molecular dynamics simulation was performed to analyze the conformational stability of the protein-ligand complex. Furthermore, the potential anti-NPP mechanisms of GEB were evaluated in the rat chronic constriction injury model. A total of 47 alkaloids and 52 core targets were successfully identified for GEB in the treatment of NPP. Functional enrichment analysis showed that GEB was mainly involved in phosphorylation reactions and nitric oxide synthesis processes. It also participated in 73 pathways in the pathogenesis of NPP, including the neuroactive ligand-receptor interaction signaling pathway, calcium signaling pathway, and MAPK signaling pathway. Interestingly, 11-Hydroxyrankinidin well matched the active pockets of crucial targets, such as EGFR, JAK1, and AKT1. The 11-hydroxyrankinidin-EGFR complex was stable throughout the entire molecular dynamics simulation. Besides, the expression of EGFR and JAK1 could be regulated by koumine to achieve the anti-NPP action. These findings revealed the complex network relationship of GEB in the "multi-ingredient, multi-target, multi-pathway" mode, and explained the synergistic regulatory effect of each complex ingredient of GEB based on the holistic view of traditional Chinese medicine. The present study would provide a scientific approach and strategy for further studies of GEB in the treatment of NPP in the future.

Role of Mechanoinsensitive Nociceptors in Painful Diabetic Peripheral Neuropathy

The cutaneous mechanisms that trigger spontaneous neuropathic pain in diabetic peripheral neuropathy (PDPN) are far from clear. Two types of nociceptors are found within the epidermal and dermal skin layers. Small-diameter lightly myelinated Aδ and unmyelinated C cutaneous mechano and heat-sensitive (AMH and CMH) and C mechanoinsensitive (CMi) nociceptors transmit pain from the periphery to central nervous system. AMH and CMH fibers are mainly located in the epidermis, and CMi fibers are distributed in the dermis. In DPN, dying back intra-epidermal AMH and CMH fibers leads to reduced pain sensitivity, and the patients exhibit significantly increased pain thresholds to acute pain when tested using traditional methods. The role of CMi fibers in painful neuropathies has not been fully explored. Microneurography has been the only tool to access CMi fibers and differentiate AMH, CMH, and CMi fiber types. Due to the complexity, its use is impractical in clinical settings. In contrast, a newly developed diode laser fiber selective stimulation (DLss) technique allows to safely and selectively stimulate Aδ and C fibers in the superficial and deep skin layers. DLss data demonstrate that patients with painful DPN have increased Aδ fiber pain thresholds, while C-fiber thresholds are intact because, in these patients, CMi fibers are abnormally spontaneously active. It is also possible to determine the involvement of CMi fibers by measuring the area of DLss-induced neurogenic axon reflex flare. The differences in AMH, CMH, and CMi fibers identify patients with painful and painless neuropathy. In this review, we will discuss the role of CMi fibers in PDPN.

Modulating effects of capsaicin on glucose homeostasis and the underlying mechanism

Abnormal glucose homeostasis is linked to a variety of metabolic syndromes, such as insulin resistance, obesity, type-2 diabetes mellitus, hypertension and cardiovascular diseases. Maintenance of normal glucose homeostasis is important for the body to keep normal biological functions. As the major bioactive ingredient in chili peppers responsible for the pungent flavor, capsaicin has been reported to effectively improve glucose homeostasis with low cytotoxicity. In this review, the modulating effects of capsaicin on glucose homeostasis in cell models, animal models and human trials are summarized through both TRPV1 dependent and TRPV1 independent pathways. The relevant molecular mechanisms underlying its regulatory effects are also evaluated. Understanding the effects and mechanisms of capsaicin on glucose metabolism could provide theoretical evidence for its application in the food and pharmaceutical industries.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Topical Capsaicin for the Treatment of Neuropathic Pain

BACKGROUND

Neuropathic pain (NP) is an egregious problem worldwide. Due to the side-effects of oral drugs, drugs delivered directly to the affected area of pain are preferred.

OBJECTIVE

Capsaicin, a chemical compound isolated from chili peppers, is used as an analgesic in topical ointments and dermal patches to alleviate pain. Objective of the study is to review the application and functionality of topical capsaicin in treatment of neuropathic pain.

DATA SOURCES

To systematically review capsaicin's functions on NP, we retrieved articles from the PubMed database published in the last ten years.

STUDY ELIGIBILITY CRITERIA

The inclusion criteria were capsaicin and the use of capsaicin for the treatment of NP; on the other hand, articles were excluded according to the mentioned criteria such as abstracts, articles written in any language other than English, incomplete articles, and conference papers.

PARTICIPANTS AND INTERVENTIONS

Out of 265 articles, 108 articles were selected after filtering through the inclusion and exclusion criteria. The data and knowledge currently existing for capsaicin treatment in NP are summarized.

RESULTS

This review indicates that capsaicin effectively improves NP treatment without affecting the motor and large nerve fibres involved in sensory function. Transient receptor potential channel vanilloid type 1 (TRPV1) is the capsaicin receptor expressed in central and peripheral terminals of a sensitive primary nerve cell. Conclusions and implications of key findings: Topical capsaicin has a sensible safety profile and is effective in reducing NP. Therefore, studies over the last decade suggest that capsaicin might be a potential drug for NP treatment.

Progressive Response to Repeat Application of Capsaicin 179 mg (8% w/w) Cutaneous Patch in Peripheral Neuropathic Pain: Comprehensive New Analysis and Clinical Implications

Objective

To investigate the efficacy of repeated application of capsaicin 179 mg cutaneous patch in nonresponders to the first application.

Design

Post hoc, as-treated analysis of two prospective trials (STRIDE and PACE) with 52-week follow-up.

Blinding

Open-label.

Setting

Multicenter clinical trial.

Subjects

STRIDE: nondiabetic neuropathic pain; PACE: painful diabetic peripheral neuropathy.

Methods

Patients were divided according to number of applications needed before attainment of a ≥30% reduction in average pain intensity (question 5 of the Brief Pain Inventory [BPI-Q5]). We assessed the change from baseline in average pain intensity (BPI-Q5), mean “interference with sleep” score, Patient Global Impression of Change, quality of life (QOL) via the EuroQol 5-dimension, and Self-Assessment of Treatment.

Results

In STRIDE and PACE, respectively, n = 306 and n = 313 received the capsaicin patch; n = 60 and n = 96 had a response after the first application, n = 33 and n = 68 after the second, and n = 11 and n = 43 after the third. Among patients without a ≥30% reduction in pain intensity at 3 months, in STRIDE and PACE, respectively, 23.3% and 28.1% achieved a ≥30% reduction at 6 months, increasing to 33.9% and 45.7% at 12 months. Similar results were obtained when a decrease of ≥50% was used as the responder definition. Progressive improvements in pain intensity in slower responders reached levels similar to those in early responders at month 12 and were accompanied by improvements in sleep, QOL, and patient satisfaction.

Conclusions

Although some patients with peripheral neuropathic pain experience rapid improvements with a single treatment of capsaicin 179 mg patch, some may require two or three treatments before an initial response is observed. Similar benefits for pain, sleep, and QOL can be achieved in early and late responders.

Chemotherapy-induced peripheral neuropathy (CIPN): current therapies and topical treatment option with high-concentration capsaicin

Cancer diagnosis and treatment are drastic events for patients and their families. Besides psychological aspects of the disease, patients are often affected by severe side effects related to the cancer itself or as a result of therapeutic interventions. Particularly, chemotherapy-induced peripheral neuropathy (CIPN) is the most prevalent neurological complication of oral or intravenous chemotherapy. The disorder may require dose reduction of chemotherapy and is accompanied by multiple symptoms with long-term functional impairment affecting quality of life (QoL), e.g., sensory and functional deteriorations as well as severe pain. Although CIPN may reverse or improve after termination of the causative chemotherapy, approximately 30–40% of patients are faced with chronicity of the symptoms. Due to the advantages in cancer diagnosis and treatments, survival rates of cancer patients rise and CIPN may occur even more frequently in the future. In this review, we summarize current recommendations of leading national and international societies regarding prevention and treatment options in CIPN. A special focus will be placed on current evidence for topical treatment of CIPN with high-dose capsaicin. Finally, an algorithm for CIPN treatment in clinical practice is provided, including both pharmacologic and non-pharmacologic modalities based on the clinical presentation.

A critical review of the capsaicin 8% patch for the treatment of neuropathic pain associated with diabetic peripheral neuropathy of the feet in adults

INTRODUCTION

Diabetes is an increasingly prevalent disorder affecting nearly 1-in-5 adults, of which half will experience diabetic peripheral neuropathy (DPN) and a quarter will suffer from diabetic peripheral nerve pain (DPNP), severely impacting quality of life. The currently approved treatment options are typically centrally acting agents whose use is limited by systemic effects and drug interactions. The capsaicin 8% dermal patch was recently approved by the U.S. FDA for the treatment of DPNP.

AREAS COVERED

The authors review the available literature regarding the use of high-concentration capsaicin 8% patch for the treatment of diabetic peripheral neuropathy and neuropathic pain and discuss implementing its use in clinical practice.

EXPERT OPINION

The high-concentration capsaicin 8% patch is an effective and well-tolerated treatment option for treating DPNP. Capsaicin 8% patch may be used alone or in combination with other oral therapies and can provide rapid and sustained neuropathic pain relief following a single application and is safe and effective when used long term.

Injectable Capsaicin for the Management of Pain Due to Osteoarthritis

Capsaicin is a potent agonist of the TRPV1 channel, a transduction channel that is highly expressed in nociceptive fibers (pain fibers) throughout the peripheral nervous system. Given the importance of TRPV1 as one of several transduction channels in nociceptive fibers, much research has been focused on the potential therapeutic benefits of using TRPV1 antagonists for the management of pain. However, an antagonist has two limitations. First, an antagonist in principle generally only affects one receptor. Secondly, most antagonists must have an ongoing presence on the receptor to have an effect. Capsaicin overcomes both liabilities by disrupting peripheral terminals of nociceptive fibers that express TRPV1, and thereby affects all of the potential means of activating that pain fiber (not just TRPV1 function). This disruptive effect is dependent on the dose and can occur within minutes. Thus, unlike a typical receptor antagonist, continued bioavailability at the level of the receptor is not necessary. By disrupting the entire terminal of the TRPV1-expressing nociceptive fiber, capsaicin blocks all the activation mechanisms within that fiber, and not just TRPV1 function. Topical capsaicin, an FDA approved treatment for neuropathic pain, addresses pain from abnormal nociceptor activity in the superficial layers of the skin. Effects after a single administration are evident over a period of weeks to months, but in time are fully reversible. This review focuses on the rationale for using capsaicin by injection for painful conditions such as osteoarthritis (OA) and provides an update on studies completed to date.

Comprehensive Review of Topical Analgesics for Chronic Pain

PURPOSE OF REVIEW

Topical analgesics are a non-opioid option for the treatment of chronic pain conditions including neuropathic pain, musculoskeletal pain, and osteoarthritis. There are many topical medications available; however their efficacy is variable. This article reviews the various topical analgesics, their mechanisms of action, and their efficacy.

RECENT FINDINGS

Studies have found topical NSAIDs are useful in treating acute musculoskeletal pain syndromes (strains and sprains) and show some efficacy in treating hand and knee osteoarthritis (Derry et al. Cochrane Database Syst Rev 5:CD008609, 2017). Topical capsaicin 8% has been shown to be efficacious in the treatment of postherpetic neuralgia, painful diabetic peripheral neuropathy, and HIV-neuropathy (Derry et al. Cochrane Database Syst Rev 1:CD007393, 2017). Topical lidocaine has been widely studied and found to reduce pain in patients with postherpetic neuralgia (Knezevic et al. Pain Manag 7:537-58, 2017). Although many other topical analgesics are available, there is limited data to support the efficacy of other agents. Topical analgesics are a relatively benign treatment for chronic pain conditions including neuropathic pain, musculoskeletal, and myofascial pain. There is evidence to support the use of topical NSAIDs, high concentration topical capsaicin, and topical lidocaine for various painful conditions.

The efficacy and safety profile of capsaicin 8% patch versus 5% Lidocaine patch in patients with diabetic peripheral neuropathic pain: a randomized, placebo-controlled study of south Asian male patients

Aims

Diabetic peripheral neuropathy affects up to 60% of individuals and often leads to foot ulceration and eventual amputation. When oral therapy has failed to achieve pain relief, the first line local treatment is the 5% lidocaine-medicated plaster which provides local relief. Capsaicin 8% patch is considered a promising topical treatment for diabetic peripheral neuropathy. The present study investigated the efficacy, safety and tolerability of capsaicin 8% patch vs 5% lidocaine patch treatments over 24 weeks in South Asian male diabetic patients with established peripheral diabetic neuropathy.

Methods

Analgesic effectiveness was assessed by observing any change in the Numeric Pain Rating Scale (NPRS) score, Brief Pain Inventory (BPI) for painful diabetic peripheral neuropathy (BPI-DPN question 4) and Patient Global Impression of Change (PGIC). All patients received 4% lidocaine gel/cream for 60 min prior to patch application. The trial was probably underpowered, taking into account the smaller than expected number of participants from the calculated 350 sample size required for the whole study. Two hundred ninety-one individuals were divided into three groups based on treatment regimen; Group LL (Lidocaine + Lidocaine), Group LP (Lidocaine + Placebo), Group LC (Lidocaine + Capsaicin). The treatment procedure was conducted once initially and then repeated once at 12 weeks. The patients were followed up on alternate weeks till 24 weeks after the initial treatment.

Results

Group LC experienced a more significant reduction in the average pain intensity (p < 0.05) during the last twenty-four hours. Group LC showed more significant reduction of pain compared to control (p < 0.01), a baseline score of 5.4 ± 1.2 dropped to 3.2 ± 1.5 by week 24 of treatment. The change in mean daily pain intensity was - 2.2 ± 1.5 [95% CI: -2.45, -1.5]. Group LL and LC experienced a significant overall improvement (slightly, much or very much) in the health status during the study. After the second week of the treatment, patient satisfaction scores were 2.1 ± 1.1 in Group LL which increased to 3.2 ± 1.2 by week 24 of treatment. The capsaicin 8% patch appears to be reasonably well tolerated since there were no discontinuations because of serious drug-related treatment emergent adverse event (TEAEs).

Conclusions

The aim of the present study was to assess the efficacy, safety and tolerability of the 8% capsaicin patch in patients with established painful diabetic neuropathy. There was a sustained treatment response to the initial and repeat treatment of the capsaicin 8% patch over the 24 weeks. The study population was very specific so further studies are required to investigate the generalizability of the results for patients experiencing painful diabetic neuropathy. The patch could be considered as an effective long-term treatment option in individuals with painful diabetic neuropathy, particularly those experiencing inadequate pain relief or side effects from systemic therapies.

Oral or Topical Pain Therapy-How Would Patients Decide? A Discrete Choice Experiment in Patients with Peripheral Neuropathic Pain

To ensure an adequate pain therapy with high patient adherence, it is necessary to know and consider patient preferences. A discrete choice experiment was used to obtain patients' preferences regarding treatment with systemic or topical pain medication. Patients with peripheral neuropathic pain (pNP) were recruited in two pain-focused practices in Germany. To identify relevant attributes of topical or systemic pain medication, a literature review and face-to-face interviews with experts for pain treatment were conducted. The attributes used in the choice scenarios were noticeable onset of effect, time spent in medical office, risk of systemic and local side effects, and impairment of daily life with regard to sleep quality and sexuality. The model was estimated with a mixed multinomial logit regression model. The study included 153 participants suffering from moderate to severe pNP. Most important attributes from patient's perspective was noticeable onset of effect (odds ratio 2.141 [95% confidence interval 1.837 to 2.494]), followed by risk of systemic side effects (2.038 [1.731 to 2.400]) and risk of sexual dysfunction (1.839 [1.580 to 2.140]), while risk of local side effects regarding skin ranked fourth (1.612 [1.321 to 1.966]). The impairment of sleep quality was also significant but less important (1.556 [1.346 to 1.798]). Local side effects were more likely to be accepted than systemic side effects. The risk of sexual dysfunction as a side effect of treatment is very important for patients, although it has received little attention in the literature.

Animal models of pain: Diversity and benefits

Chronic pain is a maladaptive neurological disease that remains a major health problem. A deepening of our knowledge on mechanisms that cause pain is a prerequisite to developing novel treatments. A large variety of animal models of pain has been developed that recapitulate the diverse symptoms of different pain pathologies. These models reproduce different pain phenotypes and remain necessary to examine the multidimensional aspects of pain and understand the cellular and molecular basis underlying pain conditions. In this review, we propose an overview of animal models, from simple organisms to rodents and non-human primates and the specific traits of pain pathologies they model. We present the main behavioral tests for assessing pain and investing the underpinning mechanisms of chronic pathological pain. The validity of animal models is analysed based on their ability to mimic human clinical diseases and to predict treatment outcomes. Refine characterization of pathological phenotypes also requires to consider pain globally using specific procedures dedicated to study emotional comorbidities of pain. We discuss the limitations of pain models when research findings fail to be translated from animal models to human clinics. But we also point to some recent successes in analgesic drug development that highlight strategies for improving the predictive validity of animal models of pain. Finally, we emphasize the importance of using assortments of preclinical pain models to identify pain subtype mechanisms, and to foster the development of better analgesics.

Fight fire with fire: Neurobiology of capsaicin-induced analgesia for chronic pain

Capsaicin, the pungent ingredient in chili peppers, produces intense burning pain in humans. Capsaicin selectively activates the transient receptor potential vanilloid 1 (TRPV1), which is enriched in nociceptive primary afferents, and underpins the mechanism for capsaicin-induced burning pain. Paradoxically, capsaicin has long been used as an analgesic. The development of topical patches and injectable formulations containing capsaicin has led to application in clinical settings to treat chronic pain conditions, such as neuropathic pain and the potential to treat osteoarthritis. More detailed determination of the neurobiological mechanisms of capsaicin-induced analgesia should provide the logical rationale for capsaicin therapy and help to overcome the treatment's limitations, which include individual differences in treatment outcome and procedural discomfort. Low concentrations of capsaicin induce short-term defunctionalization of nociceptor terminals. This phenomenon is reversible within hours and, hence, likely does not account for the clinical benefit. By contrast, high concentrations of capsaicin lead to long-term defunctionalization mediated by the ablation of TRPV1-expressing afferent terminals, resulting in long-lasting analgesia persisting for several months. Recent studies have shown that capsaicin-induced Ca²⁺/calpain-mediated ablation of axonal terminals is necessary to produce long-lasting analgesia in a mouse model of neuropathic pain. In combination with calpain, axonal mitochondrial dysfunction and microtubule disorganization may also contribute to the longer-term effects of capsaicin. The analgesic effects subside over time in association with the regeneration of the ablated afferent terminals. Further determination of the neurobiological mechanisms of capsaicin-induced analgesia should lead to more efficacious non-opioidergic analgesic options with fewer adverse side effects.

Expert Opinion: Exploring the Effectiveness and Tolerability of Capsaicin 179 mg Cutaneous Patch and Pregabalin in the Treatment of Peripheral Neuropathic Pain

Background and Objective

Treatment of peripheral neuropathic pain (PNP) remains a challenge. In the absence of clear predictors of response, clinical decision-making involves trial and error. While many classes of pharmacological agent are used and have shown efficacy, one of the most commonly used first-line treatments is pregabalin. However, in the 60% of PNP cases in which the pain is localized, a local treatment may be more suitable. This article will summarize the evidence for the relative effectiveness and tolerability of the capsaicin 179 mg patch and pregabalin in the treatment of PNP and highlight the expert opinion of the authors based on their own clinical experiences.

Results

When compared in a head-to-head trial in patients with PNP, capsaicin 179 mg patch provided non-inferior pain relief compared with an optimized dose of pregabalin, as well as a reduction in dynamic mechanical allodynia, faster onset of action, fewer systemic side effects, and greater treatment satisfaction. Adverse events associated with capsaicin patch are mainly application site reactions, compared with systemic and central nervous system effects with pregabalin. Studies indicate that capsaicin 179 mg patch is associated with a lower burden of therapy than pregabalin in terms of improved tolerability, lack of a daily pill burden, lack of drug-drug interactions, and increased regimen flexibility.

Conclusion

In localized neuropathic pain, evidence supports a pragmatic approach of using a local treatment before considering a systemic treatment. For treatment selection, the patient profile (eg, concomitant medication use, age) and the treatments' efficacy and tolerability profiles should be considered.

[Pain treatment in old age: special features and recommendations]

BACKGROUND

For geriatric patients with chronic pain, a comprehensive well-coordinated pain management is pivotal to ensure the best possible pain relief and to minimize as far as possible preventable negative side effects of treatment.

OBJECTIVE

Description of the difficulties in pain management of geriatric patients with respect to general basic rules that are worth paying attention to and presentation of pharmacological and non-pharmacological treatment options.

METHODS

This article describes the special features of pain management in older patients and gives recommendations on the use of analgesics and potential drug interactions in geriatric patients with organ dysfunction. Furthermore, individual substance groups are described with respect to their use in geriatric patients based on the recent literature.

CONCLUSION

The aim of an individualized pain treatment in older and multimorbid patients is the relief of pain to an appropriate level, preservation of mobility, self-reliance and autonomy of each individual. The ability to participate in social activities as well as improvement in the quality of life need to be the focus of pharmacological and non-pharmacological treatment.

Guideline "diagnosis and non interventional therapy of neuropathic pain" of the German Society of Neurology (deutsche Gesellschaft für Neurologie)

2019 the DGN (Deutsche Gesellschaft für Neurology) published a new guideline on the diagnosis and non-interventional therapy of neuropathic pain of any etiology excluding trigeminal neuralgia and CRPS (complex regional pain syndrome). Neuropathic pain occurs after lesion or damage of the somatosensory system. Besides clinical examination several diagnostic procedures are recommended to assess the function of nociceptive A-delta and C-Fibers (skin biopsy, quantitative sensory testing, Laser-evoked potentials, Pain-evoked potentials, corneal confocal microscopy, axon reflex testing). First line treatment in neuropathic pain is pregabalin, gabapentin, duloxetine and amitriptyline. Second choice drugs are topical capsaicin and lidocaine, which can also be considered as primary treatment in focal neuropathic pain. Opioids are considered as third choice treatment. Botulinum toxin can be considered as a third choice drug for focal limited pain in specialized centers only. Carbamazepine and oxcarbazepine cannot be generally  recommended, but might be helpful in single cases. In Germany, cannabinoids can be prescribed, but only after approval of reimbursement. However, the use is not recommended, and can only be considered as off-label therapy within a multimodal therapy concept.