Neuropathic pain clinical trials: factors associated with decreases in estimated drug efficacy

Test-retest and interrater reliability of experimental within-subject variability of pain reports as assessed by the focused analgesia selection test

Introduction

Within-subject variability (WSV) of pain intensity reports has been shown to predict the placebo response. The focused analgesia selection test (FAST), which allows to experimentally assess WSV of pain reports, has been used as a screening tool to identify participants who are likely to have a strong placebo response in drug-development clinical trials. Yet, the reliability of FAST has not been reported.

Objectives

To assess test-retest and interrater reliability of the FAST outcomes. To mimic pharma-sponsored clinical trials, we enlisted inexperienced assessors who underwent limited training.

Methods

Healthy volunteers performed the FAST twice within a week and were randomly assigned to either the test-retest group or the interrater group. T-tests, partial Pearson correlations, intraclass correlations (ICC), and Bland-Altman plots were generated to assess FAST outcomes' reliability.

Results

Sixty-three participants completed the study and were assigned to the test-retest (N = 33) or interrater (N = 30) arms. No statistically significant differences in the FAST outcomes were detected between the 2 sessions, except for the FAST covariance (FAST CoV) in the interrater assessment (P = 0.009). Test-retest reliabilities of the FAST-main outcomes were r = 0.461, ICC = 0.385 for the FAST R 2 and r = 0.605, ICC = 0.539 for the FAST ICC and in the interrater cohort, they were FAST R 2: r = 0.321, ICC = 0.337 and FAST ICC: r = 0.355, ICC = 0.330.

Conclusion

Using inexperienced assessors, the FAST outcomes test-retest ranged from moderate to strong, whereas the interrater reliability ranged from weak to poor. These results highlight the importance of adequately training study staff members before using this tool in multicentre clinical trials.

Methods for pragmatic randomized clinical trials of pain therapies: IMMPACT statement

ABSTRACT

Pragmatic, randomized, controlled trials hold the potential to directly inform clinical decision making and health policy regarding the treatment of people experiencing pain. Pragmatic trials are designed to replicate or are embedded within routine clinical care and are increasingly valued to bridge the gap between trial research and clinical practice, especially in multidimensional conditions, such as pain and in nonpharmacological intervention research. To maximize the potential of pragmatic trials in pain research, the careful consideration of each methodological decision is required. Trials aligned with routine practice pose several challenges, such as determining and enrolling appropriate study participants, deciding on the appropriate level of flexibility in treatment delivery, integrating information on concomitant treatments and adherence, and choosing comparator conditions and outcome measures. Ensuring data quality in real-world clinical settings is another challenging goal. Furthermore, current trials in the field would benefit from analysis methods that allow for a differentiated understanding of effects across patient subgroups and improved reporting of methods and context, which is required to assess the generalizability of findings. At the same time, a range of novel methodological approaches provide opportunities for enhanced efficiency and relevance of pragmatic trials to stakeholders and clinical decision making. In this study, best-practice considerations for these and other concerns in pragmatic trials of pain treatments are offered and a number of promising solutions discussed. The basis of these recommendations was an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) meeting organized by the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks.

Treatment of Painful Diabetic Neuropathy with 10 kHz Spinal Cord Stimulation: Long-Term Improvements in Hemoglobin A1c, Weight, and Sleep Accompany Pain Relief for People with Type 2 Diabetes

Purpose

The recent SENZA-PDN study showed that high-frequency (10kHz) spinal cord stimulation (SCS) provided significant, durable pain relief for individuals with painful diabetic neuropathy (PDN), along with secondary benefits, including improved sleep quality and HRQoL. Given that metabolic factors and chronic neuropathic pain are related, we evaluated potential secondary effects of 10kHz SCS on hemoglobin A1c (HbA1c) and weight in SENZA-PDN participants with type 2 diabetes (T2D).

Patients and Methods

This analysis included 144 participants with T2D and lower limb pain due to PDN who received 10kHz SCS during the SENZA-PDN study. Changes in HbA1c, weight, pain intensity, and sleep were evaluated over 24 months, with participants stratified according to preimplantation HbA1c (>7% and >8%) and body mass index (BMI; ≥30 and ≥35 kg/m2).

Results

At 24 months, participants with preimplantation HbA1c >7% and >8% achieved clinically meaningful and statistically significant mean reductions in HbA1c of 0.5% (P = 0.031) and 1.1% (P = 0.004), respectively. Additionally, we observed a significant mean weight loss of 3.1 kg (P = 0.003) across all study participants. In subgroups with BMI ≥30 and ≥35 kg/m2, weight reductions at 24 months were 4.1 kg (P = 0.001) and 5.4 kg (P = 0.005), respectively. These reductions were accompanied by a mean pain reduction of 79.8% and a mean decrease in pain interference with sleep of 65.2% at 24 months across all cohorts.

Conclusion

This is the first study of SCS to demonstrate long-term, significant, and clinically meaningful reductions in HbA1c and weight in study participants with PDN and T2D, particularly among those with elevated preimplantation HbA1c and BMI. Although the mechanism for these improvements has yet to be established, the results suggest possible direct and indirect metabolic benefits with 10kHz SCS in addition to durable pain relief.

Trial Registration

ClincalTrials.gov Identifier, NCT03228420.

Efficacy and Safety of Trazodone and Gabapentin Fixed-Dose Combination in Patients Affected by Painful Diabetic Neuropathy: Randomized, Controlled, Dose-Finding Study

INTRODUCTION

Up to 50% of diabetic patients with neuropathy suffer from chronic pain, namely painful diabetic neuropathy (PDN), an unmet medical need with significant impact on quality of life. Gabapentin is widely used for PDN, albeit with frequent dose-limiting effects. Trazodone, an antidepressant with multi-modal action, has shown promising results when given at low doses as an add-on to gabapentin. Upon previous clinical trials and experimental evidence, a fixed-dose combination (FDC) of both compounds, at low doses, was developed for neuropathic pain.

METHODS

This was a phase II, randomized, double-blind, placebo and reference controlled, dose-finding, multicenter, international, prospective study. Male and female diabetic patients aged 18-75 years and affected by PDN were eligible for enrolment. Patients were randomized (1:1:1:1:2 ratio) to trazodone and gabapentin (Trazo/Gaba) 2.5/25 mg t.i.d. for 8 weeks, Trazo/Gaba 5/50 mg t.i.d. for 8 weeks, Trazo/Gaba 10/100 mg t.i.d. for 8 weeks, gabapentin (Gaba), or placebo (PLB). The aim of the study was to collect preliminary information on the effect of the 3 different FDCs of Trazo/Gaba on pain intensity based on the 11-point numeric rating score (NRS) after 8 weeks of treatment. The secondary objectives were the evaluation of the percentage of responders, neuropathic pain symptoms, anxiety, sleep, quality of life, safety, and tolerability. The primary efficacy endpoint was evaluated with last observation carried out forward (LOCF), using an analysis of covariance (ANCOVA), including treatment and centers as factors and baseline as covariate and applying linear contrast test, excluding the active treatment. Only if the linear contrast test was significant (p < 0.05), the step-down Dunnett test would be used to determine the minimum effective dose significantly different from PLB. If linearity was not verified, an adjusted ANCOVA model and comparisons with Dunnett test were performed. Before the application of the ANCOVA model, the non-significance of interaction treatment per baseline was verified.

RESULTS

A total of 240 patients were included in the modified intention-to-treat (m-ITT) population: 39 in Trazo/Gaba 2.5/25 mg, 38 in Trazo/Gaba 5/50 mg, 37 in Trazo/Gaba 10/100 mg, 83 in PLB, and 43 in Gaba. After 8 weeks of treatment, changes of the average daily pain score based on the 11-point NRS from baseline were - 2.52 ± 2.31 in Trazo/Gaba 2.5/25 mg group, - 2.24 ± 1.96 in Trazo/Gaba 5/50 mg group, - 2.46 ± 2.12 in Trazo/Gaba 10/100 mg group, - 1.92 ± 2.21 in Gaba group, and - 2.02 ± 1.95 in the PLB group. The linear contrast test did not result in significant differences (p > 0.05) among treatment groups. Consequently, the minimum effective dose against PLB was not determined. The multiple comparison with Dunnett adjustment did not show any statistically significant differences vs. PLB after 8 weeks of treatment: Trazo/Gaba 2.5/25 mg (95% confidence interval (CI) - 1.2739, 0.2026; p = 0.1539); Trazo/Gaba 5/50 mg (95% CI - 0.9401, 0.5390; p = 0.5931); Trazo/Gaba 10/100 mg (95% CI - 1.0342, 0.4582; p = 0.4471). However, patients receiving the lowest dose of Trazo/Gaba 2.5/25 mg showed a statistically significant difference to PLB after 6 weeks of treatment (95% CI - 1.6648, - 0.2126; p = 0.0116). Positive results were also found for responder patients, other items related to the pain, anxiety, depression, sleep, and quality of life, consistently in favor to the lowest Trazo/Gaba FDC. Two serious adverse events (SAEs) occurred but were judged unrelated to the study treatment. Treatment-emergent adverse events (TEAEs) were mainly mild-to-moderate in intensity and involved primarily nervous system, gastrointestinal disorders, and investigations.

CONCLUSIONS

The primary end point of the study was the change from baseline of the average daily pain score based on the 11-point NRS after 8 weeks of treatment. While the primary endpoint was not reached, patients treated with Trazo/Gaba 2.5/25 mg t.i.d. showed statistically significant improvement of pain and other scores after 6 weeks and reported consistent better results in comparison to PLB on primary and secondary endpoints for the overall study duration. According to these results, the lowest dose of Trazo/Gaba FDC may be the best candidate for further clinical development to confirm the potential benefits of the FDC drug for this condition.

CLINICAL TRIAL REGISTRATION

NCT03749642.

Sex-Gender Differences Are Completely Neglected in Treatments for Neuropathic Pain

As sex-gender differences have been described in the responses of patients to certain medications, we hypothesized that the responses to medications recommended for neuropathic pain may differ between men and women. We conducted a literature review to identify articles reporting potential sex-gender differences in the efficacy and safety of these medications. Only a limited number of studies investigated potential sex-gender differences. Our results show that women seem to achieve higher blood concentrations than men during treatment with amitriptyline, nortriptyline, duloxetine, venlafaxine, and pregabalin. Compared to men, higher rates of women develop side effects during treatment with gabapentin, lidocaine, and tramadol. Globally, the sex-gender differences would suggest initially administering smaller doses of these medications to women with neuropathic pain compared to those administered to men. However, most of these differences have been revealed by studies focused on the treatment of other diseases (e.g., depression). Studies focused on neuropathic pain have overlooked potential sex-gender differences in patient responses to medications. Despite the fact that up to 60% of patients with neuropathic pain fail to achieve an adequate response to medications, the potential role of sex-gender differences in the efficacy and safety of pharmacotherapy has not adequately been investigated. Targeted studies should be implemented to facilitate personalized treatments for neuropathic pain.

Evaluating the Antihyperalgesic Potential of Sildenafil-Metformin Combination and Its Impact on Biochemical Markers in Alloxan-Induced Diabetic Neuropathy in Rats

(1) Background: Globally, about 600 million people are afflicted with diabetes, and one of its most prevalent complications is neuropathy, a debilitating condition. At the present time, the exploration of novel therapies for alleviating diabetic-neuropathy-associated pain is genuinely captivating, considering that current therapeutic options are characterized by poor efficacy and significant risk of side effects. In the current research, we evaluated the antihyperalgesic effect the sildenafil (phosphodiesterase-5 inhibitor)-metformin (antihyperglycemic agent) combination and its impact on biochemical markers in alloxan-induced diabetic neuropathy in rats. (2) Methods: This study involved a cohort of 70 diabetic rats and 10 non-diabetic rats. Diabetic neuropathy was induced by a single dose of 130 mg/kg alloxan. The rats were submitted to thermal stimulus test using a hot-cold plate and to tactile stimulus test using von Frey filaments. Moreover, at the end of the experiment, the animals were sacrificed and their brains and livers were collected to investigate the impact of this combination on TNF-α, IL-6, nitrites and thiols levels. (3) Results: The results demonstrated that all sildenafil-metformin combinations decreased the pain sensitivity in the von Frey test, hot plate test and cold plate test. Furthermore, alterations in nitrites and thiols concentrations and pro-inflammatory cytokines (specifically TNF-α and IL-6) were noted following a 15-day regimen of various sildenafil-metformin combinations. (4) Conclusions: The combination of sildenafil and metformin has a synergistic effect on alleviating pain in alloxan-induced diabetic neuropathy rats. Additionally, the combination effectively decreased inflammation, inhibited the rise in NOS activity, and provided protection against glutathione depletion.

A systematic review and meta-analysis of randomized controlled head-to-head trials of recommended drugs for neuropathic pain

Neuropathic pain is a challenging chronic pain condition. Limited knowledge exists regarding the relative effectiveness of pharmacological treatments, and differences in trial design and impact of the placebo response preclude indirect comparisons of efficacy between drug classes. The purpose of this systematic review and meta-analysis of head-to-head trials was to compare the efficacy and tolerability of drugs recommended for neuropathic pain. We conducted a systematic review and meta-analysis of direct-comparison double-blind randomized trials. Primary outcomes were mean change in pain intensity and number of responders with a 50% reduction in pain intensity. Secondary outcomes encompassed quality of life, sleep, emotional functioning, and number of dropouts because of adverse events. We included 30 trials (4087 patients), comprising 16 crossover and 14 parallel-group design studies. All studies were conducted in adults, and the majority were investigator-initiated trials. We found moderate-quality evidence for equivalence (no clinically relevant difference) between tricyclic antidepressants (TCA) and gabapentin/pregabalin with a combined mean difference in pain score of 0.10 (95% CI -0.13 to 0.32). We could not document differences between TCA and serotonin-noradrenaline reuptake inhibitors (SNRI), between SNRI and gabapentin/pregabalin, or between opioids and TCA (low quality of evidence). We found more dropouts because of adverse events with SNRI and opioids compared with TCA (low quality of evidence). We did not identify any studies that included topical treatments. This systematic review of direct-comparison studies found evidence for equivalence between TCA and gabapentin/pregabalin and fewer dropouts with TCA than SNRI and opioids.

Transcranial Magnetic Stimulation to Treat Neuropathic Pain: A Bibliometric Analysis

Neuropathic pain is caused by a lesion or disease of the somatosensory system and is one of the most incapacitating pain types, representing a significant non-met medical need. Due to the increase in research in the field and since innovative therapeutic strategies are required, namely in intractable neuropathic pain, neurostimulation has been used. Within this approach, transcranial magnetic stimulation (TMS) that uses a transient magnetic field to produce electrical currents over the cortex emerges as a popular method in the literature. Since this is an area in expansion and due to the putative role of TMS, we performed a bibliometric analysis in Scopus with the primary objective of identifying the scientific production related to the use of TMS to manage neuropathic pain. The research had no restrictions, and the analysis focused on the characteristics of the literature retrieved, scientific collaboration and main research topics from inception to 6 July 2023. A total of 474 articles were collected. A biggest co-occurrence between the terms "neuropathic pain" and "transcranial magnetic stimulation" was obtained. The journal "Clinical Neurophysiology" leads the Top 5 most productive sources. The United States is the most productive country, with 50% of US documents being "review articles", followed by France, with 56% of French documents being "original articles". Lefaucheur, JP and Saitoh, Y are the two most influential authors. The most frequent type of document was "original article". Most of the studies (34%) that identified the neuropathic pain type focused on traumatic neuropathic pain, although a large proportion (38%) did not report the neuropathic pain type. This study allows us to provide a general overview of the field of TMS application for neuropathic pain and is useful for establishing future directions of research in this field.

Quantification of stimulus-evoked tactile allodynia in free moving mice by the chainmail sensitivity test

Chronic pain occurs at epidemic levels throughout the population. Hypersensitivity to touch, is a cardinal symptom of chronic pain. Despite dedicated research for over a century, quantifying this hypersensitivity has remained impossible at scale. To address these issues, we developed the Chainmail Sensitivity Test (CST). Our results show that control mice spend significantly more time on the chainmail portion of the device than mice subject to neuropathy. Treatment with gabapentin abolishes this difference. CST-derived data correlate well with von Frey measurements and quantify hypersensitivity due to inflammation. Our study demonstrates the potential of the CST as a standardized tool for assessing mechanical hypersensitivity in mice with minimal operator input.

A novel theta-controlled vibrotactile brain-computer interface to treat chronic pain: a pilot study

Limitations in chronic pain therapies necessitate novel interventions that are effective, accessible, and safe. Brain-computer interfaces (BCIs) provide a promising modality for targeting neuropathology underlying chronic pain by converting recorded neural activity into perceivable outputs. Recent evidence suggests that increased frontal theta power (4-7 Hz) reflects pain relief from chronic and acute pain. Further studies have suggested that vibrotactile stimulation decreases pain intensity in experimental and clinical models. This longitudinal, non-randomized, open-label pilot study's objective was to reinforce frontal theta activity in six patients with chronic upper extremity pain using a novel vibrotactile neurofeedback BCI system. Patients increased their BCI performance, reflecting thought-driven control of neurofeedback, and showed a significant decrease in pain severity (1.29 ± 0.25 MAD, p = 0.03, q = 0.05) and pain interference (1.79 ± 1.10 MAD p = 0.03, q = 0.05) scores without any adverse events. Pain relief significantly correlated with frontal theta modulation. These findings highlight the potential of BCI-mediated cortico-sensory coupling of frontal theta with vibrotactile stimulation for alleviating chronic pain.

Comparative Efficacy and Safety of Antidepressants for Patients with Chronic Back Pain: A Network Meta-Analysis

Various antidepressants have introduced in clinical practice for pain management, but it is important to understand how to properly use them. We therefore performed a systematic review and network meta-analysis to compare and rank the efficacy and safety of antidepressants for patients with chronic back pain. We identified eligible randomized controlled trials (RCTs) that investigated the efficacy and safety of antidepressants for chronic back pain from PubMed, Embase, the Cochrane Library, and ClinicalTrials.gov, searching from inception to May 2023. Six categories of antidepressants for the treatment of chronic back pain were included, and the surface under the cumulative ranking probabilities was applied to rank the treatment strategies. Overall, we selected 19 RCTs recruiting 2903 patients for the meta-analysis. Tricyclic antidepressants presented the best relative effects for relief in pain score (surface under the cumulative ranking, 84.4%). The results of pairwise comparison analyses found the use of serotonin-noradrenaline reuptake inhibitors (SNRIs) significantly reduced pain score and low disability score compared with placebo, irrespective of treatment duration. Noradrenaline-dopamine reuptake inhibitors (relative risk [RR], 2.80; 95% confidence interval [CI], 1.30-6.03; P = .008) and SNRIs (RR, 1.17; 95% CI, 1.07-1.27; P < .001) significantly increased the risk of adverse events. SNRIs were associated with an increased risk of withdrawal due to adverse events (RR, 2.37; 95% CI, 1.64-3.43; P < .001). This study found that antidepressants are more efficacious than placebos for treating chronic back pain, and tricyclic antidepressants are the most likely medications that lead to pain relief.

Response to experimental cold-induced pain discloses a resistant category among endurance athletes, with a distinct profile of pain-related behavior and GABAergic EEG markers: a case-control preliminary study

Pain is a major public health problem worldwide, with a high rate of treatment failure. Among promising non-pharmacological therapies, physical exercise is an attractive, cheap, accessible and innocuous method; beyond other health benefits. However, its highly variable therapeutic effect and incompletely understood underlying mechanisms (plausibly involving the GABAergic neurotransmission) require further research. This case-control study aimed to investigate the impact of long-lasting intensive endurance sport practice (≥7 h/week for the last 6 months at the time of the experiment) on the response to experimental cold-induced pain (as a suitable chronic pain model), assuming that highly trained individual would better resist to pain, develop advantageous pain-copying strategies and enhance their GABAergic signaling. For this purpose, clinical pain-related data, response to a cold-pressor test and high-density EEG high (Hβ) and low beta (Lβ) oscillations were documented. Among 27 athletes and 27 age-adjusted non-trained controls (right-handed males), a category of highly pain-resistant participants (mostly athletes, 48.1%) was identified, displaying lower fear of pain, compared to non-resistant non-athletes. Furthermore, they tolerated longer cold-water immersion and perceived lower maximal sensory pain. However, while having similar Hβ and Lβ powers at baseline, they exhibited a reduction between cold and pain perceptions and between pain threshold and tolerance (respectively -60% and - 6.6%; -179.5% and - 5.9%; normalized differences), in contrast to the increase noticed in non-resistant non-athletes (+21% and + 14%; +23.3% and + 13.6% respectively). Our results suggest a beneficial effect of long-lasting physical exercise on resistance to pain and pain-related behaviors, and a modification in brain GABAergic signaling. In light of the current knowledge, we propose that the GABAergic neurotransmission could display multifaceted changes to be differently interpreted, depending on the training profile and on the homeostatic setting (e.g., in pain-free versus chronic pain conditions). Despite limitations related to the sample size and to absence of direct observations under acute physical exercise, this precursory study brings into light the unique profile of resistant individuals (probably favored by training) allowing highly informative observation on physical exercise-induced analgesia and paving the way for future clinical translation. Further characterizing pain-resistant individuals would open avenues for a targeted and physiologically informed pain management.

Placebo and nocebo responses in painful diabetic neuropathy: systematic review and meta-analysis

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.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.

Placebo effects in osteoarthritis: implications for treatment and drug development

Osteoarthritis (OA) is the most common form of arthritis worldwide, affecting ~500 million people, yet there are no effective treatments to halt its progression. Without any structure-modifying agents, management of OA focuses on ameliorating pain and improving function. Treatment approaches typically have modest efficacy, and many patients have contraindications to recommended pharmacological treatments. Drug development for OA is hindered by the gradual and progressive nature of the disease and the targeting of established disease in clinical trials. Additionally, new medications for OA cannot receive regulatory approval without demonstrating improvements in both structure (pathological features of OA) and symptoms (reduced pain and/or improved function). In clinical trials, people with OA show high 'placebo responses', which hamper the ability to identify new effective treatments. Placebo responses refer to the individual variability in response to placebos given in the context of clinical trials and other settings. Placebo effects refer specifically to short-lasting improvements in symptoms that occur because of physiological changes. To mitigate the effects of the placebo phenomenon, we must first understand what it is, how it manifests, how to identify placebo responders in OA trials and how these insights can be used to improve clinical trials in OA. Leveraging placebo responses and effects in clinical practice might provide additional avenues to augment symptom management of OA.

New perspectives in diabetic neuropathy

Diabetes prevalence continues to climb with the aging population. Type 2 diabetes (T2D), which constitutes most cases, is metabolically acquired. Diabetic peripheral neuropathy (DPN), the most common microvascular complication, is length-dependent damage to peripheral nerves. DPN pathogenesis is complex, but, at its core, it can be viewed as a state of impaired metabolism and bioenergetics failure operating against the backdrop of long peripheral nerve axons supported by glia. This unique peripheral nerve anatomy and the injury consequent to T2D underpins the distal-to-proximal symptomatology of DPN. Earlier work focused on the impact of hyperglycemia on nerve damage and bioenergetics failure, but recent evidence additionally implicates contributions from obesity and dyslipidemia. This review will cover peripheral nerve anatomy, bioenergetics, and glia-axon interactions, building the framework for understanding how hyperglycemia and dyslipidemia induce bioenergetics failure in DPN. DPN and painful DPN still lack disease-modifying therapies, and research on novel mechanism-based approaches is also covered.

Cortical Mechanisms Underlying Immersive Interactive Virtual Walking Treatment for Amelioration of Neuropathic Pain after Spinal Cord Injury: Findings from a Preliminary Investigation of Thalamic Inhibitory Function

BACKGROUND

Neuropathic pain following spinal cord injury (SCI) affects approximately 60% of individuals with SCI. Effective pharmacological and non-pharmacological treatments remain elusive. We recently demonstrated that our immersive virtual reality walking intervention (VRWalk) may be effective for SCI NP. Additionally, we found that SCI NP may result from a decrease in thalamic γ-aminobutyric-acid (GABA), which disturbs central sensorimotor processing.

OBJECTIVE

While we identified GABAergic changes associated with SCI NP, a critical outstanding question is whether a decrease in SCI NP generated by our VRWalk intervention causes GABA content to rise.

METHOD

A subset of participants (n = 7) of our VRWalk trial underwent magnetic resonance spectroscopy pre- and post-VRWalk intervention to determine if the decrease in SCI NP is associated with an increase in thalamic GABA.

RESULTS

The findings revealed a significant increase in thalamic GABA content from pre- to post-VRWalk treatment.

CONCLUSION

While the current findings are preliminary and should be interpreted with caution, pre- to post-VRWalk reductions in SCI NP may be mediated by pre- to post-treatment increases in thalamic GABA by targeting and normalizing maladaptive sensorimotor cortex reorganization. Understanding the underlying mechanisms of pain recovery can serve to validate the efficacy of home-based VR walking treatment as a means of managing pain following SCI. Neuromodulatory interventions aimed at increasing thalamic inhibitory function may provide more effective pain relief than currently available treatments.

Long-term efficacy of high-frequency (10 kHz) spinal cord stimulation for the treatment of painful diabetic neuropathy: 24-Month results of a randomized controlled trial

AIMS

To evaluate the long-term efficacy of high-frequency (10 kHz) spinal cord stimulation (SCS) for treating refractory painful diabetic neuropathy (PDN).

METHODS

The SENZA-PDN study was a prospective, multicenter, randomized controlled trial that compared conventional medical management (CMM) alone with 10 kHz SCS plus CMM (10 kHz SCS+CMM) in 216 patients with refractory PDN. After 6 months, participants with insufficient pain relief could cross over to the other treatment. In total, 142 patients with a 10 kHz SCS system were followed for 24 months, including 84 initial 10 kHz SCS+CMM recipients and 58 crossovers from CMM alone. Assessments included pain intensity, health-related quality of life (HRQoL), sleep, and neurological function. Investigators assessed neurological function via sensory, reflex, and motor tests. They identified a clinically meaningful improvement relative to the baseline assessment if there was a significant persistent improvement in neurological function that impacted the participant's well-being and was attributable to a neurological finding.

RESULTS

At 24 months, 10 kHz SCS reduced pain by a mean of 79.9% compared to baseline, with 90.1% of participants experiencing ≥50% pain relief. Participants had significantly improved HRQoL and sleep, and 65.7% demonstrated clinically meaningful neurological improvement. Five (3.2%) SCS systems were explanted due to infection.

CONCLUSIONS

Over 24 months, 10 kHz SCS provided durable pain relief and significant improvements in HRQoL and sleep. Furthermore, the majority of participants demonstrated neurological improvement. These long-term data support 10 kHz SCS as a safe and highly effective therapy for PDN.

TRIAL REGISTRATION

ClincalTrials.gov Identifier, NCT03228420.

Advances and challenges in neuropathic pain: a narrative review and future directions

Over the past few decades, substantial advances have been made in neuropathic pain clinical research. An updated definition and classification have been agreed. Validated questionnaires have improved the detection and assessment of acute and chronic neuropathic pain; and newer neuropathic pain syndromes associated with COVID-19 have been described. The management of neuropathic pain has moved from empirical to evidence-based medicine. However, appropriately targeting current medications and the successful clinical development of drugs acting on new targets remain challenging. Innovative approaches to improving therapeutic strategies are required. These mainly encompass rational combination therapy, drug repurposing, non-pharmacological approaches (such as neurostimulation techniques), and personalised therapeutic management. This narrative review reports historical and current perspectives regarding the definitions, classification, assessment, and management of neuropathic pain and explores potential avenues for future research.

Dynamic effects of prognostic factors and individual survival prediction for amyotrophic lateral sclerosis disease

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons, with broad heterogeneity in disease progression and survival in different patients. Therefore, an accurate prediction model will be crucial to implement timely interventions and prolong patient survival time.

METHODS

A total of 1260 ALS patients from the PRO-ACT database were included in the analysis. Their demographics, clinical variables, and death reports were included. We constructed an ALS dynamic Cox model through the landmarking approach. The predictive performance of the model at different landmark time points was evaluated by calculating the area under the curve (AUC) and Brier score.

RESULTS

Three baseline covariates and seven time-dependent covariates were selected to construct the ALS dynamic Cox model. For better prognostic analysis, this model identified dynamic effects of treatment, albumin, creatinine, calcium, hematocrit, and hemoglobin. Its prediction performance (at all landmark time points, AUC ≥ 0.70 and Brier score ≤ 0.12) was better than that of the traditional Cox model, and it predicted the dynamic 6-month survival probability according to the longitudinal information of individual patients.

INTERPRETATION

We developed an ALS dynamic Cox model with ALS longitudinal clinical trial datasets as the inputs. This model can not only capture the dynamic prognostic effect of both baseline and longitudinal covariates but also make individual survival predictions in real time, which are valuable for improving the prognosis of ALS patients and providing a reference for clinicians to make clinical decisions.

Predicting placebo analgesia in patients with chronic pain using natural language processing: a preliminary validation study

ABSTRACT

Patients with chronic pain show large placebo effects in clinical trials, and inert pills can lead to clinically meaningful analgesia that can last from days to weeks. Whether the placebo response can be predicted reliably, and how to best predict it, is still unknown. We have shown previously that placebo responders can be identified through the language content of patients because they speak about their life, and their pain, after a placebo treatment. In this study, we examine whether these language properties are present before placebo treatment and are thus predictive of placebo response and whether a placebo prediction model can also dissociate between placebo and drug responders. We report the fine-tuning of a language model built based on a longitudinal treatment study where patients with chronic back pain received a placebo (study 1) and its validation on an independent study where patients received a placebo or drug (study 2). A model built on language features from an exit interview from study 1 was able to predict, a priori, the placebo response of patients in study 2 (area under the curve = 0.71). Furthermore, the model predicted as placebo responders exhibited an average of 30% pain relief from an inert pill, compared with 3% for those predicted as nonresponders. The model was not able to predict who responded to naproxen nor spontaneous recovery in a no-treatment arm, suggesting specificity of the prediction to placebo. Taken together, our initial findings suggest that placebo response is predictable using ecological and quick measures such as language use.

Predicting Treatment Responses in Patients With Osteoarthritis: Results From Two Phase III Tanezumab Randomized Clinical Trials

Prediction of treatment responses is essential to move forward translational science. Our question was to identify patient-based variables that predicted responses to treatments. We conducted secondary analyses on pooled data from two randomized phase III clinical trials (NCT02697773 and NCT02709486) conducted in participants with moderate to severe osteoarthritis randomized to subcutaneous placebo (n = 514) or tanezumab 2.5 mg (n = 514). We used gradient boosted regression trees to identify variables that predicted Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Pain subscale scores at Week 16 and marginal plots to determine the directional relationship between each variable category and responses to placebo or tanezumab within the models. We also used Virtual Twins models to identify potential subgroups of response to the active treatment vs. placebo. We found that responses to placebo were predicted by baseline WOMAC Physical Function, baseline WOMAC Pain, the radiographic classification of the index joint, and the standard deviation of diary pain scores at baseline. In contrast, baseline WOMAC Pain along with failure of prior medications, duration of disease, and standard deviation of diary pain scores at baseline were predictive of tanezumab responses as expressed by the WOMAC Pain scores at Week 16. Those who responded to tanezumab vs. placebo were identified based on the radiographic classification of the index joint and either age or smoking status. These secondary-data analyses identified distinct and common patient-based variables to predict response to placebo or tanezumab. These findings will inform the design of future clinical trials, helping to move forward clinical pharmacology and translational science.

Oral capsules of tetra-hydro-cannabinol (THC), cannabidiol (CBD) and their combination in peripheral neuropathic pain treatment

BACKGROUND

Cannabinoids are often prescribed for neuropathic pain, but the evidence-based recommendation is 'weak against'.

OBJECTIVES

The aim was to examine the effect of two cannabinoids and their combination in peripheral neuropathic pain.

METHODS

This was a randomized, double-blind, trial with treatment arms for cannabidiol (CBD), tetra-hydro-cannabinol (THC), CBD and THC combination (CBD/THC), and placebo in a 1:1:1:1 ratio and flexible drug doses (CBD 5-50 mg, THC 2.5-25 mg, and CBD/THC 5 mg/2.5 mg-50 mg/25 mg). Treatment periods of 8-week duration were proceeded by 1 week for baseline observations. Patients with painful polyneuropathy, post-herpetic neuralgia and peripheral nerve injury (traumatic or surgical) failing at least one previous evidence-based pharmacological treatment were eligible for inclusion. The primary outcome was the change in weekly average of daily pain measured with a numeric rating scale (NRS). Trail Making Test (TMT) was used as one of the tests of mental functioning.

RESULTS

In all, 145 patients were included in the study of which 118 were randomized and 115 included in the intention-to-treat analysis. None of the treatments reduced pain compared to placebo (p = 0.04-0.60). Effect sizes as estimated in week 8 (positive values worse and negative better than placebo) were CBD mean 1.14 NRS points (95% CI 0.11-2.19), THC 0.38 (CI -0.65 to 1.4) and CBD/THC -0.12 (-1.13 to 0.89).

CONCLUSIONS

CBD, THC and their combination did not relieve peripheral neuropathic pain in patients failing at least one previous evidence-based treatment for neuropathic pain.

Mirror peripheral neuropathy and unilateral chronic neuropathic pain: insights from asymmetric neurological patterns in leprosy

ABSTRACT

Leprosy-related multiple mononeuropathy offers a pattern of impairment where neuropathy with and without neuropathic pain (NeP) are present in the same individual, thus allowing to investigate peripheral sensory and innervation in both conditions. This cross-sectional study collected data on clinical and neurological examination, pain assessment questionnaires, quantitative sensory test, and intraepidermal nerve fiber density of patients with leprosy and divided the cohort into 2 groups: with NeP (P+) and without NeP (P-). Furthermore, we assessed mirror body areas in the same NeP individuals with bilateral neuropathy also presenting unilateral NeP. Pain-free patients having unilateral neuropathy were controls. A total of 37 P+ and 22 P- patients were evaluated. Limb areas with NeP had signs of C-fiber dysfunction and hyperesthesia on quantitative sensory testing compared with limb areas having neuropathy without NeP. Skin denervation was found in all patients with leprosy. Comparisons of limbs with and without neuropathy and with and without NeP revealed that higher heat pain thresholds (HPTs) were associated with neuropathic pain areas, whereas less altered HPT was correlated with higher fiber density. Furthermore, a relationship was found between time of leprosy treatment termination and more intense neuropathy, expressed by HPT increasing 0.03°C each month. As expected, interindividual comparisons failed to show differences in intraepidermal nerve fiber density and subepidermal plexus areas between P+ and P- patients ( P = 0.2980, P = 0.9044; respectively). Higher HPT and lower mechanical detection threshold were related to NeP. This study pointed out the relevance of intraindividual comparisons including mirror areas when assessing local changes in peripheral NeP.

Expectations for Improvement: A Neglected but Potentially Important Covariate or Moderator for Chronic Pain Clinical Trials

Variability in pain-related outcomes can hamper assay sensitivity of chronic pain clinical trials. Expectations of outcome in such trials may account for some of this variability, and thereby impede development of novel pain treatments. Measurement of participants' expectations prior to initiating study treatment (active or placebo) is infrequent, variable, and often unvalidated. Efforts to optimize and standardize measurement, analysis, and management of expectations are needed. In this Focus Article, we provide an overview of research findings on the relationship between baseline expectations and pain-related outcomes in clinical trials of pharmacological and nonpharmacological pain treatments. We highlight the potential benefit of adjusting for participants' expectations in clinical trial analyses and draw on findings from patient interviews to discuss critical issues related to measurement of expectations. We conclude with suggestions regarding future studies focused on better understanding the utility of incorporating these measures into clinical trial analyses. PERSPECTIVE: This focus article provides an overview of the relationship between participants' baseline expectations and pain-related outcomes in the setting of clinical trials of chronic pain treatments. Systematic research focused on the measurement of expectations and the impact of adjusting for expectations in clinical trial analyses may improve assay sensitivity.

Pain Reduction With AbobotulinumtoxinA for the Treatment of Hallux Valgus in Adult Participants: Results of a Randomized and Placebo-Controlled Phase 2 Trial

AbobotulinumtoxinA (aboBoNT-A, Dysport® [Ipsen, Paris, France]) inhibits acetylcholine release at the neuromuscular junction and may modulate pain signaling in hallux valgus (HV). This randomized study (NCT03569098) included a double-blind phase (aboBoNT-A 300U, 500U or placebo injections into forefoot muscles) and an open-label aboBoNT-A treatment period in participants with an HV diagnosis and no HV surgery. The primary endpoint was change from baseline in numeric pain rating scale (NPRS) score at week 8. Secondary endpoints included change in NPRS (other time points) and proportion of participants with ≥20% reduction from baseline NPRS (responders). Post-hoc analyses assessed number of days in a 7-day evaluation period that participants spent in a lower pain state than at baseline. Participants received aboBoNT-A 300U (n = 63), 500U (n = 60) or placebo (n = 63). Superiority to placebo was not observed with either aboBoNT-A dose at week 8, thus the primary endpoint was unmet. At week 12, a trend toward efficacy was observed with aboBoNT-A 500U versus placebo and the proportion of participants with ≥20% reduction from baseline NPRS was greater with aboBoNT-A 500U versus placebo (p = .006). Participants in the aboBoNT-A 500U group spent more days with lower NPRS than their lowest baseline score, and with NPRS ≥2 points lower than their mean baseline NPRS at weeks 8 and 12 versus placebo (all p < .05; post-hoc). AboBoNT-A was well tolerated. Although the primary endpoint was unmet, other endpoints showed a nominal advantage for aboBoNT versus placebo for treatment of HV-related pain, particularly at week 12. Further clinical evaluation is needed to establish whether botulinum toxins represent a viable non-operative treatment option for HV-associated pain. PLAIN LANGUAGE SUMMARY: Hallux valgus is the medical name for a bunion, a foot deformity that can worsen over time. Patients with bunions experience pain and walking can become difficult, which can affect their quality of life. Foot support aids (e.g., braces, splints and inserts) are available, but surgery is the standard treatment. This study looked at how injections of a specific type of botulinum toxin, called abobotulinumtoxinA or "aboBoNT-A", into the foot may help to reduce pain in patients with bunions. The study included 186 patients aged 18 to 75 years who had not had surgery on their bunion. The researchers looked at how well the injections worked using scales that measure the pain levels the patient experienced. The main outcome was whether patients who had aboBoNT-A injections had less pain after 8 weeks than they did before treatment. The study included patients who were injected with saltwater (no treatment) to check that any treatment effect was real. Researchers also looked at the results after 12 weeks, as well as how many patients had less pain after treatment than before and how many days in a given week patients experienced less pain after treatment than they did before. There was no reduction in pain levels with aboBoNT-A injections after 8 weeks compared with no treatment. However, the other study outcomes suggested that aboBoNT-A resulted in a small benefit compared with no treatment, especially after 12 weeks. Further medical research is needed to establish whether botulinum toxins represent an alternative treatment to surgery for the pain associated with bunions.

EEG frequency band analysis in chronic neuropathic pain: A linear and nonlinear approach to classify pain severity

BACKGROUND AND OBJECTIVE

Chronic neuropathic pain (NP) is a chronic pain condition that severely impacts a patient's life. Pain management has proved to be inefficient due to a lack of a simple clinical tool that may identify and monitor NP. A low-cost, noninvasive tool that provides relevant information on NP is the electroencephalogram (EEG). However, the commonly used linear EEG features have proved to be limited in characterizing NP pathophysiology. This study sought to determine whether nonlinear EEG features such as approximate entropy (ApEn) would better differentiate pain severity than absolute band power.

METHODS

A non-parametric statistical approach based on the Brief Pain Inventory (BPI), along with linear and nonlinear EEG features, is proposed in this study. For this purpose, thirty-six chronic NP patients were recruited, and 22 channels were registered. Additionally, a control database of 13 participants with no NP was used as a reference, where 19 channels were registered. For both groups, EEG was recorded for 10 min in a resting state: 5 min with eyes open (EO) and 5 min with eyes closed (EC). Absolute band power and ApEn EEG features in the five clinical frequency bands (delta, theta, alpha, beta, and gamma) were estimated for all channels in both groups. As a result, 220-dimensional and 190-dimensional feature vectors were obtained for experimental and control classes respectively. For the experimental class, NP patients were grouped according to their BPI evaluation in three groups: low, moderate, and high pain. Finally, feature vectors were compared between groups using Kruskal Wallis and post-hoc Dunn's tests.

RESULTS

ApEn revealed significant statistical difference (p <=0.0001) in most frequency bands and conditions among the groups. In contrast, power had less significant differences between groups, particularly with EO. Furthermore, NP groups were notably clustered using only ApEn in theta, alpha, and beta bands.

CONCLUSIONS

The results indicate that ApEn effectively characterizes the different severities of chronic NP rather than the commonly used linear features. ApEn and other nonlinear techniques (e.g., spectral entropy, Shannon entropy) might be a more suitable methodology to monitor chronic NP experience.

The Constitutive Activity of Spinal 5-HT6 Receptors Contributes to Diabetic Neuropathic Pain in Rats

Diabetic neuropathy is often associated with chronic pain. Serotonin type 6 (5-HT₆) receptor ligands, particularly inverse agonists, have strong analgesic potential and may be new candidates for treating diabetic neuropathic pain and associated co-morbid cognitive deficits. The current study addressed the involvement of 5-HT₆ receptor constitutive activity and mTOR signaling in an experimental model of diabetic neuropathic pain induced by streptozocin (STZ) injection in the rat. Here, we show that mechanical hyperalgesia and associated cognitive deficits are suppressed by the administration of 5-HT₆ receptor inverse agonists or rapamycin. The 5-HT₆ receptor ligands also reduced tactile allodynia in traumatic and toxic neuropathic pain induced by spinal nerve ligation and oxaliplatin injection. Furthermore, both painful and co-morbid cognitive symptoms in diabetic rats are reduced by intrathecal delivery of a cell-penetrating peptide that disrupts 5-HT₆ receptor-mTOR physical interaction. These findings demonstrate the deleterious influence of the constitutive activity of spinal 5-HT₆ receptors upon painful and cognitive symptoms in diabetic neuropathic pains of different etiologies. They suggest that targeting the constitutive activity of 5-HT₆ receptors with inverse agonists or disrupting the 5-HT₆ receptor-mTOR interaction might be valuable strategies for the alleviation of diabetic neuropathic pain and cognitive co-morbidities.

Efficacy, safety, and tolerability of antidepressants for pain in adults: overview of systematic reviews

OBJECTIVE

To provide a comprehensive overview of the efficacy, safety, and tolerability of antidepressants for pain according to condition.

DESIGN

Overview of systematic reviews.

DATA SOURCES

PubMed, Embase, PsycINFO, and the Cochrane Central Register of Controlled Trials from inception to 20 June 2022.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Systematic reviews comparing any antidepressant with placebo for any pain condition in adults.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently extracted data. The main outcome measure was pain; for headache disorders it was frequency of headaches. Continuous pain outcomes were converted into a scale of 0 (no pain) to 100 (worst pain) and were presented as mean differences (95% confidence intervals). Dichotomous outcomes were presented as risk ratios (95% confidence intervals). Data were extracted from the time point closest to the end of treatment. When end of treatment was too variable across trials in a review, data were extracted from the outcome or time point with the largest number of trials and participants. Secondary outcomes were safety and tolerability (withdrawals because of adverse events). Findings were classified from each comparison as efficacious, not efficacious, or inconclusive. Certainty of evidence was assessed with the grading of recommendations assessment, development, and evaluation framework.

RESULTS

26 reviews (156 unique trials and >25 000 participants) were included. These reviews reported on the efficacy of eight antidepressant classes covering 22 pain conditions (42 distinct comparisons). No review provided high certainty evidence on the efficacy of antidepressants for pain for any condition. 11 comparisons (nine conditions) were found where antidepressants were efficacious, four with moderate certainty evidence: serotonin-norepinephrine reuptake inhibitors (SNRIs) for back pain (mean difference -5.3, 95% confidence interval -7.3 to -3.3), postoperative pain (-7.3, -12.9 to -1.7), neuropathic pain (-6.8, -8.7 to -4.8), and fibromyalgia (risk ratio 1.4, 95% confidence interval 1.3 to 1.6). For the other 31 comparisons, antidepressants were either not efficacious (five comparisons) or the evidence was inconclusive (26 comparisons).

CONCLUSIONS

Evidence of efficacy of antidepressants was found in 11 of the 42 comparisons included in this overview of systematic reviews-seven of the 11 comparisons investigated the efficacy of SNRIs. For the other 31 comparisons, antidepressants were either inefficacious or evidence on efficacy was inconclusive. The findings suggest that a more nuanced approach is needed when prescribing antidepressants for pain conditions.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022311073.

Off-label pharmacological treatment for neuropathic pain: A Delphi study by the Spanish Pain Society Neuropathic Pain Task Force

OBJECTIVES

The use of off-label pharmacotherapies for neuropathic pain (NP) is growing relating to the many unmet needs of patients. However, clinical guidelines fail to address it, and the available evidence is sparse and fragmented. We arranged a formal expert consensus to address this controversial issue and provide some guidance on judicious use.

METHODS

A two-round standard Delphi survey that involved pain clinic specialists with experience in the research and management of NP was done over an ad hoc 40-item questionnaire prepared by the authors. Consensus on each statement was defined as at least either 80% endorsement or rejection after the second round.

RESULTS

Forty-three and thirty-seven panelists participated in the first and second round, respectively. Consensus was reached in 34 out of 40 statements. Endorsed alternatives for unresponsive patients include non-gabapentinoid antiepileptics (oxcarbazepine and eslicarbazepine), venlafaxine, intravenous lidocaine (when doses can be optimized), and some vaporized cannabinoids (under appropriate surveillance). In addition, lacosamide, low-dose naltrexone, propofol, or ketamine could prove beneficial if subjected to more research. Other options were rejected, and there was controversy about the usefulness of topical preparations.

DISCUSSION

For patients who do not respond to standard NP treatments, some other viable pharmacological options can be attempted before advancing to other therapeutic stages. This may help patients who are reluctant to or have some contraindication for interventional therapies.

A meta-epidemiological study on the reported treatment effect of pregabalin in neuropathic pain trials over time

BACKGROUND

Pregabalin is a drug used to treat neuropathic pain, and its use has increased substantially since 2007. Early trials found a strong treatment effect on pain for post-herpetic neuralgia and diabetic neuropathy. However more recent studies have failed to replicate these results.

METHODS

This meta-epidemiological study aimed to assess change in the reported effectiveness of pregabalin in neuropathic pain trials over time, and if a change is present, determine any associated factors.

DATA SOURCES

We performed electronic searches for published trials in Medline, Embase and Cochrane Central Register of Controlled Trials databases; and unpublished trials on ClinicalTrials.gov, the EU Clinical Trials Register, and the Australia New Zealand Clinical Trials Registry with no restrictions.

STUDY SELECTION

We included randomized, placebo-controlled trials of pregabalin for treatment of neuropathic pain in adults.

DATA EXTRACTION AND SYNTHESIS

Two authors independently extracted study data: sample size and mean baseline, end-point and change in pain scores with measures of variance, trial end year, publication year, clinical indication, funding source, country of study, treatment duration, treatment dose, mean age and percentage male.

PRIMARY OUTCOME MEASURE

We defined treatment effect as the mean difference in pain scores between pregabalin and placebo groups at trial end-point and assessed for change over time using a random-effects meta-regression, adjusted for sample size, indication, treatment duration (weeks) and treatment dose.

RESULTS

We included 38 randomized published trials (9038 participants) and found that between 2003 and 2020, the reported treatment effect of pregabalin decreased by 0.4 points (95% CI: 0.3 to 0.6; p<0.001) on an 11-point pain scale per 5-year interval, from 1.3 points (95% CI: 1.0 to 1.5) in trials conducted in 2001-2005, to 0.3 (95% CI: -0.1 to 0.7) in trials conducted in 2016-2020. The reported treatment effect was lower than the minimal clinically important difference (MCID) of 1.7 points across all time periods, doses and most indications and was not found to be associated with study characteristics.

CONCLUSIONS

The reported treatment effect or analgesic efficacy of pregabalin from clinical trials has diminished over time. Clinical recommendations may need to be re-evaluated to account for recent evidence and to consider whether pregabalin therapy is indicated.

Maximizing treatment efficacy through patient stratification in neuropathic pain trials

Treatment of neuropathic pain remains inadequate despite the elucidation of multiple pathophysiological mechanisms and the development of promising therapeutic compounds. The lack of success in translating knowledge into clinical practice has discouraged pharmaceutical companies from investing in pain medicine; however, new patient stratification approaches could help bridge the translation gap and develop individualized therapeutic approaches. As we highlight in this article, subgrouping of patients according to sensory profiles and other baseline characteristics could aid the prediction of treatment success. Furthermore, novel outcome measures have been developed for patients with neuropathic pain. The extent to which sensory profiles and outcome measures can be employed in routine clinical practice and clinical trials and across distinct neuropathic pain aetiologies is yet to be determined. Improvements in animal models, drawing on our knowledge of human pain, and robust public-private partnerships will be needed to pave the way to innovative and effective pain medicine in the future.

Tuina for peripherally-induced neuropathic pain: A review of analgesic mechanism

Peripherally-induced neuropathic pain (pNP) is a kind of NP that is common, frequent, and difficult to treat. Tuina, also known as massage and manual therapy, has been used to treat pain in China for thousands of years. It has been clinically proven to be effective in the treatment of pNP caused by cervical spondylosis, lumbar disc herniation, etc. However, its analgesic mechanism is still not clear and has been the focus of research. In this review, we summarize the existing research progress, so as to provide guidance for clinical and basic studies. The analgesic mechanism of tuina is mainly manifested in suppressing peripheral inflammation by regulating the TLR4 pathway and miRNA, modulating ion channels (such as P2X3 and piezo), inhibiting the activation of glial cells, and adjusting the brain functional alterations. Overall, tuina has an analgesic effect by acting on different levels of targets, and it is an effective therapy for the treatment of pNP. It is necessary to continue to study the mechanism of tuina analgesia.

Glutamatergic systems in neuropathic pain and emerging non-opioid therapies

Neuropathic pain, a disease of the somatosensory nervous system, afflicts many individuals and adequate management with current pharmacotherapies remains elusive. The glutamatergic system of neurons, receptors and transporters are intimately involved in pain but, to date, there have been few drugs developed that therapeutically modulate this system. Glutamate transporters, or excitatory amino acid transporters (EAATs), remove excess glutamate around pain transmitting neurons to decrease nociception suggesting that the modulation of glutamate transporters may represent a novel approach to the treatment of pain. This review highlights and summarizes (1) the physiology of the glutamatergic system in neuropathic pain, (2) the preclinical evidence for dysregulation of glutamate transport in animal pain models, and (3) emerging novel therapies that modulate glutamate transporters. Successful drug discovery requires continuous focus on basic and translational methods to fully elucidate the etiologies of this disease to enable the development of targeted therapies. Increasing the efficacy of astrocytic EAATs may serve as a new way to successfully treat those suffering from this devastating disease.

Effect of Physiotherapeutic Interventions on Biomarkers of Neuropathic Pain: A Systematic Review of Preclinical Literature

The purpose of this systematic review was to evaluate the effects of physiotherapeutic interventions on biomarkers of neuropathic pain in preclinical models of peripheral neuropathic pain (PNP). The search was performed in Pubmed, Web of Science, EMBASE, Cochrane, Cinhal, Psycinfo, Scopus, Medline, and Science Direct. Studies evaluating any type of physiotherapy intervention for PNP (systemic or traumatic) were included. Eighty-one articles were included in this review. The most common PNP model was chronic constriction injury, and the most frequently studied biomarkers were related to neuro-immune processes. Exercise therapy and Electro-acupuncture were the 2 most frequently studied physiotherapy interventions while acupuncture and joint mobilization were less frequently examined. Most physiotherapeutic interventions modulated the expression of biomarkers related to neuropathic pain. Whereas the results seem promising; they have to be considered with caution due to the high risk of bias of included studies and high heterogeneity of the type and anatomical localization of biomarkers reported. The review protocol is registered on PROSPERO (CRD42019142878). PERSPECTIVE: This article presents the current evidence about physiotherapeutic interventions on biomarkers of neuropathic pain in preclinical models of peripheral neuropathic pain. Existing findings are reviewed, and relevant data are provided on the effectiveness of each physiotherapeutic modality, as well as its certainty of evidence and clinical applicability.

The distributed nociceptive system: a novel framework for understanding pain

Our current understanding of central nervous system mechanisms supporting the experience of pain remains remarkably limited and produces substantial challenges when seeking to better diagnose and treat chronic pain. A new conceptual framework - The Distributed Nociceptive System - emphasizes system-level aspects of nociceptive processing by incorporating population coding and distributed process. The Distributed Nociceptive System provides a structure for understanding complex spatial aspects of chronic pain and provides a clear rationale for the further development of multi-disciplinary treatments for chronic pain.

The relevance of real-world data for the evaluation of neuropathic pain treatments

Treatment of neuropathic pain (NP) is challenging. Interest in real-world evidence (RWE) for benefit-risk assessments of NP treatments increases given the paucity of drugs showing efficacy in randomized controlled trials and restricted labels of available medicines. To provide further context, a literature review regarding regulatory use of RWE and a clinical trial registry search for randomized controlled trials over the last 10 years was carried out. Taken together, and especially for available NP treatments, there is increasing support to consider RWE when evaluating their benefit-risk profile. Examples are provided in which RWE could be used effectively for updating the product label and informing treatment recommendations. Collected and analyzed according to state-of-the-art standards, RWE can inform treatment recommendations and product label decisions.

Selective activation of Gαob by an adenosine A1 receptor agonist elicits analgesia without cardiorespiratory depression

The development of therapeutic agonists for G protein-coupled receptors (GPCRs) is hampered by the propensity of GPCRs to couple to multiple intracellular signalling pathways. This promiscuous coupling leads to numerous downstream cellular effects, some of which are therapeutically undesirable. This is especially the case for adenosine A1 receptors (A1Rs) whose clinical potential is undermined by the sedation and cardiorespiratory depression caused by conventional agonists. We have discovered that the A1R-selective agonist, benzyloxy-cyclopentyladenosine (BnOCPA), is a potent and powerful analgesic but does not cause sedation, bradycardia, hypotension or respiratory depression. This unprecedented discrimination between native A1Rs arises from BnOCPA's unique and exquisitely selective activation of Gob among the six Gαi/o subtypes, and in the absence of β-arrestin recruitment. BnOCPA thus demonstrates a highly-specific Gα-selective activation of the native A1R, sheds new light on GPCR signalling, and reveals new possibilities for the development of novel therapeutics based on the far-reaching concept of selective Gα agonism.

NRD.E1, an innovative non‐opioid therapy for painful diabetic peripheral neuropathy ‐ a randomised proof of concept study

Background

Painful diabetic peripheral neuropathy (PDPN) affects up to 26% of patients with diabetes mellitus, with major impacts on their general health and well‐being. Most available drugs fail to deliver acceptable pain reduction in the majority of patients and are often poorly tolerated. NRD.E1 is a novel product that has shown anti‐nociceptive preclinical effects and good tolerability in healthy volunteer studies.

Methods

This phase 2a, randomized, dose‐finding, Proof of Concept study enrolled patients with PDPN of ≥3 months duration. After at least one treatment‐free week (WO week), 88 patients entered a 1‐week single‐blind (SB)‐placebo run‐in period, followed by 3 weeks' double‐blind (DB) treatment, during which they received NRD.E1 at 10, 40 or 150 mg/day or placebo.

Results

The primary endpoint (change from SB‐placebo run‐in week to week 3 in weekly mean of daily average numerical rating scale [NRS] pain intensity) showed clinically relevant placebo‐corrected treatment effect pain reductions at 40 mg and 150 mg/day of 0.82 (95% CI: 0.07, 1.58, p = 0.034) and 0.66 (95% CI: −0.03, 1.35; p = 0.061) NRS points, respectively, though did not meet the pre‐specified value of p = 0.016 required due to multiplicity. An additional post hoc endpoint looking at the change from WO baseline to week 3 in weekly mean of daily average NRS showed the placebo‐corrected treatment effect was 1.46 (95% CI: 0.26, 2.66), and 1.20 (95% CI: 0.10, 2.29) NRS points, respectively. Secondary and post hoc analyses of NRS pain data (including 30 & 50% responder rate and NNT), sleep interference, Short‐form McGill pain questionnaire (especially pain intensity assessed on Visual Analogue Scale), Patient's and Clinician's Global Impression of Change showed effects consistent with the primary findings. NRD.E1 was well tolerated, with only headache reported in more than two patients and more frequently on NRD.E1 than placebo.

Conclusions

The data suggest that NRD.E1 potentially represents a novel non‐opioid therapeutic option for patients with PDPN, with at least similar efficacy and better tolerability than available therapies, justifying its further evaluation in larger‐scale confirmatory studies.

Significance

NRD.E1 is a novel non‐opioid therapeutic which is being developed for the treatment of PDPN. In this randomized, controlled, dose‐finding, Proof of Concept study, NRD.E1 induced a clinically relevant pain reduction and it was well tolerated. Available data suggest that NRD.E1 has at least similar efficacy and better tolerability than the currently available therapies, potentially offering a promising new therapeutic option to patients with PDPN and possibly other neuropathic pain indications.

Micro- and nanocarriers for pain alleviation

Acute or chronic pain is a major source of impairment in quality of life and affects a substantial part of the population. To date, pain is alleviated by a limited range of treatments with significant toxicity, increased risk of misuse and inconsistent efficacy, owing, in part, to lack of specificity and/or unfavorable pharmacokinetic properties. Thanks to the unique properties of nanoscaled drug carriers, nanomedicine may enhance drug biodistribution and targeting, thus contributing to improved bioavailability and lower off-target toxicity. After a brief overview of the current situation and the main critical issues regarding pain alleviation, this review will examine the most advanced approaches using nanomedicine of each drug class, from the preclinical stage to approved nanomedicines.

Pharmacological treatments of neuropathic pain: real-life comparisons using propensity score matching

ABSTRACT

Studies comparing different drug treatments for chronic neuropathic pain (NP) are very limited. We, therefore, examined 4 recommended treatments, namely, antidepressants (duloxetine, venlafaxine, and tricyclic antidepressants), antiepileptics (gabapentine and pregabalin), weak opioids, and strong opioids, among patients with NP evaluated before first visit in a tertiary pain treatment centre and 6 months later. Patients with both a clinical diagnosis of NP and a DN4 score ≥3/7 were selected from patients enrolled in the Quebec Pain Registry. Each participant was assigned an inverse weighting of the probability of receiving any NP treatment, taking into account their age, sex, baseline pain intensity, pain duration, pain catastrophizing tendency, education level, employment, and comedications at 6-month follow-up (M6). Patients were considered as improved if they presented at least a 30% reduction on average pain intensity at M6 compared with baseline. A total of 944 patients completed both baseline and M6 evaluations. Overall, 23.0% of patients were significantly improved for pain intensity at M6. There was no significant difference in proportions patients taking or not antidepressants, gabapentinoids, or weak opioids. Among patients taking strong opioids (N = 288), 13.9% (N = 40/288) were improved vs 27.0% (177/656) of those who were not on opioids (P < 0.004). Inverse probability of treatment weighting confirmed that the proportion of patients who improved was significantly lower among those taking strong opioids compared with those who did not (P < 0.001). In conclusion, long-term use of strong opioids is a treatment suited for a limited proportion of patients with chronic NP.

Chronic neuropathic pain is more than a perception: Systems and methods for an integral characterization

The management of chronic neuropathic pain remains a challenge, because pain is subjective, and measuring it objectively is usually out of question. However, neuropathic pain is also a signal provided by maladaptive neuronal activity. Thus, the integral management of chronic neuropathic pain should not only rely on the subjective perception of the patient, but also on objective data that measures the evolution of neuronal activity. We will discuss different objective and subjective methods for the characterization of neuropathic pain. Additionally, the gaps and proposals for an integral management of chronic neuropathic pain will also be discussed. The current management that relies mostly on subjective measures has not been sufficient, therefore, this has hindered advances in pain management and clinical trials. If an integral characterization is achieved, clinical management and stratification for clinical trials could be based on both questionnaires and neuronal activity. Appropriate characterization may lead to an increased effectiveness for new therapies, and a better quality of life for neuropathic pain sufferers.

Update on Interventional Management of Neuropathic Pain: A Delphi Consensus of the Spanish Pain Society Neuropathic Pain Task Force

Background and Objectives: Interventional management of neuropathic pain (NP) is available to the patients who do not obtain satisfactory pain relief with pharmacotherapy. Evidence supporting this is sparse and fragmented. We attempted to summarize and critically appraise the existing data to identify strategies that yield the greatest benefit, guide clinicians, and identify areas that merit further investigation. Material and Methods: A two-round Delphi survey that involved pain clinic specialists with experience in the research and management of NP was done over an ad hoc 26-item questionnaire made by the authors. Consensus on each statement was defined as either at least 80% endorsement or rejection after the 2nd round. Results: Thirty-five and 29 panelists participated in the 1st and 2nd round, respectively. Consensus was reached in 20 out of 26 statements. There is sufficient basis to treat postherpetic neuralgias and complex regional pain syndromes with progressive levels of invasiveness and failed back surgery syndrome with neuromodulation. Radiculopathies and localized NP can be treated with peripheral blocks, neuromodulation, or pulsed radiofrequency. Non-ablative radiofrequency and non-paresthetic neuromodulation are efficacious and better tolerated than ablative and suprathreshold procedures. Conclusions: A graded approach, from least to most invasive interventions has the potential to improve outcomes in many patients with common refractory NP conditions. Preliminary promising data warrant further research on new indications, and technical advances might enhance the safety and efficacy of current and future therapies.

Impact of variability in baseline pain on the placebo response in randomized, placebo-controlled, crossover trials in peripheral neuropathic pain

ABSTRACT

Large placebo responses often negatively affect randomized controlled trials within the pain area. Understanding different possible factors that influence the placebo response is therefore important. In this retrospective analysis, we hypothesized that a large variability in baseline pain score would predict a greater placebo response and analyzed the impact of the coefficient of variation, SD, and difference between the highest and lowest numeric rating scale (NRS) score at baseline on the placebo response. A total of 160 observations on placebo response from 3 controlled clinical trials with a crossover design were included in this study. In general, the placebo response was low with a mean reduction in pain intensity of 0.5 points (range -5 to 7) measured on a 0 to 10 point NRS, and only 15% were placebo responders as defined by more than 30% reduction in NRS pain score from baseline to the end of the placebo treatment period. We found no significant impact of baseline pain coefficient of variation, SD, or the difference between lowest and highest baseline pain score on the placebo response. Placebo response in one trial did not predict placebo response in another trial. A large placebo response was not associated with a large treatment response. In conclusion, in this retrospective data analysis, there was no impact of baseline pain variability on the placebo response in controlled clinical trials with a crossover design in patients with peripheral neuropathic pain.

The Treatment of Painful Diabetic Neuropathy

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.

Bibliometric and visualized analysis of Neuropathic pain based on Web of Science and CiteSpace over the last 20 years

OBJECTIVE

The purpose of this bibliometric analysis was to explore disciplinary hotspots and collaborative networks in research on neuropathic pain (NPP) research in the past 20 years.

METHODS

The articles related to NPP were obtained from Web of Science database. Global publications on neuropathic pain were analyzed in terms of different aspects such as number of papers, citation rates, authors, institutions, countries/regions, journals, and funding, as well as relevant partnerships and topic hotspots RESULTS: From 2001 to 2020, 6905 articles related to NPP research were published worldwide. The number of publications had increased over the last 20 years continually. Pain was the most productive and the most frequently co-cited journal. Baron R was the most productive and influential author. The most productive country and institution were USA and Harvard University respectively. Researchers and institutions from the USA, Japan and China were the core research forces. There was a broad and close cooperation in the field worldwide. The top authors and top institutions had collaborated relatively closely with others.

CONCLUSIONS

The research of NPP is a well-developed and prospective field of medical study. Pain, European Journal of Pain, and Molecular Pain show more interested in this field. The USA, Harvard University, and Ralf Baron were the top country, institution, and author, respectively. Global research collaboration is extensive. Top institutions and authors had cooperation.

Identification of Neuropathic Pain Severity based on Linear and Non-Linear EEG Features

The lack of an integral characterization of chronic neuropathic pain (NP) has led to pharmacotherapy mismanagement and has hindered advances in clinical trials. In this study, we attempted to identify chronic NP by fusing psychometric (based on the Brief Inventory of Pain - BIP), and both linear and non-linear electroencephalographic (EEG) features. For this purpose, 35 chronic NP patients were recruited voluntarily. All the volunteers answered the BIP; and additionally, 22 EEG channels positioned in accordance with the 10/20 international system were registered for 10 minutes at resting state: 5 minutes with eyes open and 5 minutes with eyes closed. EEG Signals were sampled at 250 Hz within a bandwidth between 0.1 and 100 Hz. As linear features, absolute band power was obtained per clinical frequency band: delta (0.1~4 Hz), theta (4~8 Hz), alpha (8~12 Hz), beta (12~30 Hz) and gamma (30~100 Hz); considering five regions: prefrontal, frontal, central, parietal and occipital. As non-linear features, approximate entropy was calculated per channel and per clinical frequency band with addition of the broadband (0.1~100 Hz). Resulting feature vectors were grouped in line with the BIP outcome. Three groups were considered: low, moderate, and high pain. Finally, BIP-EEG patterns were classified in those three classes, achieving 96% accuracy. This result improves a previous work of a SVM classifier that used exclusively linear EEG features and showed an accuracy between 87% and 90% per class to predict central NP after spinal cord injury.