Analgesic mechanisms of gabapentinoids and effects in experimental pain models: a narrative review

Association between gabapentin use and risk of dementia in adults with chronic pain: A nested case-control study

STUDY OBJECTIVE

To explore the association between gabapentin use and the risk of dementia in patients with chronic pain, considering the rising concerns of dementia in an aging population and the potential cognitive impacts of chronic pain management.

DESIGN

A nested case-control study utilizing data from a longitudinal health insurance database.

SETTING

The study is based on a longitudinal health insurance database spanning 2000-2019 in Taiwan.

PATIENTS

A total of 201,492 patients aged 50 years and older diagnosed with chronic pain between 2001 and 2017 were included. The study focused on individuals with chronic pain, excluding those diagnosed with dementia a year before or after their chronic pain diagnosis.

INTERVENTION

Analysis of gabapentin prescription history was conducted, considering the cumulative dose from the chronic pain diagnosis date to the dementia diagnosis date or equivalent period for controls.

MEASUREMENT

Data included demographics, gabapentin prescription history, and comorbidities. Logistic regression was used to estimate odds ratios for dementia risk.

MAIN RESULTS

No significant difference in the risk of dementia was found between low and high cumulative doses of gabapentin. The adjusted odds ratio for dementia risk associated with gabapentin use was 0.91 (95 % C.I. 0.83-1.01), indicating no substantial increase in risk.

CONCLUSION

Long-term Gabapentin therapy for chronic pain is not associated with a differential risk of dementia across dosage levels, irrespective of age or gender. Further study into its potential cognitive impacts is essential.

Distinctive Neurophysiological Signatures of Analgesia after Inflammatory Pain in the ACC of Freely Moving Mice

Preclinical assessments of pain have often relied upon behavioral measurements and anesthetized neurophysiological recordings. Current technologies enabling large-scale neural recordings, however, have the potential to unveil quantifiable pain signals in conscious animals for preclinical studies. Although pain processing is distributed across many brain regions, the anterior cingulate cortex (ACC) is of particular interest in isolating these signals given its suggested role in the affective ("unpleasant") component of pain. Here, we explored the utility of the ACC toward preclinical pain research using head-mounted miniaturized microscopes to record calcium transients in freely moving male mice expressing genetically encoded calcium indicator 6f (GCaMP6f) under the Thy1 promoter. We verified the expression of GCaMP6f in excitatory neurons and found no intrinsic behavioral differences in this model. Using a multimodal stimulation paradigm across naive, pain, and analgesic conditions, we found that while ACC population activity roughly scaled with stimulus intensity, single-cell representations were highly flexible. We found only low-magnitude increases in population activity after complete Freund's adjuvant (CFA) and insufficient evidence for the existence of a robust nociceptive ensemble in the ACC. However, we found a temporal sharpening of response durations and generalized increases in pairwise neural correlations in the presence of the mechanistically distinct analgesics gabapentin or ibuprofen after (but not before) CFA-induced inflammatory pain. This increase was not explainable by changes in locomotion alone. Taken together, these results highlight challenges in isolating distinct pain signals among flexible representations in the ACC but suggest a neurophysiological hallmark of analgesia after pain that generalizes to at least two analgesics.

Gabapentinoids for the treatment of stroke

ABSTRACT

Gabapentinoid drugs (pregabalin and gabapentin) have been successfully used in the treatment of neuropathic pain and in focal seizure prevention. Recent research has demonstrated their potent activities in modulating neurotransmitter release in neuronal tissue, oxidative stress, and inflammation, which matches the mechanism of action via voltage-gated calcium channels. In this review, we briefly elaborate on the medicinal history and ligand-binding sites of gabapentinoids. We systematically summarize the preclinical and clinical research on gabapentinoids in stroke, including ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, seizures after stroke, cortical spreading depolarization after stroke, pain after stroke, and nerve regeneration after stroke. This review also discusses the potential targets of gabapentinoids in stroke; however, the existing results are still uncertain regarding the effect of gabapentinoids on stroke and related diseases. Further preclinical and clinical trials are needed to test the therapeutic potential of gabapentinoids in stroke. Therefore, gabapentinoids have both opportunities and challenges in the treatment of stroke.

The Association of Gabapentin Initiation with Cognitive and Behavioral Changes in Older Adults with Cognitive Impairment: A Retrospective Cohort Study

BACKGROUND

Although gabapentin has been increasingly prescribed to older adults, the relation between gabapentin initiation and longer-term neurocognitive changes is not well understood. Thus, this study aimed to examine the association of gabapentin initiation with cognitive and motor function decline in older adult participants with cognitive impairment.

METHODS

A retrospective cohort study was conducted using the National Alzheimer's Coordinating Center Uniform Data Set (2005-March 2023). Participants with cognitive impairment at the visit of gabapentin initiation (i.e., index visit) were included. Using the incidence density sampling method, up to nine non-users were randomly selected for each initiator. Cognitive decline over 1 year was defined as any increase in Clinical Dementia Rating global score (CDR®GLOB) or a 1-point increase in CDR® sum of boxes (CDR®SB). Functional status decline over 1 year was defined as at least a 3-point increase in the Functional Activities Questionnaire (FAQ) sum or a 0.3-point increase of mean of FAQ. Motoric decline over 1 year was defined as new clinician reports of gait disorder, falls, and slowness. To mitigate confounding and selection bias, joint stabilized inverse probability of treatment weights and censoring weights were used. Analyses compared index with index + 1 and index + 2 visits.

RESULTS

For the study of cognitive and functional status decline, we included 505 initiators (mean age [SD] 78.8 [7.4]; male = 45%) and 4545 non-users (79.2 [7.6]; 50.1%). For the study of motor decline, we included 353 initiators (78.3 [7.2]; 42.8%) and 3177 non-users (78.5 [7.4]; 48.1%). Gabapentin initiation was not statistically associated with decline on CDR®GLOB, CDR®SB, FAQ sum, or mean FAQ at the index + 1 or index + 2 visits. However, gabapentin initiation was significantly associated with increased odds of new falls at the index + 2 visit (odds ratio [95% confidence interval] 2.5 [1.3, 4.6]).

CONCLUSIONS

Over 1 or 2 years of follow-up, gabapentin initiation was not associated with decline in cognitive or functional status but was associated with increased odds of falling among research participants with cognitive impairment.

Foxg1 Modulation of the Prkcd Gene in the Lateral Habenula Mediates Trigeminal Neuralgia-Associated Anxiety-Like Behaviors in Mice

Trigeminal Neuralgia (TN) is a debilitating disorder frequently accompanied by mood complications such as depression and anxiety. The current study sought to elucidate the molecular underpinnings that contribute to the pathogenesis of TN and its associated anxiety. Employing a partial transection of the infraorbital nerve (pT-ION) in a murine model, we successfully induced sustained primary and secondary orofacial allodynia alongside anxiety-like behavioral manifestations. Transcriptome-wide gene microarray analyses revealed a marked upregulation of Foxg1 subsequent to pT-ION. Targeted knockdown of Foxg1, achieved through bilateral microinjection of adeno-associated virus harboring Foxg1-specific shRNA into the lateral habenula (LHb), resulted in a significant attenuation of both orofacial pain and anxiety-like behaviors. Subsequent RNA sequencing implicated Prkcd as a downstream effector gene modulated by Foxg1. Pharmacological inhibition of protein kinase C delta, encoded by Prkcd, within the LHb markedly ameliorated pT-ION-induced symptomatology. The dual luciferase assay revealed that Foxg1 substantially enhances the transcriptional activity of the Prkcd gene. Collectively, these findings indicate that trigeminal nerve injury leads to Foxg1 upregulation in the LHb, which in turn elevates the expression of Prkcd, culminating in the manifestation of orofacial pain and anxiety-like behaviors. This work offers promising therapeutic targets and a conceptual framework for the clinical management of TN and its psychological comorbidities.

Molecular Mechanisms and Therapeutic Potential of Gabapentin with a Focus on Topical Formulations to Treat Ocular Surface Diseases

Gabapentin (GBP) was originally developed as a potential agonist for Gamma-Amino-Butyric-Acid (GABA) receptors, aiming to inhibit the activation of pain-signaling neurons. Contrary to initial expectations, it does not bind to GABA receptors. Instead, it exhibits several distinct pharmacological activities, including: (1) binding to the alpha-2-delta protein subunit of voltage-gated calcium channels in the central nervous system, thereby blocking the excitatory influx of calcium; (2) reducing the expression and phosphorylation of CaMKII via modulation of ERK1/2 phosphorylation; (3) inhibiting glutamate release and interfering with the activation of NMDA receptors; (4) enhancing GABA synthesis; (5) increasing cell-surface expression of δGABA_A receptors, contributing to its antinociceptive, anticonvulsant, and anxiolytic-like effects. Additionally, GBP displays (6) inhibition of NF-kB activation and subsequent production of inflammatory cytokines, and (7) stimulation of the purinergic adenosine A1 receptor, which supports its anti-inflammatory and wound-healing properties. Initially approved for treating seizures and postherpetic neuralgia, GBP is now broadly used for various conditions, including psychiatric disorders, acute and chronic neuropathic pain, and sleep disturbances. Recently, as an eye drop formulation, it has also been explored as a therapeutic option for ocular surface discomfort in conditions such as dry eye, neurotrophic keratitis, corneal ulcers, and neuropathic ocular pain. This review aims to summarize the evidence supporting the molecular effects of GBP, with a special emphasis on its applications in ocular surface diseases.

Evaluation of the effects of pregabalin and dexamethasone coadministration on preemptive multimodal analgesia and anxiety in third molar surgeries: a triple-blind randomized clinical trial

OBJECTIVE

To evaluate the efficacy of pregabalin and dexamethasone coadministration in preemptive analgesia and anxiety control in lower third molar surgery.

MATERIALS AND METHODS

A triple-blind, split-mouth clinical trial conducted with patients divided into two groups: control group, receiving placebo and dexamethasone, and test group, receiving pregabalin and dexamethasone preoperatively. The evaluated variables were pain, measured by the Visual Analog Scale (VAS), anxiety assessed through the State-Trait Anxiety Inventory (STAI) questionnaires, hemodynamic parameters [Blood Pressure (BP), Heart Rate (HR), Oxygen Saturation (SpO2)], and sedation assessed by the Ramsay scale.

RESULTS

A total of 31 patients were included. The test group exhibited a significant reduction in pain at 2,4,6,8,12,16,24, and 48 h after surgery and in the consumption of rescue analgesics. Anxiety, evaluated by STAI and VAS, showed a significant decrease in the test group (p < 0.001). Additionally, there was a significant decrease in BP at most of the assessed time points (p < 0.05) and a significant reduction in HR at two different time intervals (p = 0.003 and p = 0.009), indicating a positive effect in the test group. There was no significant difference in SpO2 between the groups. Sedation assessment revealed a significant difference at all time points favoring the test group (p < 0.05). There were no significant postoperative adverse effects.

CONCLUSIONS

Pregabalin coadministered with dexamethasone demonstrated significant efficacy in controlling postoperative pain and anxiety, as well as a sedative effect.

CLINICAL RELEVANCE

The coadministration of pregabalin with dexamethasone may presents potential advantages in both pain modulation and psychological well-being of individuals undergoing third molar surgeries.

TRIAL REGISTRATION

Brazilian Clinical Trials Registry (REBEC), No. RBR-378h6t6.

Antinociceptive effect of LMH-2, a new sigma-1 receptor antagonist analog of haloperidol, on the neuropathic pain of diabetic mice

This study evaluates the antiallodynic and antihyperalgesic effects of LMH-2, a new haloperidol (HAL) analog that acts as sigma-1 receptor (σ1 R) antagonist, in diabetic mice using a model of neuropathic pain induced by chronic hyperglycemia. Additionally, we compared its effects with those of HAL. Hyperglycemia was induced in mice by nicotinamide-streptozotocin administration (NA-STZ, 50-130 mg/kg). Four weeks later, mechanical allodynia was assessed using the up-down method, and hyperalgesia was evoked with formalin 0.5%. We evaluated antiallodynic and antihyperalgesic effects of LMH-2 (5.6-56.2 mg/kg), HAL (0.018-0.18 mg/kg) and gabapentin (GBP, 5.6-56.2 mg/kg). The results showed that LMH-2 had a more significant antiallodynic effect compared to HAL and GBP (90.4±8.7 vs 75.1±3.1 and 41.9±2.3%, respectively; P<0.05), as well as an antihyperalgesic effect (96.3±1.2 vs 86.9±7.41 and 86.9±4.8%, respectively; P<0.05). Moreover, the antiallodynic and antihyperalgesic effect of both LMH-2 and HAL were completely abolished by PRE-084 (σ1 R agonist); and partially by pramipexole (a D2-like receptor agonist). Finally, the effect of all treatments on the rotarod test, barra, open field and exploratory behaviors showed that LMH-2 did not alter the animals' balance or the exploratory behavior, unlike as HAL or GBP. The molecular docking included indicate that LMH-2 has lower affinity to the D2R than HAL. These results provide evidence that LMH-2 exerts its antinociceptive effects as a σ1 R antagonist without the adverse effects induced by HAL or GBP. Consequently, LMH-2 can be considered a good and safe strategy for treating neuropathic pain caused by hyperglycemia in patients with diabetes.

Preoperative pregabalin prevents succinylcholine-induced fasciculation and myalgia: A meta-analysis of randomized trials

Succinylcholine is the gold standard neuromuscular blocker for rapid sequence induction; however, its use is associated with fasciculation and myalgia. We performed a systematic review and meta-analysis of randomized controlled clinical trials comparing gabapentinoids versus placebo for the prevention of fasciculations and succinylcholine-induced myalgias. Six randomized clinical studies were included with a total of 481 patients - 241 in the intervention group and 240 in the placebo group. Gabapentinoids reduced the incidence of succinylcholine-induced myalgia (RR=0.69, 95% CI 0.56-0.84, P<.001), which remained statistically significant for pregabalin (RR=0.71, 95% CI 0.54-0.93, P=.013) and gabapentin (RR=0.61, 95% CI 0.45-0.82, P=.001) separately. There was no difference in fasciculations between the groups (RR=0.92, 95% CI 0.82-1.03, P=.148). Preoperative use of gabapentinoids is associated with lower incidence of succinylcholine-induced myalgias within the first 24h of surgery.

Expert Consensus on Ion Channel Drugs for Chronic Pain Treatment in China

Ion channel drugs have been increasing used for chronic pain management with progress in the development of selective calcium channel modulators. Although ion channel drugs have been proven safe and effective in clinical practice, uncertainty remains regarding its use to treat chronic pain. To standardize the clinical practice of ion channel drug for the treatment of chronic pain, the National Health Commission Capacity Building and Continuing Education Center for Pain Diagnosis and Treatment Special Ability Training Project established an expert group to form an expert consensus on the use of ion channel drugs for the treatment of chronic pain after repeated discussions on existing medical evidence combined with the well clinical experience of experts. The consensus provided information on the mechanism of action of ion channel drugs and their recommendations, caution use, contraindications, and precautions for their use in special populations to support doctors in their clinical decision-making.

A comprehensive update on the ADMET considerations for α2δ calcium channel ligand medications for treating restless legs syndrome

INTRODUCTION

Restless legs syndrome/Willis-Ekbom disease (RLS/WED) is a sleep-related sensory-motor disorder associated with poor sleep quality and impaired daily functioning. In patients affected by chronic RLS/WED, a pharmacological therapy is recommended. International guidelines suggest to start the treatment with a α2δ calcium channel ligand in most cases, unless contraindicated.

AREAS COVERED

The present review is based on an extensive Internet and PubMed search from 1986 to 2024. Our purpose is to describe the absorption, distribution, metabolism, and toxicology (ADMET) of the α2δ ligands, with common consideration for the therapeutic class, specificities of different compounds, efficacy, and safety in relation to other treatment options.

EXPERT OPINION

α2δ ligands are quite similar in their ADMET profiles, sharing most of the pharmacokinetics and potential adverse effects. However, we highlight the linear kinetic of gabapentin enacarbil and pregabalin, differently from gabapentin. α2δ ligands are safe and effective for the treatment of RLS/WED. Additional benefits can be obtained in comorbid insomnia, chronic pain syndromes, history of impulse control disorder, and comorbid anxiety. The use of α2δ ligands is associated with poor risk of augmentation. We still need new long-term safe and effective treatments, which could be developed along with our knowledge of RLS/WED pathophysiology.

Pain Science in Practice (Part 7): How Is Descending Modulation of Pain Measured?

SYNOPSIS: Understanding the descending pain modulatory system allows for a neuroscientific explanation of naturally occurring pain relief. Evidence from basic science and clinical studies on the effectiveness of drugs in certain patient groups led to pharmacological manipulation of the descending pain modulatory system for analgesia. Understanding mechanisms and theories helps clinicians make sense of chronic musculoskeletal pain. This editorial explains how test paradigms, including conditioned pain modulation, offset analgesia, and stress-induced analgesia work, provide an overview of a placebo analgesia circuitry, and discusses how evoking activity in the descending pain modulatory system using specific paradigms can give new insights into how specific treatments work to reduce pain. J Orthop Sports Phys Ther 2024;54(2):1-6. doi:10.2519/jospt.2024.12113.

Effects of Gabapentin on Postoperative Pain and Opioid Consumption Following Laparoscopic Cholecystectomy: A Systematic Review and Meta-analysis

PURPOSE

Examine the efficacy of gabapentin on postoperative pain scores and opioid consumption in laparoscopic cholecystectomy.

DESIGN

Systematic review and meta-analysis.

METHODS

PubMed, EBSCO, CINAHL, the Cochrane Central Register of Controlled Trials, Google Scholar, and gray literature was used to search the literature. Only randomized controlled trials were included. Outcomes were reported using the risk ratio and mean difference (MD). Risk of bias and the grades of recommendation, assessment, development, and evaluation (GRADE) system was used to the assessed quality of evidence.

FINDINGS

Nineteen trials involving 2,068 patients were analyzed. Compared to placebo, gabapentin reduced the cumulative pain scores in the first 24 hours after surgery (MD, -1.19; 95% CI, -1.39-0.99; P < .00011), opioid consumption (MD, -3.51; 95% CI, -4.67 to -2.35; P < .00001), and the incidence of postoperative nausea and vomiting (risk ratio, 0.64; 95% CI, 0.52-0.78; P < .00001) with prolonged time to first analgesic rescue (MD, 210.9; 95% CI, 76.90-344.91; P = .002). However, gabapentin has little to no effect on the incidence of sedation, somnolence, and respiratory depression.

CONCLUSIONS

Gabapentin can be added as part of the multimodal pain management for patients undergoing laparoscopic cholecystectomy. Extrapolation of these findings to clinical settings must take into consideration the limitations identified in this review.

Curcuma latifolia Roscoe extract reverses inflammatory pain in mice and offers a favorable CNS safety profile

ETHNOPHARMACOLOGICAL RELEVANCE

Curcuma latifolia Roscoe, a plant in the Curcuma genus, has been used as a food additive and folk medicine in Thailand to treat pelvic pain and improve premenstrual syndrome. Although it has been used for centuries, no scientific studies have proved its potential effects on inflammatory pain and central nervous system (CNS) safety profiles.

AIM OF THE STUDY

This study aimed to evaluate the potential effects of the ethanolic extract of C. latifolia rhizome on inflammatory pain in mice, together with its CNS safety profiles.

MATERIALS AND METHODS

First, network pharmacology was employed to identify the role of bioactive constituents in C. latifolia on inflammatory pain. In addition, in vitro pharmacology was also evaluated to confirm the anti-inflammatory activity of C. latifolia extract at cellular levels in activated macrophages and microglia. Furthermore, the efficacy of the plant extract in attenuating formalin-induced pain-like behaviors in mice was evaluated. Mice were orally administered the extract (125, 250, 500 mg/kg) followed by the measurement of formalin-induced pain-like behaviors. The LABORAS automated behavioral analysis and rotarod test were used to assess potential CNS side effects of C. latifolia extract (500 mg/kg) in mice.

RESULTS

The results demonstrated that major bioactive constituents present in C. latifolia have the ability to regulate multiple targets, biological processes and pathways associated with inflammatory pain as assessed by network pharmacology. C. latifolia modulated peripheral and central immune cells via reducing proinflammatory mediators (NO, TNF-α, and IL-6). C. latifolia extract improved formalin-induced pain-like behaviors in a dose-dependent manner during phase II of the formalin test. The efficacy of the plant extract at doses of 250 and 500 mg/kg was comparable to that of the positive control (indomethacin 10 mg/kg). Furthermore, the highest therapeutic dose of the extract did not affect motor coordination, exploratory behaviors, general behaviors, and overall well-being of mice, indicating no development of potential CNS adverse effects after administration of the extract.

CONCLUSION

These findings provide novel perspectives on using C. latifolia extract for pain management, considering its therapeutic efficacy and CNS safety.

Can gabapentinoids decrease perioperative opioid requirements in orthopaedic trauma patients? A single-centre retrospective analysis

INTRODUCTION

Perioperative pain control in patients with orthopaedic trauma/extremity fractures has gained a lot of attraction from the scientific community in the last two decades. In addition to multimodal analgesia, the use of non-opioid drugs like gabapentinoids for pain relief is gradually finding its place in several orthopaedic subspecialties like spinal surgery, arthroplasty, and arthroscopic procedures. We envisage investigating the effectiveness of gabapentin in perioperative pain control in patients with extremity fractures undergoing surgical fixation.

METHODOLOGY

This was a retrospective comparative study conducted between January 2020 and January 2022. Patients with isolated fractures of the extremity involving long bones who were treated at our trauma centre, during the study period were divided into two groups based on the analgesics they received. Patients who received gabapentin and paracetamol were placed in group GP and those who received only paracetamol were assigned group NGP. Gabapentin was given in a single dose of 300 mg 4 h before surgery. Postoperatively, they were given 300 mg 12 hourly for 2 days. All patients in our trauma centre are usually managed with parenteral paracetamol administration pre and postoperatively. VAS score was calculated postoperatively at 2, 6, 12, 24 and 48 h. Patients requiring additional analgesics for pain relief were administered intravenous tramadol or a buprenorphine patch was applied. Patients in both groups were compared in terms of pain control, the additional requirement of opioid analgesics, and any adverse event related to medications.

RESULTS

One hundred and nineteen patients were enrolled in the study. Out of 65 patients in the NGP group (non-gabapentin group), 74% of patients received additional opioid analgesics apart from paracetamol. Out of the 54 patients in the GP group (gabapentin group), only 41% required additional opioid analgesia for pain control. There was a significant difference in opioid consumption between the two groups (p < 0.01). VAS scores were not significantly different between the two groups at 2, 4, 6, 12, 24 and 48 h. Gender and fracture morphology did not affect opioid intake in the GP group. However, in the non-gabapentin group, there was a significant difference in opioid requirement in patients with intraarticular fractures (p < 0.01).

CONCLUSION

Analgesic requirements vary from patient to patient depending on the injury's severity and surgery duration. However, there are no strict guidelines for pain relief in limb trauma surgeries which often leads to overuse and opioid-related complications or underuse and chronic pain. Gabapentinoids can supplement the analgesic effect of paracetamol in trauma patients during the perioperative period, decreasing the need for opioids.

Novel Targets and Drug Delivery System in the Treatment of Postoperative Pain: Recent Studies and Clinical Advancement

Pain is generated by a small number of peripheral targets. These can be made more sensitive by inflammatory mediators. The number of opioids prescribed to the patients can be reduced dramatically with better pain management. Any therapy that safely and reliably provides extended analgesia and is flexible enough to facilitate a diverse array of release profiles would be useful for improving patient comfort, quality of care, and compliance after surgical procedures. Comparisons are made between new and traditional methods, and the current state of development has been discussed; taking into account the availability of molecular and cellular level data, preclinical and clinical data, and early post-market data. There are a number of benefits associated with the use of nanotechnology in the delivery of analgesics to specific areas of the body. Nanoparticles are able to transport drugs to inaccessible bodily areas because of their small molecular size. This review focuses on targets that act specifically or primarily on sensory neurons, as well as inflammatory mediators that have been shown to have an analgesic effect as a side effect of their anti- inflammatory properties. New, regulated post-operative pain management devices that use existing polymeric systems were presented in this article, along with the areas for potential development. Analgesic treatments, both pharmacological and non-pharmacological, have also been discussed.

Safety and Efficacy of Gabapentin for Pain in Pediatric Patients: A Systematic Review

CONTEXT

Gabapentin has shown benefits for a variety of pain etiologies in adult patients, with off-label use as an adjunctive agent in pediatric patients occurring more frequently.

OBJECTIVES

To summarize the studies which evaluate safety and efficacy of gabapentin for the treatment of pediatric pain.

DATA SOURCES

A systematic review of the literature was conducted via PubMed query with controlled vocabulary and key terms using indexed medical subject heading.

STUDY SELECTION

Prospective studies published between January 1, 2000, and July 1, 2023, were selected utilizing a predetermined exclusion criteria independently by 2 authors, with a third independent author available for discrepancies.

DATA EXTRACTION

Data extraction was performed by 2 authors independently to include study design, patient population and characteristics, drug dosing, and outcomes. Studies were then assessed for their independent risk of bias utilizing the Grading of Recommendations, Assessment, Development, and Evaluations approach to risk of bias.

RESULTS

A total of 11 studies describing 195 pediatric patients who received gabapentin were included. Of the 11 studies, 9 were randomized controlled trials, 1 was a prospective multicenter study, and 1 was an open-label pilot study.

CONCLUSIONS

Heterogeneity of pain type and gabapentin dosing regimens within the included studies made conclusions difficult to quantify. Efficacy likely depends significantly on etiology of pain; however, per these studies, gabapentin is likely safe to use for a variety of pediatric patient populations as a multimodal agent.

Gabapentin and postoperative pain and opioid consumption: A double-blind randomized controlled trial of perioperative pain management for sinus surgery

BACKGROUND

The link between post-operative narcotic prescription and opioid misuse has spurred a nationwide effort to reduce perioperative opioid use. Previous work has suggested that perioperative gabapentin may reduce post-operative pain and opioid consumption across different procedures, although the optimal regimen remains to be defined.

METHODS

Chronic rhinosinusitis (CRS) patients undergoing functional endoscopic sinus surgery (FESS) with or without septoplasty were randomized to receive a 7-day pre- and post-operative course of placebo or gabapentin, starting at 300 mg daily and titrated to 300 mg three times daily, in a double-blind fashion. Primary endpoint was pain level using a validated visual analog scale (VAS). Secondary endpoints included post-operative opioid consumption and side effects, as well as modified Lund-Kennedy endoscopy, Lund-Mackay, and SNOT-22 scores.

RESULTS

Analysis of 35 patients (20 gabapentin, 15 control) showed no significant difference in mean postoperative VAS (p = 0.18) or postoperative opioid consumption between the placebo and gabapentin groups (2.3 and 4.8 oxycodone tablets respectively, p = 0.18). 15 of 35 patients did not require any post-operative oxycodone tablets, and only two patients required more than six tablets.

CONCLUSION

Preliminary results show no significant change in pain after FESS with or without septoplasty in patients taking 7-day pre- and post-operative gabapentin versus placebo. Results also showed no significant difference in opioid consumption between the treatment and placebo groups. Post-operative pain scores and opioid requirements are both quite low following FESS. Many patients do not need opioids at all, suggesting that routine initial post-operative opioid prescriptions can be limited accordingly.

Involvement of microglia in chronic neuropathic pain associated with spinal cord injury - a systematic review

In recent decade microglia have been found to have a central role in the development of chronic neuropathic pain after injury to the peripheral nervous system. It is widely accepted that peripheral nerve injury triggers microglial activation in the spinal cord, which contributes to heightened pain sensation and eventually chronic pain states. The contribution of microglia to chronic pain arising after injury to the central nervous system, such as spinal cord injury (SCI), has been less studied, but there is evidence supporting microglial contribution to central neuropathic pain. In this systematic review, we focused on post-SCI microglial activation and how it is linked to emergence and maintenance of chronic neuropathic pain arising after SCI. We found that the number of studies using animal SCI models addressing microglial activity is still small, compared with the ones using peripheral nerve injury models. We have collected 20 studies for full inclusion in this review. Many mechanisms and cellular interactions are yet to be fully understood, although several studies report an increase of density and activity of microglia in the spinal cord, both in the vicinity of the injury and in the spared spinal tissue, as well as in the brain. Changes in microglial activity come with several molecular changes, including expression of receptors and activation of signalling pathways. As with peripheral neuropathic pain, microglia seem to be important players and might become a therapeutic target in the future.

Effects of Acute and Chronic Gabapentin Treatment on Cardiovascular Function of Rats

Gabapentin (GBP), a GABA analogue, is primarily used as an anticonvulsant for the treatment of partial seizures and neuropathic pain. Whereas a majority of the side effects are associated with the nervous system, emerging evidence suggests there is a high risk of heart diseases in patients taking GBP. In the present study, we first used a preclinical model of rats to investigate, firstly, the acute cardiovascular responses to GBP (bolus i.v. injection, 50 mg/kg) and secondly the effects of chronic GBP treatment (i.p. 100 mg/kg/day × 7 days) on cardiovascular function and the myocardial proteome. Under isoflurane anesthesia, rat blood pressure (BP), heart rate (HR), and left ventricular (LV) hemodynamics were measured using Millar pressure transducers. The LV myocardium and brain cortex were analyzed by proteomics, bioinformatics, and western blot to explore the molecular mechanisms underlying GBP-induced cardiac dysfunction. In the first experiment, we found that i.v. GBP significantly decreased BP, HR, maximal LV pressure, and maximal and minimal dP/dt, whereas it increased IRP-AdP/dt, Tau, systolic, diastolic, and cycle durations (* p < 0.05 and ** p < 0.01 vs. baseline; n = 4). In the second experiment, we found that chronic GBP treatment resulted in hypotension, bradycardia, and LV systolic dysfunction, with no change in plasma norepinephrine. In the myocardium, we identified 109 differentially expressed proteins involved in calcium pathways, cholesterol metabolism, and galactose metabolism. Notably, we found that calmodulin, a key protein of intracellular calcium signaling, was significantly upregulated by GBP in the heart but not in the brain. In summary, we found that acute and chronic GBP treatments suppressed cardiovascular function in rats, which is attributed to abnormal calcium signaling in cardiomyocytes. These data reveal a novel side effect of GBP independent of the nervous system, providing important translational evidence to suggest that GBP can evoke adverse cardiovascular events by depression of myocardial function.

Precision, integrative medicine for pain management in sickle cell disease

Sickle cell disease (SCD) is a prevalent and complex inherited pain disorder that can manifest as acute vaso-occlusive crises (VOC) and/or chronic pain. Despite their known risks, opioids are often prescribed routinely and indiscriminately in managing SCD pain, because it is so often severe and debilitating. Integrative medicine strategies, particularly non-opioid therapies, hold promise in safe and effective management of SCD pain. However, the lack of evidence-based methods for managing SCD pain hinders the widespread implementation of non-opioid therapies. In this review, we acknowledge that implementing personalized pain treatment strategies in SCD, which is a guideline-recommended strategy, is currently fraught with limitations. The full implementation of pharmacological and biobehavioral pain approaches targeting mechanistic pain pathways faces challenges due to limited knowledge and limited financial and personnel support. We recommend personalized medicine, pharmacogenomics, and integrative medicine as aspirational strategies for improving pain care in SCD. As an organizing model that is a comprehensive framework for classifying pain subphenotypes and mechanisms in SCD, and for guiding selection of specific strategies, we present evidence updating pain research pioneer Richard Melzack's neuromatrix theory of pain. We advocate for using the updated neuromatrix model to subphenotype individuals with SCD, to better select personalized multimodal treatment strategies, and to identify research gaps fruitful for exploration. We present a fairly complete list of currently used pharmacologic and non-pharmacologic SCD pain therapies, classified by their mechanism of action and by their hypothesized targets in the updated neuromatrix model.

Pharmacological and Nonpharmacological Treatments for Painful Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most prevalent chronic complications of diabetes. The lifetime prevalence of DPN is thought to be >50%, and 15%-25% of patients with diabetes experience neuropathic pain, referred to as "painful DPN." Appropriate treatment of painful DPN is important because this pain contributes to a poor quality of life by causing sleep disturbance, anxiety, and depression. The basic principle for the management of painful DPN is to control hyperglycemia and other modifiable risk factors, but these may be insufficient for preventing or improving DPN. Because there is no promising diseasemodifying medication for DPN, the pain itself needs to be managed when treating painful DPN. Drugs for neuropathic pain, such as gabapentinoids, serotonin-norepinephrine reuptake inhibitors, tricyclic antidepressants, alpha-lipoic acid, sodium channel blockers, and topical capsaicin, are used for the management of painful DPN. The U.S. Food and Drug Administration (FDA) has approved pregabalin, duloxetine, tapentadol, and the 8% capsaicin patch as drugs for the treatment of painful DPN. Recently, spinal cord stimulation using electrical stimulation is approved by the FDA for the treatment for painful DPN. This review describes the currently available pharmacological and nonpharmacological treatments for painful DPN.

The Preoperative Use of Gabapentinoids for the Treatment of Acute Postoperative Pain Following Lumbar Spine Fixation Surgery

BACKGROUND

Postoperative pain following posterior fixation is caused not only by tissue injury during surgery and is related to inflammatory, neuropathic, and visceral pain. This study aims to answer the question, "Is there a role for gabapentinoids in reducing postoperative pain?" In addition, it demonstrates which gabapentinoids may be used, for how long, and at what dose.

METHODS

The study was planned as a prospective, randomized, double-blind study. Lumbar posterior fixation was included and patients were divided into 9 groups. Gabapentinoids and a placebo were administered. Postoperative pain at hours 1, 6, 12, and 24 was evaluated by visual analog scale (VAS).

RESULTS

This study included 252 patients (141 women, 111 men). The median age was 51.62 years. A statistically significant difference was found when VAS-1, VAS-6, VAS-12, and VAS-24 scores were compared between all groups (P ˂ 0.001). Single and low doses of gabapentinoids were found to be ineffective (P > 0.05). Long-term and high-dose gabapentinoids had complications (P ˂ 0.001). Single and high doses of gabapentinoids were effective and safe (P ˂ 0.001).

CONCLUSIONS

Postoperative use of gabapentin for controlling early and late-stage pain is safe and effective. Single and high-dose gabapentin was the first choice. A single and high dose of pregabalin is the second choice.

Mapping the neuroethological signatures of pain, analgesia, and recovery in mice

Ongoing pain is driven by the activation and modulation of pain-sensing neurons, affecting physiology, motor function, and motivation to engage in certain behaviors. The complexity of the pain state has evaded a comprehensive definition, especially in non-verbal animals. Here, in mice, we used site-specific electrophysiology to define key time points corresponding to peripheral sensitivity in acute paw inflammation and chronic knee pain models. Using supervised and unsupervised machine learning tools, we uncovered sensory-evoked coping postures unique to each model. Through 3D pose analytics, we identified movement sequences that robustly represent different pain states and found that commonly used analgesics do not return an animal's behavior to a pre-injury state. Instead, these analgesics induce a novel set of spontaneous behaviors that are maintained even after resolution of evoked pain behaviors. Together, these findings reveal previously unidentified neuroethological signatures of pain and analgesia at heightened pain states and during recovery.

Pregabalin-Tolperisone Combination to Treat Neuropathic Pain: Improved Analgesia and Reduced Side Effects in Rats

The current treatment of neuropathic pain (NP) is unsatisfactory; therefore, effective novel agents or combination-based analgesic therapies are needed. Herein, oral tolperisone, pregabalin, and duloxetine were tested for their antinociceptive effect against rat partial sciatic nerve ligation (pSNL)-induced tactile allodynia described by a decrease in the paw withdrawal threshold (PWT) measured by a dynamic plantar aesthesiometer. On day 7 after the operation, PWTs were assessed at 60, 120, and 180 min post-treatment. Chronic treatment was continued for 2 weeks, and again, PWTs were measured on day 14 and 21. None of the test compounds produced an acute antiallodynic effect. In contrast, after chronic treatment, tolperisone and pregabalin alleviated allodynia. In other experiments, on day 14, the acute antiallodynic effect of the tolperisone/pregabalin or duloxetine combination was measured. As a novel finding, a single dose of the tolperisone/pregabalin combination could remarkably alleviate allodynia acutely. It also restored the neuropathy-induced elevated CSF glutamate content. Furthermore, the combination is devoid of adverse effects related to motor and gastrointestinal transit functions. Tolperisone and pregabalin target voltage-gated sodium and calcium channels, respectively. The dual blockade effect of the combination might explain its advantageous acute analgesic effect in the present work.

Evaluation of Pre-emptive Analgesia in Total Knee Arthroplasty During Early Post-operative Periods

INTRODUCTION

Pre-emptive analgesia is expected to decrease post-operative pain. The degree of soft tissue release is directly related to preoperative deformity; we presume the severity of pain has a similar correlation in patients undergoing total knee arthroplasty (TKA). The main purpose of this research was to evaluate the effects of pre-emptive analgesia of different drugs in TKA with different degrees of preoperative genu varus.

METHODS

In this prospective observational study, 67 patients were enrolled with different degrees of genu varus deformity. They were subdivided into two groups: those with ≥15° and those with <15° varus deformities of the knee. Etoricoxib 60 mg and pregabalin 75 mg were administered orally in all the patients as pre-emptive analgesia two hours before surgery. Parameters such as the amount of soft tissue release, visual analog score (VAS), knee range of motion, complications, etc. were documented from the pre-operative period to 72 hours post-TKA.

RESULTS

With pre-emptive analgesia in post-TKA patients, the VAS score demonstrated a statistically significant difference at 24, 48, and 72 hours. The comparison of intraoperative flexion between <15° and ≥15° showed a statistically significant difference with pre-emptive analgesia in post-TKA patients.

CONCLUSION

The use of etoricoxib 60 mg and pregabalin 75 mg, two hours before surgery reduced the pain scores in patients undergoing TKA with different degrees of genu varus and correlated with intraoperative parameters associated with soft medial tissue release for genu varus.

Pregabalin can interact synergistically with Kv7 channel openers to exert antinociception in mice

Chronic pain is a common public health problem and remains an unmet medical need. Currently available analgesics usually have limited efficacy for the treatment of chronic pain, including neuropathic pain and persistent inflammatory pain, or they are accompanied by many adverse side effects. The voltage-gated calcium channel blocker (pregabalin) and potassium channel openers (flupirtine and retigabine) have been widely used for the management of chronic pain, but their effectiveness in combination is unclear. In this research, we evaluated the antinociceptive effects of pregabalin in combination with flupirtine or retigabine in carrageenan-induced inflammatory pain and paclitaxel-induced peripheral neuropathy in mice using the von Frey test. Isobolographic analysis indicated that pregabalin exerted synergistic antinociceptive effects when combined with flupirtine or retigabine in neuropathic and inflammatory pain models. Furthermore, the antinociceptive effects of pregabalin, flupirtine/retigabine, and their combinations were significantly attenuated by the Kv7 channel blocker XE991. The favored dose ratio between pregabalin and flupirtine/retigabine in combinations was also investigated. Finally, we evaluated the motor coordination of their combinations using the rotarod test, and the outcomes underpinned their safety. Collectively, our results support the potential use of pregabalin in combination with flupirtine or retigabine to alleviate chronic pain.

Sleep as a Therapeutic Target for Pain Management

PURPOSE OF REVIEW

The purpose of this review is to provide a summary of the utilization of sleep as a therapeutic target for chronic pain and to evaluate the recent literature on current and proposed pharmacologic and non-pharmacologic sleep interventions used in the management of pain disorders.

RECENT FINDINGS

Sleep is a promising therapeutic target in the treatment of pain disorders with both non-pharmacologic and pharmacologic therapies. Non-pharmacologic therapies include cognitive behavioral therapy and sensory-based therapies such as pink noise, audio-visual stimulation, and morning bright light therapy. Pharmacologic therapies include melatonin, z-drugs, gabapentinoids, and the novel orexin antagonists. However, more research is needed to clarify if these therapies can improve pain specifically by improving sleep. There is a vast array of investigational opportunities in sleep-targeted therapies for pathologic pain, and larger controlled, prospective trials are needed to fully elucidate their efficacy.

Efficacy and Safety of Gabapentin on Postoperative Pain Management After Bariatric Surgery: A Systematic Review and Meta-Analysis

PURPOSE

Examine the efficacy and safety of perioperative gabapentin in bariatric surgical patients.

DESIGN

Systematic Review and Meta-analysis.

METHODS

An exhaustive search was conducted using PubMed, Cochrane Library, MEDLINE, CINAHL, Google Scholar, and other gray literature. Only randomized controlled trials evaluating the use of gabapentin in bariatric surgery were included. Risk ratio (RR) and mean difference (MD) were used to estimate outcomes with suitable effect models. Quality of evidence was assessed using the Risk of Bias and GRADE system.

FINDINGS

Four trials consisting of 283 patients were analyzed. The use of gabapentin significantly lowered the cumulative pain score in the first 24 hours after surgery by an average of 1.04 (MD, -1.04; 95% CI, -1.45 to -0.63; P < .00001). Gabapentin also reduced the overall morphine equivalent consumption by 7.89 mg (MD, -7.89; 95% CI, -13.56 to -2.2; P = .006). However, gabapentin did not affect the incidence of PONV (RR, 0.61; 95% CI, 0.38-1.00; P = .05), somnolence (RR, 1.25; 95% CI, 0.57-2.73; P = .57), dizziness (RR, 1.01; 95% CI, 0.40-2.54; P = .99), and headache (RR, 0.76; 95% CI, 0.25-2.30; P = .62). Substantial heterogeneity, imprecision of the effect size, and potential publication bias were limitations of this review.

CONCLUSIONS

The use of gabapentin is effective in the management of postoperative pain in bariatric surgery. However, there is limited data regarding the opioid-sparing effect and adverse effect profiles of gabapentin in the bariatric surgical population.

L-type Amino Acid Transporter 1 (SLC7A5)-Mediated Transport of Pregabalin at the Rat Blood-Spinal Cord Barrier and its Sensitivity to Plasma Branched-Chain Amino Acids

Pregabalin is an anti-neuropathic pain drug inhibiting the α2δ subunit of the voltage-dependent calcium channel in the spinal cord. The aim of this study is to characterize the transport mechanism of pregabalin at the blood-spinal cord barrier (BSCB) by means of in vivo experiments in rats and in vitro studies using primary-cultured rat spinal cord endothelial cells. We isolated endothelial cells by culturing rat spinal cord tissue in the presence of puromycin, and confirmed the expression of BSCB markers such as Cd31, Mdr1a, and Claudin-5. The uptake of pregabalin by primary-cultured rat spinal cord endothelial cells was sodium-independent and was significantly inhibited by L-leucine, 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid, and JPH203. These results suggest the involvement of L-type amino acid transporter (LAT) 1. LAT1 mRNA and protein was expressed in primary-cultured rat spinal cord endothelial cells, which is consistent with LAT1 expression at the BSCB. In the in vivo study, the transfer of pregabalin to rat spinal cord and brain was significantly decreased by the pre-administration of branched chain amino acids (BCAAs), which are endogenous substrates of LAT1. Our results indicate that pregabalin transport across the BSCB is mediated at least in part by LAT1 and is inhibited by plasma BCAAs.

Pregabalin Silences Oxaliplatin-Activated Sensory Neurons to Relieve Cold Allodynia

Oxaliplatin is a platinum-based chemotherapeutic agent that causes cold and mechanical allodynia in up to 90% of patients. Silent Nav1.8-positive nociceptive cold sensors have been shown to be unmasked by oxaliplatin, and this event has been causally linked to the development of cold allodynia. We examined the effects of pregabalin on oxaliplatin-evoked unmasking of cold sensitive neurons using mice expressing GCaMP-3 in all sensory neurons. Intravenous injection of pregabalin significantly ameliorates cold allodynia, while decreasing the number of cold sensitive neurons by altering their excitability and temperature thresholds. The silenced neurons are predominantly medium/large mechano-cold sensitive neurons, corresponding to the "silent" cold sensors activated during neuropathy. Deletion of α2δ1 subunits abolished the effects of pregabalin on both cold allodynia and the silencing of sensory neurons. Thus, these results define a novel, peripheral inhibitory effect of pregabalin on the excitability of "silent" cold-sensing neurons in a model of oxaliplatin-dependent cold allodynia.

Integrating mechanistic-based and classification-based concepts into perioperative pain management: an educational guide for acute pain physicians

Chronic pain begins with acute pain. Physicians tend to classify pain by duration (acute vs chronic) and mechanism (nociceptive, neuropathic and nociplastic). Although this taxonomy may facilitate diagnosis and documentation, such categories are to some degree arbitrary constructs, with significant overlap in terms of mechanisms and treatments. In clinical practice, there are myriad different definitions for chronic pain and a substantial portion of chronic pain involves mixed phenotypes. Classification of pain based on acuity and mechanisms informs management at all levels and constitutes a critical part of guidelines and treatment for chronic pain care. Yet specialty care is often siloed, with advances in understanding lagging years behind in some areas in which these developments should be at the forefront of clinical practice. For example, in perioperative pain management, enhanced recovery protocols are not standardized and tend to drive treatment without consideration of mechanisms, which in many cases may be incongruent with personalized medicine and mechanism-based treatment. In this educational document, we discuss mechanisms and classification of pain as it pertains to commonly performed surgical procedures. Our goal is to provide a clinical reference for the acute pain physician to facilitate pain management decision-making (both diagnosis and therapy) in the perioperative period.

The Novel Gabapentinoid Mirogabalin Prevents Upregulation of α2δ-1 Subunit of Voltage-Gated Calcium Channels in Spinal Dorsal Horn in a Rat Model of Spinal Nerve Ligation

Gabapentinoids are specific ligands for the α₂δ-1 subunit of voltage-gated calcium channels. This class of drugs, including gabapentin and pregabalin, exert various pharmacological effects and are widely used for the treatment of epilepsy, anxiety, and chronic pain. The mechanism of action of gabapentinoids involves both direct modulation of calcium channel kinetics and inhibition of channel trafficking and expression, which contribute to the above pharmacological effects. In the present study, we investigated the effects of mirogabalin, a novel potent gabapentinoid, on expression levels of the α₂δ-1 subunit in the spinal dorsal horn in a rat model of spinal nerve ligation (SNL) as an experimental animal model for peripheral neuropathic pain. The neuropathic pain state was induced by SNL in male Sprague - Dawley rats. After the development of mechanical hypersensitivity, the animals received 10 mg/kg mirogabalin or vehicle orally for 5 consecutive days and were subjected to immunohistochemical analysis of α₂δ-1 subunit expression in the spinal cord. In the SNL model rats, expression of the α₂δ-1 subunit significantly increased in the spinal dorsal horn at the ipsilateral side of nerve injury, while mirogabalin inhibited this increase. In conclusion, the α₂δ-1 subunit was upregulated in the spinal dorsal horn of SNL model rats, and repeated administration of mirogabalin inhibited this upregulation. The inhibitory effect of mirogabalin on upregulation of the α₂δ-1 subunit after nerve injury is considered to contribute to its analgesic effects in peripheral neuropathic pain.

Gabapentin-Friend or foe?

BACKGROUND

Gabapentin is a recommended first-line agent for treating neuropathic pain; however, its efficacy rate is reportedly low, and the risk of adverse events is high. A plausible explanation for this lies with its wide range of actions, the entirety of which have yet to be fully elucidated.

METHODS

A review of the literature was conducted on gabapentin's known and proposed analgesic mechanisms of action, as well as potentially opposing or detrimental actions.

RESULTS

Gabapentin's classical analgesic mechanisms involve direct attenuation of excitatory neurotransmission in the spinal cord via inhibition of neuronal ion channels, while indirect mechanisms include descending inhibition and block of injury-evoked synaptogenesis. Glial effects have also been reported; however, whether they are neuroprotective or detrimental is unknown. Furthermore, data from animal models do not reflect clinical outcomes.

CONCLUSIONS

Gabapentin's clinical use should be reconsidered according to the net effects of its numerous assumed actions, including the tripartite synapse and oligodendrocyte effects. Whether it is doing more harm than good, especially in the scenarios of incomplete or loss of response, warrants consideration when prescribing gabapentin.

The Clinical Application and Progress of Mirogabalin on Neuropathic Pain as a Novel Selective Gabapentinoids

Background

Neuropathic pain is a complex sort of pain that is detrimental to individuals' health, both physically and mentally, but merely a small portion of them could witness pain alleviation. Mirogabalin, by distinctive binding characteristics of voltage-gated calcium channels, has won approval from the Japanese authority as a third member of gabapentinoids in Japan. Our review was aimed at encompassing the bulk of clinical research on mirogabalin, which included clinical trials, special considerations, coadministration studies, case reports, and cost-effectiveness studies.

Methods

A review was carried out on a series of platforms, such as PubMed, MEDLINE, and Scopus, up to December 2021 using the keywords as follows: "mirogabalin OR mirogabalin besylate OR Tarlige OR DS-5565" AND "neuropathic pain OR Neuropathy."

Results

Mirogabalin demonstrated analgesic activity and manageable adverse reactions and provides a new alternative for individuals with PHN or DPNP in 3 phase II and 4 III trials. Mirogabalin alleviated pain markedly in comparison with placebo. Administration of mirogabalin on a long-term basis is a flexible dosage regimen for patients with PHN. It is noteworthy that mirogabalin should be administrated cautiously when combined with probenecid and cimetidine on account of a slight increase in pharmacodynamics effects of mirogabalin.

Conclusion

The development of mirogabalin allows further optimization of individual treatment strategies so as to provide more therapeutic choices in this medical domain.

Persistent sensory changes and sex differences in transgenic mice conditionally expressing HIV-1 Tat regulatory protein

HIV-associated sensory neuropathies (HIV-SN) are prevalent in >50% of patients aged over 45 years many of which report moderate to severe chronic pain. Previous preclinical studies have investigated the mechanisms by which HIV-1 causes sensory neuropathies and pain-like behaviors. The aim of the present study is to delineate the role of chronic HIV-1 trans-activator of transcription protein (Tat) exposure in the development of neuropathy in mice. The temporal effects of conditional Tat expression on the development of hypersensitivity to mechanical (von Frey filaments) and thermal (heat or cold) stimuli were tested in male and female mice that transgenically expressed HIV-1 Tat in a doxycycline-inducible manner. Inducing Tat expression produced an allodynic response to mechanical or cold (but not heat) stimuli that respectively persisted for at least 23-weeks (mechanical hypersensitivity) or at least 8-weeks (cold hypersensitivity). Both allodynic states were greater in magnitude among females, compared to males, and mechanical increased hypersensitivity progressively in females over time. Acute morphine or gabapentin treatment partly attenuated allodynia in males, but not females. Irrespective of sex, Tat reduced intraepidermal nerve fiber density, the mean amplitude of sensory nerve action potentials (but not conductance), engagement in some pain-related ethological behaviors (cage-hanging and rearing), and down-regulated PPAR-α gene expression in lumbar spinal cord while upregulating TNF-α expression in dorsal root ganglion. Taken together, these data reveal fundamental sex differences in mechanical and cold hypersensitivity in response to Tat and demonstrate the intractable nature in female mice to current therapeutics. Understanding the role of Tat in these pathologies may aid the design of future therapies aimed at mitigating the peripheral sensory neuropathies that accompany neuroHIV.

Antinociceptive efficacy of Clerodendrum petasites S. Moore, a Thai medicinal plant, and its CNS safety profiles

Background

Clerodendrum petasites, an herbal plant in Thailand, has been used for many years in folk medicine. However, scientific evidence regarding CNS safety pharmacology and antinociceptive activity of C. petasites (CP) has not yet been well characterized.

Purpose

The present study aimed to assess the CNS safety pharmacology and antinociceptive and antiinflammatory effects of CP extract.

Methods

The effect of CP extract on CNS safety pharmacology was assessed using LABORAS automated home cage monitoring and rotarod test. Its pharmacological activity was evaluated both in-vitro, and in-vivo using hot-plate, acetic acid-induced writhing, formalin, and carrageenan-induced paw edema models.

Results and conclusion

CP extract significantly improved thermal and chemical nociceptive behaviors and acute inflammatory pain at all doses: 300, 600, and 1200 mg/kg, p.o. The antiinflammatory effect of CP extract in inflammatory pain models was comparable to the effect of positive control: indomethacin 10 mg/kg at all dose levels tested. Further, the CP extract at 600 mg/kg dose significantly inhibited 82.3% of carrageenan-induced total edema. In-vitro, CP extract at 12.5, 25, and 50 μg/mL concentrations significantly reduced the expression of LPS-induced nitric oxide, IL-6, and TNF-α expression in both RAW 264.7 macrophage and BV-2 microglial cell lines. In addition, CP extract did not show any potential effects on the CNS, indicated by no significant effects on motor coordination, spontaneous locomotor activity, general behaviors, and well-being compared to vehicle-treated mice (p > 0.05). Overall, the present study evidences the potential antinociceptive, antiinflammatory efficacies of CP extract with a favorable CNS safety profile.

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.

Pain Management in Older Adults with Chronic Wounds

Older people often suffer from different types of ulcers, with the most prevalent being chronic leg ulcers (CLUs) and diabetic foot ulcers. There are major issues in the current medical approach because these ulcers are hard to heal, and, in the case of CLUs, very painful and with a high frequency of relapse. Older people complain of pain more frequently than young people, frequently due to a combination of painful chronic wounds with other comorbidities (e.g. arthritis, peripheral arterial disease, vertebrogenic pain syndrome). However, chronic pain appears to be managed better by older people because the pain sensitivity is downregulated and the pain threshold is higher in older people. Pain management of chronic wounds is often insufficient, especially in older individuals. It is highly important to use non-traumatic wound dressings and pay attention to patients' feelings and fears because pain in chronic ulcers can impair wound healing. Key factors include good preparation for dressing change and adequate analgesia, ideally a combination of topical and oral agents.

Gabapentin Alleviates Brain Injury in Intracerebral Hemorrhage Through Suppressing Neuroinflammation and Apoptosis

Neuroinflammation plays an important role in brain tissue injury during intracerebral hemorrhage. Gabapentin can reduce inflammation and oxidative stress through inhibiting nuclear factor κB (NFκB) signals. Here, we showed that gabapentin reduced brain tissue injury in ICH through suppressing NFκB-mediated neuroinflammation. ICH was induced by injecting collagenase IV into the right striatum of Sprague-Dawley rats. PC12 and BV2 cells injury induced by Hemin were used to simulate ICH in vitro. Inflammation and apoptosis were assessed in rat brain tissue and in vitro cells. The neurobehavioral scores were significantly decreased in ICH rats compared with sham rats. Phosphorylated IκB-α and cleaved caspase3, and apoptosis rate were significantly higher in tissue surrounding the hematoma than in brain tissues from rats subjected to sham surgery. Furthermore, serum IL-6 levels in ICH rats were higher than in sham rats. Gabapentin treatment significantly improved the behavioral scores, decreased levels of phosphorylated IκB-α and cleaved caspase3, apoptosis rate, and serum IL-6 level in ICH rats. Hemin-treated BV2 cells displayed higher levels of phosphorylated IκB-α, cleaved caspase3, and IL-6 in the supernatant compared with vehicle-treated cells. Hemin treatment induced a significantly lower level of peroxisome proliferator-activated receptor γ (PPARγ) in BV2 cells. BV2-PC12 co-culture cells treated by hemin displayed higher levels of cleaved caspase3 in PC12 cells. Furthermore, gabapentin treatment could reduce these effects induced by hemin and the protective effects of gabapentin were significantly attenuated by PPARγ inhibitor. Therefore, gabapentin may reduce inflammation and apoptosis induced by the ICH through PPARγ-NFκB pathway.

Pharmacotherapeutic management of trigeminal neuropathic pain: an update

INTRODUCTION

Guidelines recommend a number of pharmacotherapeutic options used as monotherapy or in combination with others for treating the pain of trigeminal neuropathy.

AREAS COVERED

The authors examine the pharmacotherapeutic options for treating trigeminal neuralgia and supporting evidence in the literature. Guidelines reported the most effective treatment for trigeminal neuropathy, in particular trigeminal neuralgia, appears to be carbamazepine or oxcabazepine, but side effects can be treatment limiting. Lamotrigine and gabapentin are also recommended in guidance. In real-world clinical practice, baclofen, cannabinoids, eslicarbazepine, levetiracetam, brivaracetam, lidocaine, misoprostol, opioids, phenytoin, fosphenytoin, pimozide, sodium valproate, sumatriptan, tizanidine, tocainide, tricyclic antidepressants, and vixotrigine are sometimes used, either as monotherapy or in combination. The relatively small patient population has limited the number of large-scale studies and there is limited evidence on which to base prescribing choices.

EXPERT OPINION

While there is no optimal pharmacotherapy for treating trigeminal neuropathy, advancements in our understanding of the underlying mechanisms of this condition and drug development indicate promise for NaV inhibitors, despite the fact that not all patients respond to them and they may have potentially treatment-limiting side effects. Nevertheless, better understanding of NaV channels may be important avenues for future drug development for trigeminal neuropathy.

Regional anesthesia and acute perioperative pain management in thoracic surgery: a narrative review

Background and Objective

Thoracic surgery causes significant pain which can negatively affect pulmonary function and increase risk of postoperative complications. Effective analgesia is important to reduce splinting and atelectasis. Systemic opioids and thoracic epidural analgesia (TEA) have been used for decades and are effective at treating acute post-thoracotomy pain, although both have risks and adverse effects. The advancement of thoracoscopic surgery, a focus on multimodal and opioid-sparing analgesics, and the development of ultrasound-guided regional anesthesia techniques have greatly expanded the options for acute pain management after thoracic surgery. Despite the expansion of surgical techniques and analgesic approaches, there is no clear optimal approach to pain management. This review aims to summarize the body of literature regarding systemic and regional anesthetic techniques for thoracic surgery in both thoracotomy and minimally invasive approaches, with a goal of providing a foundation for providers to make individualized decisions for patients depending on surgical approach and patient factors, and to discuss avenues for future research.

Methods

We searched PubMed and Google Scholar databases from inception to May 2021 using the terms “thoracic surgery”, “thoracic surgery AND pain management”, “thoracic surgery AND analgesia”, “thoracic surgery AND regional anesthesia”, “thoracic surgery AND epidural”. We considered articles written in English and available to the reader.

Key Content and Findings

There is a wide variety of strategies for treating acute pain after thoracic surgery, including multimodal opioid and non-opioid systemic analgesics, regional anesthesia including TEA and paravertebral blocks (PVB), and a recent expansion in the use of novel fascial plane blocks especially for thoracoscopy. The body of literature on the effectiveness of different approaches for thoracotomy and thoracoscopy is a rapidly expanding field and area of active debate.

Conclusions

The optimal analgesic approach for thoracic surgery may depend on patient factors, surgical factors, and institutional factors. Although TEA may provide optimal analgesia after thoracotomy, PVB and emerging fascial plane blocks may offer effective alternatives. A tailored approach using multimodal systemic therapies and regional anesthesia is important, and future studies comparing techniques are necessary to further investigate the optimal approach to improve patient outcomes.

Opioid Use Consequences, Governmental Strategies, and Alternative Pain Control Techniques Following Total Hip Arthroplasties

Over the last several decades, rates of opioid use and associated problems have dramatically increased in the United States leading to laws limiting prescription duration for acute pain management. As a result, orthopedic surgeons who perform total hip arthroplasty (THA), a procedure that often leads to significant postoperative pain, have been faced with substantial challenges to adequately mitigate patient pain while also reducing opioid intake. Current strategies include identifying and correcting modifiable risk factors associated with postoperative opioid use such as preoperative opioid use, alcohol and tobacco abuse, and untreated psychiatric illness. Additionally, recent evidence has emerged in the form of Enhanced Recovery After Surgery (ERAS) protocols suggesting that a multidisciplinary focus on patient factors perioperatively can lead to reduced postoperative opioid administration and decreased hospital stays. A cornerstone of ERAS protocols includes multimodal pain regimens with opioid rescue only as needed, which often includes multiple systemic pain therapies such as acetaminophen, gabapentin, non-steroidal anti-inflammatory drugs, as well as targeted pain therapies that include epidural catheters and ultrasound-guided nerve blocks. Many hospital systems and states have also implemented opioid prescribing limitations with mixed success. As the opioid epidemic continues in the United States, while contributing to poor outcomes following elective surgeries, further research is warranted to identify multidisciplinary strategies that mitigate opioid use while also allowing for adequate pain control and rehabilitation.

The Effect of Pregabalin on the Minimum Alveolar Concentration of Sevoflurane: A Randomized, Placebo-Controlled, Double-Blind Clinical Trial

Background

Pregabalin is commonly used perioperatively to reduce post-operative pain and opioid consumption and to prevent the development of chronic pain. It has been shown to reduce anesthetic consumption in balanced anesthesia, but studies investigating its effect on the minimum alveolar concentration (MAC) of volatile anesthetics are lacking. The aim of this study was to investigate the effect of two different doses of pregabalin on the MAC of sevoflurane.

Methods

In a randomized, double-blinded, placebo controlled clinical study, 75 patients were assigned to receive placebo, 300 mg pregabalin, or 150 mg pregabalin, as a capsule 1 h before anesthesia induction with sevoflurane only. After equilibration, the response to skin incision (movement vs. non-movement) was monitored. The MAC was assessed using an up- and down-titration method.

Results

The MAC of sevoflurane was estimated as 2.16% (95% CI, 2.07–2.32%) in the placebo group, 1.44% (95% CI, 1.26–1.70%) in the 300 mg pregabalin group, and 1.81% (95% CI, 1.49–2.13%) in the 150 mg pregabalin group. We therefore report a 33% reduction in the MAC of sevoflurane in the 300 mg pregabalin group as compared to placebo. The MAC of the 150 mg pregabalin group was reduced by 16% as compared to placebo but was not statistically significant.

Conclusions

The administration of 300 mg pregabalin reduced the MAC of sevoflurane by 33%, while the administration of 150 mg pregabalin did not significantly reduce the MAC of sevoflurane. Pregabalin use led to a small reduction in post-operative pain levels but increased side effects in a dose-dependent manner.

Systematic Review of Voltage-Gated Calcium Channel α2δ Subunit Ligands for the Treatment of Chronic Neuropathic Pain and Insight into Structure-Activity Relationship (SAR) by Pharmacophore Modeling

BACKGROUND

Neuropathic pain (NP) is a complex symptom related to the nerve damage. The discovery of new drugs for treating chronic NP has been continuing for several decades, while more progress is still needed to be made because of the unsatisfactory efficacy and the side effects of the currently available drugs. Among all the approved drugs for chronic NP, voltage-gated calcium channel (VGCC) α2δ subunit ligands, also known as gabapentinoids, are among the first-line treatment and represent a class of efficacious and relatively safe therapeutic agents. However, new strategies are still needed to be explored due to the unsatisfied response rate.

OBJECTIVES

To review the latest status of the discovery and development of gabapentinoids for the treatment of chronic NP by covering both the marketed and the preclinical/clinical ones. To analyze the structure-activity relationship (SAR) of gabapentinoids to facilitate the future design of structurally novel therapeutic agents targeting VGCC α2δ subunit.

METHODS

We searched PubMed Central, Embase, Cochrane Library, Web of Science, Scopus and Espacenet for the literature and patents of diabetic peripheral neuropathic pain, postherpetic neuralgia, fibromyalgia, voltage-gated calcium channel α2δ subunit and related therapeutic agents from incipient to June 10, 2021. The SAR of gabapentinoids were analyzed by pharmacophore modeling using Phase module in Schrödinger suite.

RESULTS

A variety of gabapentinoids were identified as VGCC α2δ ligands that have ever been under development for the treatment of chronic NP. Among them, four gabapentinoids are marketed, one is at the active late clinical trials, and eight have been discontinued. Pharmacophore models were generated by using Phase module in Schrödinger suite, and common pharmacophores were predicted based on pharmacophoric features and analyzed.

CONCLUSION

The latest progress of the discovery and development of gabapentinoids for the treatment of chronic NP was reviewed. Moreover, the structure-activity relationship (SAR) of gabapentinoids is analyzed by pharmacophore modeling, which will be valuable for the future design of structurally novel therapeutic agents targeting VGCC α2δ subunit.

Effects of Gabapentin Enacarbil on Postoperative Pain After Hip and Knee Arthroplasty: A Placebo-controlled Randomized Trial

OBJECTIVES

Total joint arthroplasties are among the most common elective procedures performed in the United States, and they are associated with postoperative pain. Gabapentin enacarbil is a prodrug with an extended-release formulation that has been proposed for multimodal postoperative analgesia, but the drug's efficacy for major arthroplasties remains unclear.

MATERIALS AND METHODS

We enrolled 60 adult patients scheduled for primary knee or hip arthroplasty expected to remain hospitalized for at least 3 days. Eligible patients were randomly assigned to placebo or gabapentin enacarbil 600 mg twice daily starting the day before surgery continuing for 3 days thereafter.The primary outcome was analyzed using a joint hypothesis framework of pain (0 to 10 verbal response scores) and cumulative opioid consumption (mg of morphine equivalent) within the first 72 hours. Secondary outcomes were nausea and vomiting, pain persisting 90 days after surgery, duration of hospitalization, and early postoperative health status using quality of recovery score (QoR-15).

RESULTS

Twenty-eight patient in gabapentin enacarbil group and 32 in placebo group were analyzed. Since pain scores did not differ significantly (difference of means: -0.2 in pain scores; 95% confidence interval: -1.1, 0.7), nor did opioid consumption, conditions for joint hypothesis testing were not met. Moreover, there were no significant differences between groups for secondary outcomes.

DISCUSSION

We did not identify statistically significant or clinically meaningful differences in our primary and secondary outcomes related to perioperative use of gabapentin enacarbil in patients having primary hip or knee arthroplasties.

The Routes of Administration for Acute Postoperative Pain Medication

Effective treatment of postoperative acute pain, together with early mobilization and nutrition, is one of the perioperative strategies advocated to improve surgical outcome and reduce the costs of hospitalization. Moreover, adequate pain control reduces perioperative morbidity related to surgical stress and can also prevent the incidence of chronic postoperative pain syndromes, whose treatment is still a challenge. The choice of the most appropriate analgesics depends not only on the drug class, but also on the most suitable route of administration, the best dosage for that route, and unique limitations and contraindications for every patient. In the present review, a comprehensive analysis was performed on the different routes of administration of acute postoperative pain medications and their indications and limitations, focusing on recent evidence and international recommendations.