Antiepileptic drugs for the treatment of neuropathic pain: a systematic review

Systematic review of pharmacotherapy for atypical facial pain: evaluation of pain reduction, depression, anxiety and quality of life

BACKGROUND/PURPOSE

Atypical facial pain (AFP) is a chronic condition characterized by persistent facial pain without clear clinical signs, making diagnosis and treatment difficult. Common pharmacological treatments include antidepressants, anticonvulsants and neuromodulators, but their effectiveness remains uncertain, necessitating a systematic review to guide clinical practice.

MATERIALS AND METHODS

Following PRISMA 2020 guidelines, randomized controlled trials (RCTs) evaluating pharmacological treatments for AFP in adults were included. A comprehensive search of five databases without date restrictions was performed. Data on pain reduction, quality of life, and adverse events were extracted. The Cochrane Risk of Bias (RoB 2.0) tool assessed bias, and evidence quality was evaluated using the Critical Appraisal Skills Programme tool.

RESULTS

Out of 196 studies identified, 10 RCTs met the inclusion criteria. Pharmacological responses varied significantly across studies. Antidepressants such as dothiepin and clomipramine demonstrated significant pain reduction, whereas venlafaxine showed limited efficacy. However, onabotulinum toxin A and sumatriptan exhibited inconsistent or minimal effects on AFP pain intensity. Adverse events were reported across multiple treatments, ranging from mild side effects such as dry mouth and nausea to severe reactions like diplopia and facial asymmetry, which impacted adherence. Despite some positive outcomes, the heterogeneity in study methodologies, outcome measures, and follow-up durations limited direct comparisons between interventions.

CONCLUSION

This systematic review highlights the mixed efficacy of pharmacological treatments for AFP, with certain medications demonstrating superior pain relief in specific patient subgroups. Given the variability in response and adverse events, a multimodal approach combining pharmacological and non-pharmacological therapies may offer the most effective management strategy. Future research should focus on standardized treatment protocols, long-term efficacy, and personalized treatment plans to optimize patient care.

Interventions for treating pain and disability in adults with complex regional pain syndrome- an overview of systematic reviews

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually occurs in a limb following trauma or surgery. It is characterised by persisting pain that is disproportionate in magnitude or duration to the typical course of pain after similar injury. There is currently no consensus regarding the optimal management of CRPS, although a broad range of interventions have been described and are commonly used. This is the first update of the original Cochrane review published in Issue 4, 2013.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the efficacy, effectiveness, and safety of any intervention used to reduce pain, disability, or both, in adults with CRPS.

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of Ovid MEDLINE, Ovid Embase, Cochrane Database of Systematic Reviews, CINAHL, PEDro, LILACS and Epistemonikos from inception to October 2022, with no language restrictions. We included systematic reviews of randomised controlled trials that included adults (≥18 years) diagnosed with CRPS, using any diagnostic criteria.  Two overview authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools respectively. We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes quality of life, emotional well-being, and participants' ratings of satisfaction or improvement with treatment.  MAIN RESULTS: We included six Cochrane and 13 non-Cochrane systematic reviews in the previous version of this overview and five Cochrane and 12 non-Cochrane reviews in the current version. Using the AMSTAR 2 tool, we judged Cochrane reviews to have higher methodological quality than non-Cochrane reviews. The studies in the included reviews were typically small and mostly at high risk of bias or of low methodological quality. We found no high-certainty evidence for any comparison.  There was low-certainty evidence that bisphosphonates may reduce pain intensity post-intervention (standardised mean difference (SMD) -2.6, 95% confidence interval (CI) -1.8 to -3.4, P = 0.001; I2 = 81%; 4 trials, n = 181) and moderate-certainty evidence that they are probably associated with increased adverse events of any nature (risk ratio (RR) 2.10, 95% CI 1.27 to 3.47; number needed to treat for an additional harmful outcome (NNTH) 4.6, 95% CI 2.4 to 168.0; 4 trials, n = 181).  There was moderate-certainty evidence that lidocaine local anaesthetic sympathetic blockade probably does not reduce pain intensity compared with placebo, and low-certainty evidence that it may not reduce pain intensity compared with ultrasound of the stellate ganglion. No effect size was reported for either comparison. There was low-certainty evidence that topical dimethyl sulfoxide may not reduce pain intensity compared with oral N-acetylcysteine, but no effect size was reported. There was low-certainty evidence that continuous bupivacaine brachial plexus block may reduce pain intensity compared with continuous bupivacaine stellate ganglion block, but no effect size was reported. For a wide range of other commonly used interventions, the certainty in the evidence was very low and provides insufficient evidence to either support or refute their use. Comparisons with low- and very low-certainty evidence should be treated with substantial caution. We did not identify any RCT evidence for routinely used pharmacological interventions for CRPS such as tricyclic antidepressants or opioids.

AUTHORS' CONCLUSIONS

Despite a considerable increase in included evidence compared with the previous version of this overview, we identified no high-certainty evidence for the effectiveness of any therapy for CRPS. Until larger, high-quality trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult. Current non-Cochrane systematic reviews of interventions for CRPS are of low methodological quality and should not be relied upon to provide an accurate and comprehensive summary of the evidence.

Inhibition of Fast Nerve Conduction Produced by Analgesics and Analgesic Adjuvants-Possible Involvement in Pain Alleviation

Nociceptive information is transmitted from the periphery to the cerebral cortex mainly by action potential (AP) conduction in nerve fibers and chemical transmission at synapses. Although this nociceptive transmission is largely inhibited at synapses by analgesics and their adjuvants, it is possible that the antinociceptive drugs inhibit nerve AP conduction, contributing to their antinociceptive effects. Many of the drugs are reported to inhibit the nerve conduction of AP and voltage-gated Na⁺ and K⁺ channels involved in its production. Compound action potential (CAP) is a useful measure to know whether drugs act on nerve AP conduction. Clinically-used analgesics and analgesic adjuvants (opioids, non-steroidal anti-inflammatory drugs, ₂-adrenoceptor agonists, antiepileptics, antidepressants and local anesthetics) were found to inhibit fast-conducting CAPs recorded from the frog sciatic nerve by using the air-gap method. Similar actions were produced by antinociceptive plant-derived chemicals. Their inhibitory actions depended on the concentrations and chemical structures of the drugs. This review article will mention the inhibitory actions of the antinociceptive compounds on CAPs in frog and mammalian peripheral (particularly, sciatic) nerves and on voltage-gated Na⁺ and K⁺ channels involved in AP production. Nerve AP conduction inhibition produced by analgesics and analgesic adjuvants is suggested to contribute to at least a part of their antinociceptive effects.

Pressure pain assessment may predict the outcome of spinal cord stimulation for refractory epilepsy

It was well-documented that epilepsy and pain arise from an excitation-inhibition imbalance within neuronal networks. A previous meta-analysis of data from clinical trials showed an association between anticonvulsants and specific pain types, e.g. multiple sclerosis pain. Multiple multicentre randomized controlled trials have shown that antiepileptic drugs have a prominent role in the treatment of several types of pain, e.g. neuropathic pain. Many anticonvulsants have been introduced to better manage acute postoperative pain, with improvements in analgesic efficacy and safety. These data suggested that there existed the similar mechanisms of certain forms of epilepsy and pain, and the therapeutic mechanism of spinal cord stimulation for certain forms of epilepsy and pain may be involved in the melanocortinergic signaling, and the change in cerebral glucose metabolism. We hypothesized that pressure pain assessment may predict the outcome of spinal cord stimulation in refractory epilepsy.

Injury-induced maladaptation and dysregulation of calcium channel α2 δ subunit proteins and its contribution to neuropathic pain development

Voltage-gated calcium channels (VGCCs) play important roles in physiological functions including the modulation of neurotransmitter release, neuronal network activities, intracellular signalling pathways and gene expression. Some pathological conditions, including nerve injuries, can cause the dysregulation of VGCCs and their subunits. This in turn can lead to a functional maladaptation of VGCCs and their subunits, which can contribute to the development of disorders such as pain sensations. This review has summarized recent findings related to maladaptive changes in the dysregulated VGCC α2 δ1 subunit (Cav α2 δ1 ) with a focus on exploring the mechanisms underlying the contribution of Cav α2 δ1 to pain signal transduction. At least under neuropathic pain conditions, the dysregulated Cav α2 δ1 can modulate VGCC functions as well as other plasticity changes. The latter includes abnormal excitatory synaptogenesis resulting from its interactions with injury-induced extracellular matrix glycoprotein molecule thrombospondins, which is independent of the VGCC functions. Blocking Cav α2 δ1 with gabapentinoids can reverse neuropathic pain significantly with relatively mild side effects, but only in a small population of neuropathic pain patients due to reasons yet to be explored. There are emerging data suggesting that early preventive treatment with gabapentinoids can prevent aberrant excitatory synapse formation and the development of chronic pain. If these findings are confirmed clinically, this could be an attractive approach for neuropathic pain management.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

Management of chronic neuropathic pain: a protocol for a multiple treatment comparison meta-analysis of randomised controlled trials

INTRODUCTION

Chronic neuropathic pain is associated with reduced health-related quality of life and substantial socioeconomic costs. Current research addressing management of chronic neuropathic pain is limited. No review has evaluated all interventional studies for chronic neuropathic pain, which limits attempts to make inferences regarding the relative effectiveness of treatments.

METHODS AND ANALYSIS

We will conduct a systematic review of all randomised controlled trials evaluating therapies for chronic neuropathic pain. We will identify eligible trials, in any language, by a systematic search of CINAHL, EMBASE, MEDLINE, AMED, HealthSTAR, DARE, PsychINFO and the Cochrane Central Registry of Controlled Trials. Eligible trials will be: (1) enrol patients presenting with chronic neuropathic pain, and (2) randomise patients to alternative interventions (pharmacological or non-pharmacological) or an intervention and a control arm. Pairs of reviewers will, independently and in duplicate, screen titles and abstracts of identified citations, review the full texts of potentially eligible trials and extract information from eligible trials. We will use a modified Cochrane instrument to evaluate risk of bias of eligible studies, recommendations from the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) to inform the outcomes we will collect, and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system to evaluate our confidence in treatment effects. When possible, we will conduct: (1) in direct comparisons, a random-effects meta-analysis to establish the effect of reported therapies on patient-important outcomes; and (2) a multiple treatment comparison meta-analysis within a Bayesian framework to assess the relative effects of treatments. We will define a priori hypotheses to explain heterogeneity between studies, and conduct meta-regression and subgroup analyses consistent with the current best practices.

ETHICS AND DISSEMINATION

We do not require ethics approval for our proposed review. We will disseminate our findings through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

PROSPERO (CRD42014009212).

Systematic review and meta-analysis of pharmacological therapies for pain associated with postherpetic neuralgia and less common neuropathic conditions

OBJECTIVE

To estimate the relative efficacy of pharmacological therapies for the treatment of postherpetic neuralgia (PHN), multiple sclerosis (MS)-related pain, posttraumatic pain, central poststroke pain (CPSP) and human immunodeficiency virus (HIV)-related neuropathic pain (NeP).

METHODS

This systematic review (through June 2011) identified randomised, controlled trials of treatments for these conditions. Bayesian mixed treatment comparison (MTC) methods were used to determine the relative efficacy and safety among the treatments within each pain condition.

RESULTS

Fifty studies were identified: 33 PHN, 2 MS-related pain, 3 CPSP, 3 posttraumatic pain and 9 HIV-related NeP. Data from 28 PHN studies including 21 interventions and 4317 patients were included into the PHN MTC. Of treatments studied in ≥ 50 patients, opioids had the greatest mean pain reduction of -1.70 vs. placebo on an 11-point numeric rating scale. Pregabalin ≥ 300 mg/day was most effective for ≥ 30% and ≥ 50% pain reduction [relative risk (RR) vs. placebo = 2.44 and 2.13, respectively]. Data identified for MS-related pain, CPSP, posttraumatic pain and HIV-related NeP were sparse; only 7 of 17 studies had ≥ 50 patients. Adverse events (AEs) and discontinuations for most treatments were not significantly greater than placebo except in PHN, where 8 of 12 treatments had higher risks of AEs compared with placebo and tricyclic antidepressants and opioids had higher risk of discontinuation compared with placebo.

CONCLUSIONS

Guideline-recommended treatments for PHN were more effective than placebo on the pain NRS and for ≥ 30% and ≥ 50% pain reduction. Although guidelines exist for the management of less common NeP conditions, little published evidence supports them. These results highlight the need for additional evaluations and more complete reporting of outcomes to help guide physicians' treatment selections.

Effects of various antiepileptics used to alleviate neuropathic pain on compound action potential in frog sciatic nerves: comparison with those of local anesthetics

Antiepileptics used for treating neuropathic pain have various actions including voltage-gated Na(+) and Ca(2+) channels, glutamate-receptor inhibition, and GABA(A)-receptor activation, while local anesthetics are also used to alleviate the pain. It has not been fully examined yet how nerve conduction inhibitions by local anesthetics differ in extent from those by antiepileptics. Fast-conducting compound action potentials (CAPs) were recorded from frog sciatic nerve fibers by using the air-gap method. Antiepileptics (lamotrigine and carbamazepine) concentration dependently reduced the peak amplitude of the CAP (IC50 = 0.44 and 0.50 mM, resp.). Carbamazepine analog oxcarbazepine exhibited an inhibition smaller than that of carbamazepine. Antiepileptic phenytoin (0.1 mM) reduced CAP amplitude by 15%. On the other hand, other antiepileptics (gabapentin, sodium valproate, and topiramate) at 10 mM had no effect on CAPs. The CAPs were inhibited by local anesthetic levobupivacaine (IC50 = 0.23 mM). These results indicate that there is a difference in the extent of nerve conduction inhibition among antiepileptics and that some antiepileptics inhibit nerve conduction with an efficacy similar to that of levobupivacaine or to those of other local anesthetics (lidocaine, ropivacaine, and cocaine) as reported previously. This may serve to know a contribution of nerve conduction inhibition in the antinociception by antiepileptics.

Chloride extrusion enhancers as novel therapeutics for neurological diseases

The K(+)-Cl(-) cotransporter KCC2 is responsible for maintaining low Cl(-) concentration in neurons of the central nervous system (CNS), which is essential for postsynaptic inhibition through GABA(A) and glycine receptors. Although no CNS disorders have been associated with KCC2 mutations, loss of activity of this transporter has emerged as a key mechanism underlying several neurological and psychiatric disorders, including epilepsy, motor spasticity, stress, anxiety, schizophrenia, morphine-induced hyperalgesia and chronic pain. Recent reports indicate that enhancing KCC2 activity may be the favored therapeutic strategy to restore inhibition and normal function in pathological conditions involving impaired Cl(-) transport. We designed an assay for high-throughput screening that led to the identification of KCC2 activators that reduce intracellular chloride concentration ([Cl(-)]i). Optimization of a first-in-class arylmethylidine family of compounds resulted in a KCC2-selective analog (CLP257) that lowers [Cl(-)]i. CLP257 restored impaired Cl(-) transport in neurons with diminished KCC2 activity. The compound rescued KCC2 plasma membrane expression, renormalized stimulus-evoked responses in spinal nociceptive pathways sensitized after nerve injury and alleviated hypersensitivity in a rat model of neuropathic pain. Oral efficacy for analgesia equivalent to that of pregabalin but without motor impairment was achievable with a CLP257 prodrug. These results validate KCC2 as a druggable target for CNS diseases.

Systematic review and comparison of pharmacologic therapies for neuropathic pain associated with spinal cord injury

BACKGROUND

Management of neuropathic pain (NeP) associated with spinal cord injury (SCI) is difficult. This report presents a systematic literature review and comparison of the efficacy and safety of pharmacologic therapies for treating SCI-associated NeP.

METHODS

Medline, Embase, Cochrane, and Database of Abstracts of Reviews of Effects were searched through December 2011 for randomized, blinded, and controlled clinical trials of SCI-associated NeP meeting predefined inclusion criteria. Efficacy outcomes of interest were pain reduction on the 11-point numeric rating scale (NRS) or 100 mm visual analog scale and proportion of patients achieving ≥30% or ≥50% pain reduction. Discontinuations and adverse events (AEs) were also assessed, for which Bayesian meta-analytic indirect comparisons were performed.

RESULTS

Of the nine studies included in the analysis, samples were <100 patients, except for one pregabalin study (n = 136). Standard errors for the NRS outcome were often not reported, precluding quantitative comparisons across treatments. Estimated 11-point NRS pain reduction relative to placebo was -1.72 for pregabalin, -1.65 for amitriptyline, -1.0 for duloxetine, -1 (median) for levetiracetam, -0.27 for gabapentin, 1 (median) for lamotrigine, and 2 for dronabinol. Risk ratios relative to placebo for 30% improvement were 0.71 for levetiracetam and 2.56 for pregabalin, and 0.94 and 2.91, respectively, for 50% improvement. Meta-analytic comparisons showed significantly more AEs with pregabalin and tramadol compared with placebo, and no differences between placebo and any treatment for discontinuations.

CONCLUSIONS

Studies of SCI-associated NeP were few, small, and reported insufficient data for quantitative comparisons of efficacy. However, available data suggested pregabalin was associated with more favorable efficacy for all outcome measures examined, and that the risks of AEs and discontinuations were found to be similar among the therapies.

Systematic review and meta-analysis of pharmacological therapies for painful diabetic peripheral neuropathy

BACKGROUND

Painful diabetic peripheral neuropathy (pDPN) is prevalent among persons with diabetes and increases over time. Published guidelines recommend a number of medications to treat this condition providing clinicians with a variety of treatment options. This study provides a comprehensive systematic review and meta-analysis of published pharmacologic therapies for pDPN.

METHODS

The published literature was systematically searched to identify randomized, controlled trials of all available pharmacologic treatments for pDPN (recommended or nonrecommended) reporting predefined efficacy and safety outcomes. Bayesian fixed-effect mixed treatment comparison methods were used to assess relative therapeutic efficacy and harms.

RESULTS

Data from 58 studies including 29 interventions and 11,883 patients were analyzed. Pain reduction over that of placebo on the 11-point numeric rating scale ranged from -3.29 for sodium valproate (95% credible interval [CrI] = [-4.21, -2.36]) to 1.67 for Sativex (-0.47, 0.60). Estimates for most treatments were clustered between 0 and -1.5 and were associated with more study data and smaller CrIs. Pregabalin (≥ 300 mg/day) was the most effective on the 100-point visual analog scale (-21.88; [-27.06, -16.68]); topiramate was the least (-3.09; [-3.99, -2.18]). Relative risks (RRs) of 30% pain reduction ranged from 0.78 (Sativex) to 1.84 (lidocaine 5% plaster). Analysis of the RR ratio of these 2 treatments reveals marginal significance for Sativex (3.27; [1.07, 9.81]), indicating the best treatment is only slightly better than the worst. Relative risks of 50% pain reduction ranged from 0.98 (0.56, 1.52) (amitriptyline) to 2.25 (1.51, 3.00) (alpha-lipoic acid). RR ratio for these treatments was not statistically different (3.39; [0.88, 3.34]). Fluoxetine had the lowest risk of adverse events (0.94; [0.62, 1.23]); oxycodone had the highest (1.55; [1.45, 1.64]). Discontinuation RRs were clustered around 0.8 to 1.5, with those on the extreme having greater uncertainty.

CONCLUSIONS

Selecting an appropriate pDPN therapy is key given the large number of available treatments. Comparative results revealed relative equivalence among many of the studied interventions having the largest overall sample sizes and highlight the importance of standardization of methods to effectively assess pain.