Efficacy of oral mexiletine for neuropathic pain with allodynia: a double-blind, placebo-controlled, crossover study

Clinically relevant small-molecule promotes nerve repair and visual function recovery

Adult mammalian injured axons regenerate over short-distance in the peripheral nervous system (PNS) while the axons in the central nervous system (CNS) are unable to regrow after injury. Here, we demonstrated that Lycium barbarum polysaccharides (LBP), purified from Wolfberry, accelerated long-distance axon regeneration after severe peripheral nerve injury (PNI) and optic nerve crush (ONC). LBP not only promoted intrinsic growth capacity of injured neurons and function recovery after severe PNI, but also induced robust retinal ganglion cell (RGC) survival and axon regeneration after ONC. By using LBP gene expression profile signatures to query a Connectivity map database, we identified a Food and Drug Administration (FDA)-approved small-molecule glycopyrrolate, which promoted PNS axon regeneration, RGC survival and sustained CNS axon regeneration, increased neural firing in the superior colliculus, and enhanced visual target re-innervations by regenerating RGC axons leading to a partial restoration of visual function after ONC. Our study provides insights into repurposing of FDA-approved small molecule for nerve repair and function recovery.

Systemic administration of local anesthetic agents to relieve neuropathic pain

BACKGROUND

Lidocaine, mexiletine, tocainide, and flecainide are local anesthetics which give an analgesic effect when administered orally or parenterally. Early reports described the use of intravenous lidocaine or procaine to relieve cancer and postoperative pain. Interest reappeared decades later when patient series and clinical trials reported that parenteral lidocaine and its oral analogs tocainide, mexiletine, and flecainide relieved neuropathic pain in some patients. With the recent publication of clinical trials with high quality standards, we have reviewed the use of systemic lidocaine and its oral analogs in neuropathic pain to update our knowledge, to measure their benefit and harm, and to better define their role in therapy.

OBJECTIVES

To evaluate pain relief and adverse effect rates between systemic local anesthetic-type drugs and other control interventions.

SEARCH METHODS

We searched MEDLINE (1966 through 15 May 2004), EMBASE (January 1980 to December 2002), Cancer Lit (through 15 December 2002), Cochrane Central Register of Controlled Trials (2nd Quarter, 2004), System for Information on Grey Literature in Europe (SIGLE), and LILACS, from January 1966 through March 2001. We also hand searched conference proceedings, textbooks, original articles and reviews.

SELECTION CRITERIA

We included trials with random allocation, that were double blinded, with a parallel or crossover design. The control intervention was a placebo or an analgesic drug for neuropathic pain from any cause.

DATA COLLECTION AND ANALYSIS

We collected efficacy and safety data from all published and unpublished trials. We calculated combined effect sizes using continuous and binary data for pain relief and adverse effects as primary and secondary outcome measurements, respectively.

MAIN RESULTS

Thirty-two controlled clinical trials met the selection criteria; two were duplicate articles. The treatment drugs were intravenous lidocaine (16 trials), mexiletine (12 trials), lidocaine plus mexiletine sequentially (one trial), and tocainide (one trial). Twenty-one trials were crossover studies, and nine were parallel. Lidocaine and mexiletine were superior to placebo [weighted mean difference (WMD) = -11; 95% CI: -15 to -7; P < 0.00001], and limited data showed no difference in efficacy (WMD = -0.6; 95% CI: -7 to 6), or adverse effects versus carbamazepine, amantadine, gabapentin or morphine. In these trials, systemic local anesthetics were safe, with no deaths or life-threatening toxicities. Sensitivity analysis identified data distribution in three trials as a probable source of heterogeneity. There was no publication bias.

AUTHORS' CONCLUSIONS

Lidocaine and oral analogs were safe drugs in controlled clinical trials for neuropathic pain, were better than placebo, and were as effective as other analgesics. Future trials should enroll specific diseases and test novel lidocaine analogs with better toxicity profiles. More emphasis is necessary on outcomes measuring patient satisfaction to assess if statistically significant pain relief is clinically meaningful.

The analgesic effect of intravenous methylprednisolone on acute neuropathic pain with allodynia due to central cord syndrome: a retrospective study

Background

Central cord syndrome (CCS) may be associated with severe neuropathic pain that often resists to conventional pain therapy regimens and affects the patients’ quality of life (QoL) seriously. Current treatments for CCS-associated neuropathic pain have limited evidence of efficacy. This retrospective study was performed to present the effects of early treatment with methylprednisolone (MP) on acute neuropathic pain relief and the QoL in CCS patients.

Patients and methods

Data were collected from the medical records of CCS patients who suffered from acute neuropathic pain with allodynia. All the patients received intravenous MP treatment for up to 1 week. Patients were evaluated with standard measures of efficacy: neuropathic pain intensity, the area of allodynia, and the QoL at baseline, daily treatment, and at 1 and 3 months after the end of MP treatment.

Results

Thirty-four eligible patients were enrolled in our study. By the end of MP treatment, the proportion of patients who gained total or major (visual analog scale [VAS] score decreased by 50% or more) allodynia relief from the treatment was 91.18%, and a decrease in spontaneous pain was also observed. Moreover, this study showed MP could significantly improve the QoL of patients based on McGill Pain Questionnaire Short Form and EuroQol Five Dimensions Questionnaire. Four patients (11.76%) during MP treatment experienced mild or moderate side effects. None of the patients manifested CCS-associated neuropathic pain recurrence and MP-associated side effects at follow-up.

Conclusion

The current results suggested that MP offered an effective therapeutic alternative for relieving CCS-associated acute neuropathic pain with allodynia. Given the encouraging results of this study, it would be worthwhile to confirm these results in randomized placebo-controlled clinical trials.

Executive summary of the Clinical Guidelines of Pharmacotherapy for Neuropathic Pain: second edition by the Japanese Society of Pain Clinicians

Neuropathic pain has a substantial effect on quality of life (QOL). The Japanese Society of Pain Clinicians (JSPC) has developed clinical guidelines of pharmacotherapy for neuropathic pain. These guidelines offer clarity on recommendations based on both the most recent scientific evidence and expert opinions. Understanding the concept, disease entity, and burden of neuropathic pain, as well as its screening and diagnosis are important steps before starting pharmacotherapy. As well as other guidelines, the guidelines propose several lines of pharmacotherapies in a step-wise manner. To name a few different points, our guidelines propose an extract from inflamed cutaneous tissue of rabbits inoculated with vaccinia virus, which has been found to be effective for post-herpetic neuralgia in Japan, as one of the second-line drugs. When prescribing opioid analgesics, proposed as the third-line drugs, for neuropathic pain, the guidelines recommend physicians continue evaluations on either abuse or addiction. The guidelines do not recommend concomitant use of nonsteroidal anti-inflammatory drugs and acetaminophen because of lack of clinical evidence of their efficacy. If patients do not respond well to pharmacotherapy, which is prescribed in a step-wise manner, other treatment strategies should be considered to improve patients’ activities of daily living and QOL.

Drug therapy for chronic idiopathic axonal polyneuropathy

BACKGROUND

Chronic idiopathic axonal polyneuropathy (CIAP) is an insidiously progressive sensory or sensorimotor polyneuropathy that affects elderly people. Although severe disability or handicap does not occur, CIAP reduces quality of life. CIAP is diagnosed in 10% to 25% of people referred for evaluation of polyneuropathy. There is a need to gather and review emerging evidence on treatments, as the number of people affected is likely to increase in ageing populations. This is an update of a review first published in 2004 and previously updated in 2006, 2008, 2011 and 2013.

OBJECTIVES

To assess the effects of drug therapy for chronic idiopathic axonal polyneuropathy for reducing disability and ameliorating neurological symptoms and associated impairments, and to assess any adverse effects of treatment.

SEARCH METHODS

In July 2016, we searched Cochrane Central Register of Controlled Trials and the Cochrane Database of Systematic Reviews in the Cochrane Library, MEDLINE, Embase, and the Web of Science. We searched two trials registries for ongoing trials. We also handsearched the reference lists of relevant articles, reviews and textbooks identified electronically, and we would have contacted authors and other experts in the field to identify additional studies if this seemed useful.

SELECTION CRITERIA

We sought all randomised or quasi-randomised (alternate or other systematic treatment allocation) trials that examined the effects of any drug therapy in people with CIAP at least one year after the onset of treatment. People with CIAP had to fulfil the following criteria: age 40 years or older, distal sensory or sensorimotor polyneuropathy, absence of systemic or other neurological disease, chronic clinical course not reaching a nadir in less than two months, exclusion of any recognised cause of the polyneuropathy by medical history taking, clinical or laboratory investigations, and electrophysiological studies in agreement with axonal polyneuropathy, without evidence of demyelinating features. The primary outcome was the proportion of participants with a significant improvement in disability. Secondary outcomes were change in the mean disability score, change in the proportion of participants who make use of walking aids, change in the mean Medical Research Council sum score, degree of pain relief and/or reduction of other positive sensory symptoms, change in the proportion of participants with pain or other positive sensory symptoms, and frequency of adverse effects.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed the results of the literature search and extracted details of trial methodology and outcome data of all potentially relevant trials.

MAIN RESULTS

We identified 39 studies and assessed them for possible inclusion in the review, but we excluded all of them because of insufficient quality or lack of relevance. We summarised evidence from non-randomised studies in the Discussion.

AUTHORS' CONCLUSIONS

Even though CIAP has been clearly described and delineated, no adequate randomised or quasi-randomised controlled clinical treatment trials have been performed. In their absence there is no proven efficacious drug therapy.

A novel model of combined neuropathic and inflammatory pain displaying long-lasting allodynia and spontaneous pain-like behaviour

Many clinical cases of chronic pain exhibit both neuropathic and inflammatory components. In contrast, most animal models of chronic pain focus on one type of injury alone. Here we present a novel combined model of both neuropathic and inflammatory pain and characterise its distinctive properties. This combined model of chronic constriction injury (CCI) and intraplantar Complete Freund's Adjuvant (CFA) injection results in enhanced mechanical allodynia, thermal hyperalgesia, a static weight bearing deficit, and notably pronounced spontaneous foot lifting (SFL) behaviour (which under our conditions was not seen in either individual model and may reflect ongoing/spontaneous pain). Dorsal root ganglion (DRG) expression of Activating Transcription Factor-3 (ATF-3), a marker of axonal injury, was no greater in the combined model than CCI alone. Initial pharmacological characterisation of the new model showed that the SFL was reversed by gabapentin or diclofenac, typical analgesics for neuropathic or inflammatory pain respectively, but not by mexiletine, a Na(+) channel blocker effective in both neuropathic and inflammatory pain models. Static weight bearing deficit was moderately reduced by gabapentin, whereas only diclofenac reversed mechanical allodynia. This novel animal model of chronic pain may prove a useful test-bed for further analysing the pharmacological susceptibility of complicated clinical pain states.

Suppressive effects of glycyrrhetinic acid derivatives on tachykinin receptor activation and hyperalgesia

Glycyrrhetinic acid (GA), an aglycone of glycyrrhizin, isolated from the licorice root (Glycyrrhizia), and its semi-synthetic derivatives have a wide range of pharmacological effects. To investigate whether GA derivatives may be used as a new class of analgesics, we examined the effects of these compounds on human tachykinin receptors expressed in CHO-K1 cells. Among the GA derivatives examined, the disodium salt of olean-11,13(18)-dien-3β,30-O-dihemiphthalate inhibited the mobilization of [Ca(2+)](i) induced by substance P, neurokinin A, and neurokinin B in CHO-K1 cells expressing the human NK(1), NK(2), and NK(3) tachykinin receptors, respectively. In an inflammatory pain model, Compound 5 suppressed the capsaicin-induced flinching behavior in a dose-dependent manner. Compound 5 was also effective in suppressing pain-related behaviors in the late phase of the formalin test and reducing thermal hyperalgesia in the neuropathic pain state caused by sciatic nerve injury. Collectively, Compound 5 may be an analgesic candidate via tachykinin receptor antagonism.

Treatment considerations in neuropathic pain

Neuropathy is a relatively common source of acute and chronic pain. Emerging evidence suggests several pathophysiological mechanisms underlying the neuropathic pain associated with various disorders. Antidepressants and anticonvulsants have largely been the mainstay of treatment. Pharmacologic treatment of neuropathy frequently requires use of multiple medications. Ideally, the selection of which medications to use should be based on targeting the multiple pathophysiologic mechanisms contributing to neuropathic pain transmission. Psychological variables may play a role in predisposing patients to chronic neuropathy after acute illness. In addition, comorbid conditions, especially depression, can complicate the presentation, clinical course, and response to treatment of patients with chronic pain. Treatment of depression may be essential to fully enlist the chronic neuropathic pain patient in comprehensive pain management and rehabilitative approaches.

Antinociceptive effect of ambroxol in rats with neuropathic spinal cord injury pain

Symptoms of neuropathic spinal cord injury (SCI) pain include evoked cutaneous hypersensitivity and spontaneous pain, which can be present below the level of the injury. Adverse side-effects obtained with currently available analgesics complicate effective pain management in SCI patients. Voltage-gated Na(+) channels expressed in primary afferent nociceptors have been identified to mediate persistent hyperexcitability in dorsal root ganglia (DRG) neurons, which in part underlies the symptoms of nerve injury-induced pain. Ambroxol has previously demonstrated antinociceptive effects in rat chronic pain models and has also shown to potently block Na(+) channel current in DRG neurons. Ambroxol was tested in rats that underwent a mid-thoracic spinal cord compression injury. Injured rats demonstrated robust hind paw (below-level) heat and mechanical hypersensitivity. Orally administered ambroxol significantly attenuated below-level hypersensitivity at doses that did not affect performance on the rotarod test. Intrathecal injection of ambroxol did not ameliorate below-level hypersensitivity. The current data suggest that ambroxol could be effective for clinical neuropathic SCI pain. Furthermore, the data suggest that peripherally expressed Na(+) channels could lend themselves as targets for the development of pharmacotherapies for SCI pain.

Intravenous lidocaine and mexiletine in the management of trigeminal autonomic cephalalgias

Lidocaine and mexiletine are class 1B antiarrhythmic drugs that act on sodium channels. Lidocaine is also an important anesthetic and topical agent that is useful in the treatment of multiple pain disorders, and mexiletine is commonly used for neuropathic pain and myotonia. Both intravenous lidocaine and mexiletine are increasingly used to treat pain syndromes and appear to be particularly effective in neuropathic pain. This suggests a role for these agents in patients with headache disorders. This article describes the role of intravenous lidocaine and mexiletine in the management of headache and trigeminal autonomic cephalalgias based on the published literature to date and provides practical guidelines for their use.

Sodium channel blockers for the treatment of neuropathic pain

Drugs that block voltage-gated sodium channels are efficacious in the management of neuropathic pain. Accordingly, this class of ion channels has been a major focus of analgesic research both in academia and in the pharmaceutical/biotechnology industry. In this article, we review the history of the use of sodium channel blockers, describe the current status of sodium channel drug discovery, highlight the challenges and hurdles to attain sodium channel subtype selectivity, and review the potential usefulness of selective sodium channel blockers in neuropathic pain.

Morphine versus mexiletine for treatment of postamputation pain: a randomized, placebo-controlled, crossover trial

BACKGROUND

Stump and phantom pains are debilitating sequelae of amputations that are often resistant to treatment. The efficacy of pharmacologic therapies, including opioids and sodium channel blockers, for postamputation pain is uncertain.

METHODS

The authors conducted a double-blind, randomized, placebo-controlled, crossover study in adult patients with postamputation pain of 6 months or longer and greater than 3 on a 0-10 numeric pain rating scale. Each of the three treatment periods (morphine, mexiletine, or placebo) included a 1-week drug-free interval followed by 4-week titration, 2-week maintenance, and 2-week drug-taper phases. The primary outcome measure was change in average pain intensity from the drug-free baseline to the last week of maintenance.

RESULTS

Sixty amputees were enrolled; data were analyzed from 56 subjects for one drug period, 45 subjects for two drug periods, and 35 subjects who completed all three drug periods. The mean morphine and mexiletine dosages were 112 and 933 mg, respectively. Morphine treatment provided lower pain scores compared with placebo and mexiletine (P = 0.0003). The mean percent pain relief during treatment with placebo, mexiletine, and morphine was 19, 30, and 53%, respectively (P < 0.0001, morphine vs. placebo and mexiletine). The numbers needed to treat to obtain 50% and 33% decreases in pain intensity with morphine were 5.6 and 4.5, respectively. Treatment with morphine was associated with a higher rate of side effects.

CONCLUSIONS

Therapy with morphine, but not mexiletine, resulted in a decrease in intensity of postamputation pain but was associated with a higher rate of side effects and no improvement in self-reported levels of overall functional activity and pain-related interference in daily activities.

EFNS guidelines on pharmacological treatment of neuropathic pain

Neuropathic pain treatment remains unsatisfactory despite a substantial increase in the number of trials. This EFNS Task Force aimed at evaluating the existing evidence about the pharmacological treatment of neuropathic pain. Studies were identified using first the Cochrane Database then Medline. Trials were classified according to the aetiological condition. All class I and II controlled trials (according to EFNS classification of evidence) were assessed, but lower-class studies were considered in conditions that had no top level studies. Only treatments feasible in an outpatient setting were evaluated. Effects on pain symptoms/signs, quality of life and comorbidities were particularly searched for. Most of the randomized controlled trials included patients with postherpetic neuralgia (PHN) and painful polyneuropathies (PPN) mainly caused by diabetes. These trials provide level A evidence for the efficacy of tricyclic antidepressants, gabapentin, pregabalin and opioids, with a large number of class I trials, followed by topical lidocaine (in PHN) and the newer antidepressants venlafaxine and duloxetine (in PPN). A small number of controlled trials were performed in central pain, trigeminal neuralgia, other peripheral neuropathic pain states and multiple-aetiology neuropathic pains. The main peripheral pain conditions respond similarly well to tricyclic antidepressants, gabapentin, and pregabalin, but some conditions, such as HIV-associated polyneuropathy, are more refractory. There are too few studies on central pain, combination therapy, and head-to-head comparison. For future trials, we recommend to assess quality of life and pain symptoms or signs with standardized tools.

The pharmacotherapy of chronic pain: a review

The past two decades have contributed a large body of preclinical work that has assisted in our understanding of the underlying pathophysiological mechanisms that cause chronic pain. In this context, it has been recognized that effective treatment of pain is a priority and that treatment often involves the use of one or a combination of agents with analgesic action. The current review presents an evidence-based approach to the pharmacotherapy of chronic pain. Medline searches were done for all agents used as conventional treatment in chronic pain. Published papers up to June 2005 were included. The search strategy included randomized, controlled trials, and where available, systematic reviews and meta-analyses. Further references were found in reference sections of papers located using the above search strategy. Agents for which there were no controlled trials supporting efficacy in treatment of chronic pain were not included in the present review, except in cases where preclinical science was compelling, or where initial human work has been positive and where it was thought the reader would be interested in the scientific evidence to date.

[Neuropathic pain: experimental advances and clinical applications]

Neuropathic pain is a clinical entity designating the different types of pain associated with a lesion of the nervous system including a wide range of pathological conditions from painful peripheral lesions (for example diabetic neuropathy, post-zoster pain, trauma-induced nerve injury) and central pain (particularly stroke-induced pain, spinal lesions, and multiple sclerosis). Despite this wide range of etiologies, neuropathic pain has well characterized clinical features which generally allow distinction from other types of pain: continuous often burn-like pain, paroxysmal pain (electrical discharge, knife stab), evoked pain, highly invalidating pain (allodynia, hyperalgesia), and associated dysethesia and/or paresthesia. Over the last ten Years, very little work has been published on neuropathic pain, which is now becoming a very active domain of research in neurobiology. Advances to date have not been spectacular although better tolerated agents have been recently marketed. Future progress should enable an appropriate response to the therapeutic challenge of neuropathic pain.

EFNS guidelines on neuropathic pain assessment

In September 2001, a Task Force was set up under the auspices of the European Federation of Neurological Societies with the aim of evaluating the existing evidence about the methods of assessing neuropathic pain and its treatments. This review led to the development of guidelines to be used in the management of patients with neuropathic pain. In the clinical setting a neurological examination that includes an accurate sensory examination is often sufficient to reach a diagnosis. Nerve conduction studies and somatosensory-evoked potentials, which do not assess small fibre function, may demonstrate and localize a peripheral or central nervous lesion. A quantitative assessment of the nociceptive pathways is provided by quantitative sensory testing and laser-evoked potentials. To evaluate treatment efficacy in a patient and in controlled trials, the simplest psychometric scales and quality of life measures are probably the best methods. A laboratory measure of pain that by-passes the subjective report, and thus cognitive influences, is a hopeful aim for the future.

Mexiletine and Persistent Ophthalmic Changes

Mexilitine is an anti-arrhythmic agent used to treat neuropathic pain. The drug has a low side-effect profile with gastritis as the predominant complaint. The following two cases suggest that mexilitine can potentially cause persistent ophthalmic changes and should be used with caution in chronic pain patients with preexisting ocular disease.