Topiramate in painful diabetic polyneuropathy: findings from three double-blind placebo-controlled trials

Topiramate affords neuroprotection in diabetic neuropathy model via downregulating spinal GFAP/inflammatory burden and improving neurofilament production

The current study aimed to test the neuroprotective action of topiramate in mouse peripheral diabetic neuropathy (DN) and explored some mechanisms underlying this action. Mice were assigned as vehicle group, DN group, DN + topiramate 10-mg/kg and DN + topiramate 30-mg/kg. Mice were tested for allodynia and hyperalgesia and then spinal cord and sciatic nerves specimens were examined microscopically and neurofilament heavy chain (NEFH) immunostaining was performed. Results indicated that DN mice had lower the hotplate latency time (0.46-fold of latency to licking) and lower von-Frey test pain threshold (0.6-fold of filament size) while treatment with topiramate increased these values significantly. Sciatic nerves from DN control mice showed axonal degeneration while spinal cords showed elevated GFAP (5.6-fold) and inflammatory cytokines (∼3- to 4-fold) but lower plasticity as indicated by GAP-43 (0.25-fold). Topiramate produced neuroprotection and suppressed spinal cord GFAP/inflammation but enhanced GAP-43. This study reinforces topiramate as neuroprotection and explained some mechanisms included in alleviating neuropathy.

The Treatment of Painful Diabetic Neuropathy

Painful diabetic peripheral neuropathy (painful-DPN) is a highly prevalent and disabling condition, affecting up to one-third of patients with diabetes. This condition can have a profound impact resulting in a poor quality of life, disruption of employment, impaired sleep, and poor mental health with an excess of depression and anxiety. The management of painful-DPN poses a great challenge. Unfortunately, currently there are no Food and Drug Administration (USA) approved disease-modifying treatments for diabetic peripheral neuropathy (DPN) as trials of putative pathogenetic treatments have failed at phase 3 clinical trial stage. Therefore, the focus of managing painful- DPN other than improving glycaemic control and cardiovascular risk factor modification is treating symptoms. The recommended treatments based on expert international consensus for painful- DPN have remained essentially unchanged for the last decade. Both the serotonin re-uptake inhibitor (SNRI) duloxetine and α2δ ligand pregabalin have the most robust evidence for treating painful-DPN. The weak opioids (e.g. tapentadol and tramadol, both of which have an SNRI effect), tricyclic antidepressants such as amitriptyline and α2δ ligand gabapentin are also widely recommended and prescribed agents. Opioids (except tramadol and tapentadol), should be prescribed with caution in view of the lack of definitive data surrounding efficacy, concerns surrounding addiction and adverse events. Recently, emerging therapies have gained local licenses, including the α2δ ligand mirogabalin (Japan) and the high dose 8% capsaicin patch (FDA and Europe). The management of refractory painful-DPN is difficult; specialist pain services may offer off-label therapies (e.g. botulinum toxin, intravenous lidocaine and spinal cord stimulation), although there is limited clinical trial evidence supporting their use. Additionally, despite combination therapy being commonly used clinically, there is little evidence supporting this practise. There is a need for further clinical trials to assess novel therapeutic agents, optimal combination therapy and existing agents to determine which are the most effective for the treatment of painful-DPN. This article reviews the evidence for the treatment of painful-DPN, including emerging treatment strategies such as novel compounds and stratification of patients according to individual characteristics (e.g. pain phenotype, neuroimaging and genotype) to improve treatment responses.

Diabetic neuropathy: an insight on the transition from synthetic drugs to herbal therapies

The global pandemic of prediabetes and diabetes has led to a severe corresponding complication of these disorders. Neuropathy is one of the most prevalent complication of diabetes is, affecting blood supply of the peripheral nervous system that may eventually results into loss of sensations, injuries, diabetic foot and death. The utmost identified risk of diabetic neuropathy is uncontrolled high blood glucose levels. However, aging, body mass index (BMI), oxidative stress, inflammation, increased HbA1c levels and blood pressure are among the other key factors involved in the upsurge of this disease. The so far treatment to deal with diabetic neuropathy is controlling metabolic glucose levels. Apart from this, drugs like reactive oxygen species (ROS) inhibitors, aldose reductase inhibitors, PKC inhibitors, Serotonin-norepinephrine reuptake inhibitors (SNRIs), anticonvulsants, N-methyl-D-aspartate receptor (NMDAR) antagonists, are the other prescribed medications. However, the related side-effects (hallucinations, drowsiness, memory deficits), cost, poor pharmacokinetics and drug resistance brought the trust of patients down and thus herbal renaissance is occurring all over the word as the people have shifted their intentions from synthetic drugs to herbal remedies. Medicinal plants have widely been utilized as herbal remedies against number of ailments in Indian medicinal history. Their bioactive components are very much potent to handle different chronic disorders and complications with lesser-known side effects. Therefore, the current article mainly concludes the etiology and pathophysiology of diabetic neuropathy. Furthermore, it also highlights the important roles of medicinal plants and their naturally occurring bioactive compounds in addressing this disease.

Pharmacological Management of Painful Peripheral Neuropathies: A Systematic Review

Introduction

Peripheral neuropathic pain (PNP) arises either acutely or in the chronic phase of a lesion or disease of the peripheral nervous system and is associated with a notable disease burden. The management of PNP is often challenging. The aim of this systematic review was to evaluate current evidence, derived from randomized controlled trials (RCTs) that have assessed pharmacological interventions for the treatment of PNP due to polyneuropathy (PN).

Methods

A systematic search of the PubMed database led to the identification of 538 papers, of which 457 were excluded due to not meeting the eligibility criteria, and two articles were identified through screening of the reference lists of the 81 eligible studies. Ultimately, 83 papers were included in this systematic review.

Results

The best available evidence for the management of painful diabetic polyneuropathy (DPN) is for amitriptyline, duloxetine, gabapentin, pregabalin and venlafaxine as monotherapies and oxycodone as add-on therapy (level II of evidence). Tramadol appears to be effective when used as a monotherapy and add-on therapy in patients with PN of various etiologies (level II of evidence). Weaker evidence (level III) is available on the effectiveness of several other agents discussed in this review for the management of PNP due to PN.

Discussion

Response to treatment may be affected by the underlying pathophysiological mechanisms that are involved in the pathogenesis of the PN and, therefore, it is very important to thoroughly investigate patients presenting with PNP to determine the causes of this neuropathy. Future RCTs should be conducted to shed more light on the use of pharmacological approaches in patients with other forms of PNP and to design specific treatment algorithms.

Electronic supplementary material

The online version of this article (10.1007/s40122-020-00210-3) contains supplementary material, which is available to authorized users.

Diabetic Peripheral Neuropathy: Diagnosis and Treatment

BACKGROUND

Diabetic peripheral neuropathy (DPN) is traditionally divided into large and small fibre neuropathy (SFN). Damage to the large fibres can be detected using nerve conduction studies (NCS) and often results in a significant reduction in sensitivity and loss of protective sensation, while damage to the small fibres is hard to reliably detect and can be either asymptomatic, associated with insensitivity to noxious stimuli, or often manifests itself as intractable neuropathic pain.

OBJECTIVE

To describe the recent advances in both detection, grading, and treatment of DPN as well as the accompanying neuropathic pain.

METHODS

A review of relevant, peer-reviewed, English literature from MEDLINE, EMBASE and Cochrane Library between January 1st 1967 and January 1st 2020 was used.

RESULTS

We identified more than three hundred studies on methods for detecting and grading DPN, and more than eighty randomised-controlled trials for treating painful diabetic neuropathy.

CONCLUSION

NCS remains the method of choice for detecting LFN in people with diabetes, while a gold standard for the detection of SFN is yet to be internationally accepted. In the recent years, several methods with huge potential for detecting and grading this condition have become available including skin biopsies and corneal confocal microscopy, which in the future could represent reliable endpoints for clinical studies. While several newer methods for detecting SFN have been developed, no new drugs have been accepted for treating neuropathic pain in people with diabetes. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors and anticonvulsants remain first line treatment, while newer agents targeting the proposed pathophysiology of DPN are being developed.

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

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

Mirogabalin and emerging therapies for diabetic neuropathy

There are currently no approved disease-modifying therapies for diabetic neuropathy, and there are only 3 US Food and Drug Administration-approved therapies (pregabalin, duloxetine, and tapentadol) for painful diabetic neuropathy. They each have moderate efficacy with adverse effects limiting optimal dose titration. There is a considerable need for new therapies for the management of painful diabetic neuropathy. We reviewed the potential role of mirogabalin, which like gabapentin and pregabalin modulates the alpha-2/delta-1 subunit of the voltage-gated calcium channel, allowing the influx of calcium and release of neurotransmitters at the synaptic cleft in the central nervous system and spinal cord. It has shown efficacy and good tolerability in a Phase II study in diabetic painful neuropathy and based on the results of two Phase III clinical trials in diabetic painful neuropathy and post-herpetic neuralgia, Daiichi Sankyo submitted a marketing application for neuropathic pain in Japan in February 2018. We have also reviewed potential new therapies, currently in Phase II clinical trials that may modify disease and/or relieve neuropathic pain through novel modes of action.

Alternatives to Opioids in the Pharmacologic Management of Chronic Pain Syndromes: A Narrative Review of Randomized, Controlled, and Blinded Clinical Trials

Chronic pain exerts a tremendous burden on individuals and societies. If one views chronic pain as a single disease entity, then it is the most common and costly medical condition. At present, medical professionals who treat patients in chronic pain are recommended to provide comprehensive and multidisciplinary treatments, which may include pharmacotherapy. Many providers use nonopioid medications to treat chronic pain; however, for some patients, opioid analgesics are the exclusive treatment of chronic pain. However, there is currently an epidemic of opioid use in the United States, and recent guidelines from the Centers for Disease Control (CDC) have recommended that the use of opioids for nonmalignant chronic pain be used only in certain circumstances. The goal of this review was to report the current body of evidence-based medicine gained from prospective, randomized-controlled, blinded studies on the use of nonopioid analgesics for the most common noncancer chronic pain conditions. A total of 9566 studies were obtained during literature searches, and 271 of these met inclusion for this review. Overall, while many nonopioid analgesics have been found to be effective in reducing pain for many chronic pain conditions, it is evident that the number of high-quality studies is lacking, and the effect sizes noted in many studies are not considered to be clinically significant despite statistical significance. More research is needed to determine effective and mechanism-based treatments for the chronic pain syndromes discussed in this review. Utilization of rigorous and homogeneous research methodology would likely allow for better consistency and reproducibility, which is of utmost importance in guiding evidence-based care.

Pain phenotype as a predictor for drug response in painful polyneuropathy-a retrospective analysis of data from controlled clinical trials

The drugs available for treatment of neuropathic pain have somewhat disappointing efficacy with many patients left with limited or no effect. Individualized treatment based on phenotype according to presumed underlying pain mechanism(s) has been proposed to improve outcomes. We report a retrospective analysis of phenotype-specific effects of several neuropathic pain drugs, which were studied in a series of crossover, placebo-controlled, clinical trials. The data originate from 7 trials with similar design and outcome recordings, which all had a thorough baseline registration of symptoms, signs, and quantitative sensory testing. The latter was used to phenotype patients into subgroups reflecting presumed pain mechanisms. There were a total of 361 patient records distributed over treatments with 4 antidepressants and 4 anticonvulsants. Five of the drugs reduced total pain significantly compared with placebo. Only a few phenotype-specific differences in total pain reduction were found within the investigated drugs. Thus, imipramine reduced total pain 1.84 (CI: 0.02-3.67) and pregabalin 0.81 (CI: -0.67 to 2.29) in patients with than without gain of sensory function. Pregabalin showed a better effect in patients with preserved large fiber function with a mean difference in total pain reduction 1.31 (CI: 0.15-2.47). No phenotype-specific effects were found for venlafaxine, escitalopram, oxcarbazepine, valproic acid, levetiracetam, or St. John's wort. Thus, this post hoc analysis of 8 drugs with mainly nonselective actions on neuropathic pain mechanisms found limited usefulness of sensory phenotyping in pain as the basis for individualized treatment.

Efficacy and Safety of Pregabalin in the Treatment of Patients With Painful Diabetic Peripheral Neuropathy and Pain on Walking

OBJECTIVES

This randomized, double-blind, placebo-controlled, multicenter, 2-period crossover study (two 6-week treatment periods separated by a 2-week washout period) evaluated the efficacy and safety of pregabalin (150 to 300 mg/d) for treatment of pain and pain on walking in patients with painful diabetic peripheral neuropathy (DPN) who experienced pain while walking.

METHODS

Co-primary efficacy endpoints were: (1) mean pain score (last 7 daily pain diary scores, 0 to 10 numeric rating scale at end of each treatment period) and (2) DPN pain on walking (0 to 10 numeric rating scale immediately after walking 50 feet [15.2 m] on flat surface). Secondary endpoints included other pain parameters, patient-reported sleep, health-related quality of life, and safety measures.

RESULTS

Two hundred three patients were treated (pregabalin, n=198; placebo, n=186), with no statistically significant treatment difference for pregabalin versus placebo in the co-primary efficacy endpoints, mean DPN pain (P=0.0656) and mean DPN pain on walking (P=0.412). A carryover effect was observed. Analysis of co-primary endpoints for period 1 showed significant treatment difference for DPN pain (P=0.034) and DPN pain on walking (P=0.001). Treatment with pregabalin resulted in significant improvements versus placebo on prespecified patient global impression of change (end of period 1; P=0.002), and sleep interference rating scale (end of period 2; P=0.011). Adverse events were more frequent with pregabalin than with placebo and caused discontinuation in 13 (6.6%) pregabalin patients versus 5 (2.7%) placebo patients.

DISCUSSION

Failure to meet the co-primary objectives may be related to carryover effect from period 1 to period 2, lower pregabalin dose (150 to 300 mg/d), and/or placebo response in painful DPN.

Orofacial Pain: Pharmacologic Paradigms for Therapeutic Intervention

Pain is a universal experience with profound effects on the physiology, psychology, and sociology of the population. Orofacial pain (OFP) conditions are especially prevalent and can be severely debilitating to a patient's health-related quality of life. Evidence-based clinical trials suggest that pharmacologic therapy may significantly improve patient outcomes either alone or when used as part of a comprehensive treatment plan for OFP. The aim of this article is to provide therapeutic options from a pharmacologic perspective to treat a broad spectrum of OFP. Clinical-based systemic and topical applied pharmaceutical approaches are presented to treat the most common OFP syndromes.

Pharmacologic Management of Upper Extremity Chronic Nerve Pain

The treatment of pain is a complex process that requires a team approach. This article provides an overview of the pharmaceutical treatments available. It gives providers treating upper extremity disorders more tools to treat their patients with chronic pain. Another goal is to improve hand providers' understanding of the medications their pain colleagues prescribe in shared patients. Pharmaceuticals are an important component in the treatment of chronic pain and opioids are often not a good solution. Knowing what other medications are available can improve the care for these challenging patients.

Burning through the pain: treatments for diabetic neuropathy

The rise in the global burden of diabetes is spurring an increase in the prevalence of its complications. Diabetic peripheral neuropathy (DPN) is a common and devastating complication of diabetes, with multiple clinical manifestations. The most common is a symmetrical length-dependent dysfunction and damage of peripheral nerves. The management of DPN rests on three tenets: intensive glycaemic control, even though the evidence of benefit is questionable in people with type 2 diabetes; pathogenetic therapies; and symptomatic treatment. A number of pathogenetic treatments have been evaluated in phase III clinical trials, including α-lipoic acid (stems reactive oxygen species formation), benfotiamine (prevents vascular damage) and aldose-reductase inhibitors (reduce flux through the polyol pathway), protein kinase C inhibitors (prevent hyperglycaemia-induced activation of protein kinase C), nerve growth factors (stimulate nerve regeneration) and Actovegin® (improves tissue glucose and oxygen uptake). However, none have gained US Food and Drug Administration or European Medicines Agency (EMA) approval, questioning the validity of current trial designs and the endpoints deployed to define efficacy. For painful diabetic neuropathy, clinical guidelines recommend: atypical analgesics for pain relief, including duloxetine and amitriptyline; the γ-aminobutyric acid analogues gabapentin and pregabalin; opioids, including Tapentadol; and topical agents such as lidocaine and capsaicin. No single effective treatment exists for painful DPN, highlighting a growing need for studies to evaluate more potent and targeted drugs, as well as combinations. A number of novel potential candidates, including erythropoietin analogues and angiotensin II type 2 receptor anatagonists are currently being evaluated in phase II clinical trials.

Treating Diabetic Neuropathy: Present Strategies and Emerging Solutions

Diabetic peripheral neuropathies (DPN) are a heterogeneous group of disorders caused by neuronal dysfunction in patients with diabetes. They have differing clinical courses, distributions, fiber involvement (large or small), and pathophysiology. These complications are associated with increased morbidity, distress, and healthcare costs. Approximately 50% of patients with diabetes develop peripheral neuropathy, and the projected rise in the global burden of diabetes is spurring an increase in neuropathy. Distal symmetrical polyneuropathy (DSPN) with painful diabetic neuropathy, occurring in around 20% of diabetes patients, and diabetic autonomic neuropathy (DAN) are the most common manifestations of DPN. Optimal glucose control represents the only broadly accepted therapeutic option though evidence of its benefit in type 2 diabetes is unclear. A number of symptomatic treatments are recommended in clinical guidelines for the management of painful DPN, including antidepressants such as amitriptyline and duloxetine, the γ-aminobutyric acid analogues gabapentin and pregabalin, opioids, and topical agents such as capsaicin. However, monotherapy is frequently not effective in achieving complete resolution of pain in DPN. There is a growing need for head-to-head studies of different single-drug and combination pharmacotherapies. Due to the ubiquity of autonomic innervation in the body, DAN causes a plethora of symptoms and signs affecting cardiovascular, urogenital, gastrointestinal, pupillomotor, thermoregulatory, and sudomotor systems. The current treatment of DAN is largely symptomatic, and does not correct the underlying autonomic nerve deficit. A number of novel potential candidates, including erythropoietin analogues, angiotensin II receptor type 2 antagonists, and sodium channel blockers are currently being evaluated in phase II clinical trials.

Predictors of placebo response in peripheral neuropathic pain: insights from pregabalin clinical trials

Background

Greater understanding of factors associated with the high placebo-response rates noted in recent neuropathic pain trials may improve trial design. This study investigated placebo response and its predictors in pregabalin trials in patients with diabetic peripheral neuropathy (DPN) or postherpetic neuralgia.

Patients and methods

Individual patient data from 16 randomized, placebo-controlled, double-blind trials of pregabalin in 3,053 patients with DPN and 1,460 patients with postherpetic neuralgia were pooled (by condition and all together) in order to investigate the placebo response and its predictors. Univariate and multivariate analyses were performed across all 16 trials to identify predictors of change in pain score in patients. Trials with a >2-point mean reduction in pain score at endpoint with placebo were designated high placebo response and were compared with low placebo-response trials (those with a ≤2-point mean reduction) with respect to patient and study characteristics.

Results

Three high placebo-response studies were identified, with all in DPN patients and all conducted postapproval of pregabalin. Younger age, higher mean baseline pain score, longer study duration, higher ratio of patients on active treatment to placebo, and study conducted postapproval were all significantly associated with a higher placebo response (P<0.05). There was a trend towards an increased placebo response in all studies over time without any corresponding change in the response to pregabalin.

Conclusion

Consideration of the factors identified here as contributing to a higher placebo response could help improve the sensitivity and accuracy of clinical trials in patients with neuropathic pain.

Treatment of painful diabetic neuropathy

Painful diabetic neuropathy (PDN) is a debilitating consequence of diabetes that may be present in as many as one in five patients with diabetes. The objective assessment of PDN is difficult, making it challenging to diagnose and assess in both clinical practice and clinical trials. No single treatment exists to prevent or reverse neuropathic changes or to provide total pain relief. Treatment of PDN is based on three major approaches: intensive glycaemic control and risk factor management, treatments based on pathogenetic mechanisms, and symptomatic pain management. Clinical guidelines recommend pain relief in PDN through the use of antidepressants such as amitriptyline and duloxetine, the γ-aminobutyric acid analogues gabapentin and pregabalin, opioids and topical agents such as capsaicin. Of these medications, duloxetine and pregabalin were approved by the US Food and Drug Administration (FDA) in 2004 and tapentadol extended release was approved in 2012 for the treatment of PDN. Proposed pathogenetic treatments include α-lipoic acid (stems reactive oxygen species formation), benfotiamine (prevents vascular damage in diabetes) and aldose-reductase inhibitors (reduces flux through the polyol pathway). There is a growing need for studies to evaluate the most potent drugs or combinations for the management of PDN to maximize pain relief and improve quality of life. A number of agents are potential candidates for future use in PDN therapy, including Nav 1.7 antagonists, N-type calcium channel blockers, NGF antibodies and angiotensin II type 2 receptor antagonists.

Update on neuropathic pain treatment: ion channel blockers and gabapentinoids

Neuropathic pain is a debilitating chronic pain condition, which remains difficult to treat. The current mainstays of treatment include physical therapy, interventional procedures and medications. Among medications, ion channel blockers and gabapentinoids are the 2 classes of drugs commonly used to treat neuropathic pain. It has been suggested that these medications may be useful to treat a variety of neuropathic pain conditions. This article provides several updates on the utility of both ion channel blockers and gabapentinoids for the treatment of neuropathic pain.

New approaches to the pharmacotherapy of neuropathic pain

Pain is one of the most debilitating symptoms that presents with neuropathy. Neuropathic pain syndrome is a challenge to treat and, even with appropriate evidence-based treatment, only a 40% reduction of symptoms can be achieved in approximately half of patients. Furthermore, efficient doses are often difficult to obtain because of adverse effects. These observations underline that the treatment of neuropathic pain is still an unmet medical need. New approaches to the pharmacotherapy of neuropathy embrace different lines of work, including a fundamental mechanism-based approach, a clinical mechanism-based approach and an evidence-based approach. Moreover, interindividual variability in drug response, and genetic polymorphism in particular, is an emerging aspect to consider. Together with reviewing recent evidence-based guidelines as well as briefly discussing genetic polymorphisms that may influence the individual responses to treatments, this article will focus on what a mechanism-based approach is bringing to the clinical setting, on the perspective in fundamental research and on the difficulty of bridging the gap between fundamental notions and positive clinical outcomes.

Topiramate for the treatment of epilepsy and other nervous system disorders

Initially synthesized as an oral hypoglycemic agent, topiramate was approved for use as an anticonvulsant in 1996. Its broad spectrum efficacy in epilepsy, including as monotherapy and in children, is well established. Topiramate has also been used in the management of nonepileptic neurologic and psychiatric conditions, including migraine prophylaxis (with firmly established efficacy), obesity (with some evidence of long-term maintenance of weight loss), substance dependence, bipolar disorder and neuropathic pain, and it has been investigated as a possible neuroprotective agent. Paresthesias and cognitive side effects are the most common troublesome adverse effects. Recent trends towards lower doses may help achieve the best combination of efficacy and tolerability.

Topiramate for neuropathic pain and fibromyalgia in adults

BACKGROUND

Topiramate is an antiepileptic drug with multiple possible mechanisms of action. Antiepileptic drugs are widely used to treat chronic neuropathic pain (pain due to nerve damage) and fibromyalgia, and many guidelines recommend them.

OBJECTIVES

To assess the analgesic efficacy and associated adverse events of topiramate for chronic neuropathic pain and fibromyalgia in adults (aged 18 years and above).

SEARCH METHODS

On 8 May 2013, we searched the Cochrane Neuromuscular Disease Group Specialized Register, CENTRAL, MEDLINE, and EMBASE. We reviewed the bibliographies of all randomised trials identified and review articles, and also searched two clinical trial databases, ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform, to identify additional published or unpublished data.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) with double-blind assessment of participant outcomes following two weeks of treatment or longer (though the emphasis of the review was on studies of eight weeks or longer) that used a placebo or active comparator.

DATA COLLECTION AND ANALYSIS

We extracted efficacy and adverse event data, and two study authors examined issues of study quality independently. We performed analysis using two tiers of evidence. The first tier used data where studies reported the outcome of at least 50% pain reduction from baseline, lasted at least eight weeks, had a parallel group design, included 200 or more participants in the comparison, and reported an intention-to-treat analysis. First tier studies did not use last-observation-carried-forward (LOCF) or other imputation methods for dropouts. The second tier used data that failed to meet this standard; second tier results were therefore subject to potential bias.

MAIN RESULTS

We included four studies with 1684 participants. Three parallel-group placebo comparisons were in painful diabetic neuropathy (1643 participants), and one cross-over study with diphenhydramine as an active placebo (41 participants) was in lumbar radiculopathy. Doses of topiramate were titrated up to 200 mg/day or 400 mg/day. All studies had one or more sources of potential major bias, as they either used LOCF imputation or were of small size.No study provided first tier evidence for an efficacy outcome. There was no convincing evidence for efficacy of topiramate at 200 to 400 mg/day over placebo.Eighty-two per cent of participants taking topiramate 200 to 400 mg/day experienced at least one adverse event, as did 71% with placebo, and the number needed to treat for an additional harmful effect (NNTH) was 8.6 (95% confidence interval (CI) 4.9 to 35). There was no difference in serious adverse events recorded (6.6% versus 7.5%). Adverse event withdrawals with 400 mg daily were much more common with topiramate (27%) than with placebo (8%), with an NNTH of 5.4 (95% CI 4.3 to 7.1). Lack of efficacy withdrawal was less frequent with topiramate (12%) than placebo (18%). Weight loss was a common event in most studies. No deaths attributable to treatment were reported.

AUTHORS' CONCLUSIONS

Topiramate is without evidence of efficacy in diabetic neuropathic pain, the only neuropathic condition in which it has been adequately tested. The data we have includes the likelihood of major bias due to LOCF imputation, where adverse event withdrawals are much higher with active treatment than placebo control. Despite the strong potential for bias, no difference in efficacy between topiramate and placebo was apparent.

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.

Treatment of painful peripheral neuropathy

Neuropathic pain management is an important aspect in the management of painful peripheral neuropathy. Anticonvulsants and antidepressants have been studied extensively and are often used as first-line agents in the management of neuropathic pain. In this article, data from multiple randomized controlled studies on painful peripheral neuropathies are summarized to guide physicians in treating neuropathic pain. Treatment is a challenge given the diverse mechanisms of pain and variable responses in individuals. However, most patients derive pain relief from a well-chosen monotherapy or well-designed polypharmacy that combines agents with different mechanisms of action.

Painful diabetic polyneuropathy: approach to diagnosis and management

OBJECTIVES

To provide a current overview of the diagnostic work-up and management of painful diabetic polyneuropathy (PDPN).

METHODS

A review covering the literature from 2004 to 2011, which describes the tools designed to diagnose neuropathic pain and assess its severity, including self-administered questionnaires, validated laboratory tests and simple handheld screening devices, and the evidence-based therapeutic approaches to PDPN.

RESULTS

The clinical aspects, pathogenesis, and comorbidities of PDPN, as well as its impact on health related quality of life (HR-QoL), are the main drivers for the management of patients with suspected PDPN. PDPN treatment consists first of all in improving glycemic control and lifestyle intervention. A number of symptomatic pharmacological agents are available for pain control: tricyclic antidepressants and selective serotonin norepinephrine reuptake inhibitors (venlafaxine and duloxetine), α2-delta ligands (gabapentin and pregabalin), opioid analgesics (tramadol and oxycodone), and agents for topical use, such as lidocaine patch and capsaicin cream. With the exception of transcutaneous electrical nerve stimulation, physical treatment is not supported by adequate evidence.

DISCUSSION

As efficacy and tolerability of current therapy for PDPN are not ideal, the need for a better approach in management further exists. Novel compounds should be developed for the treatment of PDPN.

Management of painful neuropathies

Neuropathic pain is the most common type of pain in neuropathy. In painful polyneuropathies the pain usually has a "glove and stocking" distribution. The pain may be predominantly spontaneous, e.g., with a burning, pricking, or shooting character or characterized by evoked pain such as mechanical or cold allodynia. In the clinical setting, the prevention of painful neuropathies and treatment of underlying neuropathy remains inadequate and thus symptomatic treatment of the pain and related disability needs to be offered. Most randomized, double-blind, placebo-controlled trials (RCTs) published in painful neuropathy have been conducted in patients with diabetes and to what extent a treatment which is found effective in painful diabetic polyneuropathy can be expected to relieve other conditions like chemotherapy- or HIV-induced neuropathy is unknown. Tricyclic antidepressants (TCAs), gabapentin, pregabalin, and serotonin noradrenaline reuptake inhibitors (SNRIs) are first drug choices. In patients with localized neuropathic pain, a topical lidocaine patch may also be considered. Second-line treatments are tramadol and other opioids. New types of treatment include botulinum toxin type A (BTX-A), high-dose capsaicin patches, and cannabinoids. Other types of anticonvulsant drugs such as lamotrigine, oxcarbazepine, and lacosamide have a more questionable efficacy in painful polyneuropathy but may have an effect in a subgroup of patients. Combination therapy may be considered in patients with insufficient effect from one drug. Treatment is usually a trial-and-error process and has to be individualized to the single patient, taking into account all comorbidities such as possible concomitant depression, anxiety, diseases, and drug interactions. Side-effects to antidepressants include dry mouth, nausea, constipation, orthostatic hypotension, and sedation. ECG should always be obtained prior to treatment with TCAs, which also should not be used in patients with cardiac incompensation and epilepsy. The most common side-effects of gabapentin and pregabalin are CNS-related side-effects with dizziness and somnolence. Peripheral edema, weight gain, nausea, vertigo, asthenia, dry mouth, and ataxia may also occur. Topical treatments are better tolerated due to lack of systemic side-effects but there is still limited evidence for the long-term efficacy of these drugs. With available drugs, the average pain reduction is about 20-30%, and only 20-35% of the patients will achieve at least 50% pain reduction, which stresses the need of a multidisciplinary approach to pain treatment.

Diabetic neuropathies: diagnosis and management

INTRODUCTION

Changes in human behaviour and lifestyle over the last century have resulted in a dramatic increase in the incidence of diabetes worldwide. Neuropathy is a common and costly complication of both type 1 and type 2 diabetes. The prevalence of neuropathy is estimated to be about 8% in newly diagnosed patients and greater than 50% in patients with long-standing disease. There are two main types of diabetic neuropathies, named as sensorimotor and autonomic neuropathies. Sensorimotor neuropathy is marked by pain, paraesthesia and sensory loss, and autonomic neuropathy may contribute to myocardial infarction, malignant arrhythmia and sudden death.

METHODS

In this article we reviewed the pathogenesis, clinical manifestations diagnosis and treatment of diabetic neuropathies.

CONCLUSION

Sensorimotor and autonomic neuropathies (cardiovascular, gastrointestinal and genitourinary autonomic neuropathies) are common in diabetic patients. Apart from strict glycaemic control, no further therapeutic approach exists in the prevention of this phenomenon. Intensive diabetes therapy, intensive multifactorial cardiovascular risk reduction and lifestyle intervention are recommended in patients with cardiovascular autonomic neuropathy. Gastroparesis is the most debilitating complication of gastrointestinal autonomic neuropathy and genitourinary autonomic neuropathy can cause sexual dysfunction and neurogenic bladder; these conditions are hard to manage. The symptomatic treatment of sensory symptoms includes tricyclic antidepressants, serotonin and norepinephrine reuptake inhibitors, gabapentin, pregabalin and opioids. Other treatment strategies are not so effective.

Mechanisms of neuropathic pain

Neuropathic pain is a disease of global burden. Its symptoms include spontaneous and stimulus-evoked painful sensations. Several maladaptive mechanisms underlying these symptoms have been elucidated in recent years: peripheral sensitization of nociception, abnormal excitability of afferent neurons, central sensitization comprising pronociceptive facilitation, disinhibition of nociception and central reorganization processes, and sympathetically maintained pain. This review aims to illustrate these pathophysiological principles, focussing on molecular and neurophysiological findings. Finally therapeutic options based on these findings are discussed.

Update on the management of diabetic polyneuropathies

The prevalence of diabetic polyneuropathy (DPN) can approach 50% in subjects with longer-duration diabetes. The most common neuropathies are generalized symmetrical chronic sensorimotor polyneuropathy and autonomic neuropathy. It is important to recognize that 50% of subjects with DPN may have no symptoms and only careful clinical examination may reveal the diagnosis. DPN, especially painful diabetic peripheral neuropathy, is associated with poor quality of life. Although there is a better understanding of the pathophysiology of DPN and the mechanisms of pain, treatment remains challenging and is limited by variable efficacy and side effects of therapies. Intensification of glycemic control remains the cornerstone for the prevention or delay of DPN but optimization of other traditional cardiovascular risk factors may also be of benefit. The management of DPN relies on its early recognition and needs to be individually based on comorbidities and tolerability to medications. To date, most pharmacological strategies focus upon symptom control. In the management of pain, tricyclic antidepressants, selective serotonin noradrenaline reuptake inhibitors, and anticonvulsants alone or in combination are current first-line therapies followed by use of opiates. Topical agents may offer symptomatic relief in some patients. Disease-modifying agents are still in development and to date, antioxidant α-lipoic acid has shown the most promising effect. Further development and testing of therapies based upon improved understanding of the complex pathophysiology of this common and disabling complication is urgently required.

Pharmacological treatment of diabetic neuropathic pain

Neuropathic pain continues to be a difficult and challenging clinical issue to deal with effectively. Painful diabetic polyneuropathy is a complex pain condition that occurs with reasonable frequency in the population and it may be extremely difficult for clinicians to provide patients with effective analgesia. Chronic neuropathic pain may occur in approximately one of every four diabetic patients. The pain may be described as burning or a deep-seated ache with sporadic paroxysms of lancinating painful exacerbations. The pain is often constant, moderate to severe in intensity, usually primarily involves the feet and generally tends to worsen at night. Treatment may be multimodal but largely involves pharmacological approaches. Pharmacological therapeutic options include antidepressants (tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors), α2δ ligands and topical (5%) lidocaine patch. Other agents may be different antiepileptic drugs (carbamazepine, lamotrigine, topiramate), topical capsaicin, tramadol and other opioids. Progress continues with respect to understanding various mechanisms that may contribute to painful diabetic neuropathy. Agents that may hold some promise include neurotrophic factors, growth factors, immunomodulators, gene therapy and poly (adenosine diphosphate-ribose) polymerase inhibitors. It is hoped that in the future clinicians will be able to assess patient pathophysiology, which may help them to match optimal therapeutic agents to target individual patient aberrant mechanisms.

Adjuvant analgesics in cancer pain: a review

Adjuvant analgesics (co-analgesics) are medications whose primary indication is the management of a medical condition with secondary effects of analgesia. Cancer pain is multifactorial and often involves inflammatory, nociceptive, and neuropathic pain subtypes. Adjuvant analgesics used in conjunction with opioids have been found to be beneficial in the management of many cancer pain syndromes; however, they are currently underutilized. Antidepressants, anticonvulsants, local anesthetics, topical agents, steroids, bisphosphonates, and calcitonin are all adjuvants which have been shown to be effective in the management of cancer pain syndromes. When utilizing analgesic adjuvants in the treatment of cancer pain, providers must take into account the particular side effect profile of the medication. Ideally, adjuvant analgesics will be initiated at lower dosages and escalated as tolerated until efficacy or adverse effects are encountered.

Topiramate improves neurovascular function, epidermal nerve fiber morphology, and metabolism in patients with type 2 diabetes mellitus

PURPOSE

To assess the effects of topiramate on C-fiber function, nerve fiber morphology, and metabolism (including insulin sensitivity, obesity, and dyslipidemia) in type 2 diabetes.

PATIENTS AND METHODS

We conducted an 18-week, open-label trial treating patients with topiramate. Twenty subjects with type 2 diabetes and neuropathy (61.5 ± 1.29 years; 15 male, 5 female) were enrolled and completed the trial. Neuropathy was evaluated by total neuropathy scores, nerve conduction studies, quantitative sensory tests, laser Doppler skin blood flow, and intraepidermal nerve fibers in skin biopsies.

RESULTS

Topiramate treatment improved symptoms compatible with C-fiber dysfunction. Weight, blood pressure, and hemoglobin A(1c) also improved. Laser Doppler skin blood flow improved significantly after 12 weeks of treatment, but returned to baseline at 18 weeks. After 18 weeks of treatment there was a significant increase in intraepidermal nerve fiber length at the forearm, thigh, and proximal leg. Intraepidermal nerve fiber density was significantly increased by topiramate in the proximal leg.

CONCLUSION

This study is the first to demonstrate that it is possible to induce skin intraepidermal nerve fiber regeneration accompanied by enhancement of neurovascular function, translating into improved symptoms as well as sensory nerve function. The simultaneous improvement of selective metabolic indices may play a role in this effect, but this remains to be determined.

The evidence for pharmacological treatment of neuropathic pain

Randomized, double-blind, placebo-controlled trials on neuropathic pain treatment are accumulating, so an updated review of the available evidence is needed. Studies were identified using MEDLINE and EMBASE searches. Numbers needed to treat (NNT) and numbers needed to harm (NNH) values were used to compare the efficacy and safety of different treatments for a number of neuropathic pain conditions. One hundred and seventy-four studies were included, representing a 66% increase in published randomized, placebo-controlled trials in the last 5 years. Painful poly-neuropathy (most often due to diabetes) was examined in 69 studies, postherpetic neuralgia in 23, while peripheral nerve injury, central pain, HIV neuropathy, and trigeminal neuralgia were less often studied. Tricyclic antidepressants, serotonin noradrenaline reuptake inhibitors, the anticonvulsants gabapentin and pregabalin, and opioids are the drug classes for which there is the best evidence for a clinical relevant effect. Despite a 66% increase in published trials only a limited improvement of neuropathic pain treatment has been obtained. A large proportion of neuropathic pain patients are left with insufficient pain relief. This fact calls for other treatment options to target chronic neuropathic pain. Large-scale drug trials that aim to identify possible subgroups of patients who are likely to respond to specific drugs are needed to test the hypothesis that a mechanism-based classification may help improve treatment of the individual patients.

Efficacy and safety of lacosamide in painful diabetic neuropathy

OBJECTIVE

To evaluate efficacy and safety of lacosamide compared with placebo in painful diabetic polyneuropathy.

RESEARCH DESIGN AND METHODS

Diabetic patients with at least moderate neuropathic pain were randomized to placebo or lacosamide 400 (in a slow or standard titration) or 600 mg/day over 6-week titration and 12-week maintenance periods. Primary efficacy criterion was intra-individual change in average daily Numeric Pain Rating Scale score from baseline to the last 4 weeks.

RESULTS

For the primary end point, pain reduction was numerically but not statistically greater with lacosamide compared with placebo (400 mg/day, P = 0.12; 600 mg/day, P = 0.18). Both doses were significantly more effective compared with placebo over the titration (P = 0.03, P = 0.006), maintenance (P = 0.01, P = 0.005), and entire treatment periods (P = 0.03, P = 0.02). Safety profiles between titration schemes were similar.

CONCLUSIONS

Lacosamide reduced neuropathic pain and was well tolerated in diabetic patients, but the primary efficacy criterion was not met, possibly due to an increased placebo response over the last 4 weeks.

Research design considerations for confirmatory chronic pain clinical trials: IMMPACT recommendations

There has been an increase in the number of chronic pain clinical trials in which the treatments being evaluated did not differ significantly from placebo in the primary efficacy analyses despite previous research suggesting that efficacy could be expected. These findings could reflect a true lack of efficacy or methodological and other aspects of these trials that compromise the demonstration of efficacy. There is substantial variability among chronic pain clinical trials with respect to important research design considerations, and identifying and addressing any methodological weaknesses would enhance the likelihood of demonstrating the analgesic effects of new interventions. An IMMPACT consensus meeting was therefore convened to identify the critical research design considerations for confirmatory chronic pain trials and to make recommendations for their conduct. We present recommendations for the major components of confirmatory chronic pain clinical trials, including participant selection, trial phases and duration, treatment groups and dosing regimens, and types of trials. Increased attention to and research on the methodological aspects of confirmatory chronic pain clinical trials has the potential to enhance their assay sensitivity and ultimately provide more meaningful evaluations of treatments for chronic pain.

Recommendations for the pharmacological management of neuropathic pain: an overview and literature update

The Neuropathic Pain Special Interest Group of the International Association for the Study of Pain recently sponsored the development of evidence-based guidelines for the pharmacological treatment of neuropathic pain. Tricyclic antidepressants, dual reuptake inhibitors of serotonin and norepinephrine, calcium channel alpha(2)-delta ligands (ie, gabapentin and pregabalin), and topical lidocaine were recommended as first-line treatment options on the basis of the results of randomized clinical trials. Opioid analgesics and tramadol were recommended as second-line treatments that can be considered for first-line use in certain clinical circumstances. Results of several recent clinical trials have become available since the development of these guidelines. These studies have examined botulinum toxin, high-concentration capsaicin patch, lacosamide, selective serotonin reuptake inhibitors, and combination therapies in various neuropathic pain conditions. The increasing number of negative clinical trials of pharmacological treatments for neuropathic pain and ambiguities in the interpretation of these negative trials must also be considered in developing treatment guidelines. The objectives of the current article are to review the Neuropathic Pain Special Interest Group guidelines for the pharmacological management of neuropathic pain and to provide a brief overview of these recent studies.

[Objectivity in research in the pharmaceutical industry is possible]

A number of publications on publication bias or selected outcomes reporting have led critics to doubt that the pharmaceutical industry is able to remain objective in its research activities. This paper discusses the prerequisites for objective research and to what extent these are met by research projects conducted by the pharmaceutical industry. Problems with meeting objectivity criteria on the part of the pharmaceutical industry will be highlighted, distinguishing between industrial research activities themselves (i.e., studies) and the publication of data resulting from such research. The aim of the discussion is to illustrate how and which research-guiding conditions can ensure that sponsors indeed meet the criteria for objective research.