Dextromethorphan and quinidine in adult patients with uncontrolled painful diabetic peripheral neuropathy: a 29-day, multicenter, open-label, dose-escalation study

Painful diabetic neuropathy: The role of ion channels

Painful diabetic neuropathy (PDN) is a common chronic complication of diabetes that causes neuropathic pain and negatively affects the quality of life. The management of PDN is far from satisfactory. At present, interventions are primarily focused on symptomatic treatment. Ion channel disorders are a major cause of PDN, and a complete understanding of their roles and mechanisms may provide better options for the clinical treatment of PDN. Therefore, this review summarizes the important role of ion channels in PDN and the current drug development targeting these ion channels.

A Review on Mechanistic and Pharmacological Findings of Diabetic Peripheral Neuropathy including Pharmacotherapy

BACKGROUND

Chronic hyperglycemia and related complications involving peripheral nerves in diabetes are one of the most severe microvascular complications with an average prevalence of 50-60%. Diabetic neuropathy is among the vascular disorders of diabetes, the most debilitating and crippled, lethal condition impacting patients's quality of life.

METHODS

In the present review article, several hypotheses associated with the pathogenesis of Diabetic Peripheral Neuropathy (DPN) have been introduced, among them metabolic pathways associated with polyol pathway, oxidative stress, production of reactive oxygen species (ROS) amplified under chronic hyperglycemic conditions and activation of transcription factor Nuclear factor-κB (NF- κB). The review article also possesses pathogenetic and pharmacologic treatments along with others, including acupressure, lidocaine, and capsaicin for DPN.

CONCLUSION

It may be concluded that we can combat the pathogenesis of DPN with different suggested treatments.

Effectiveness of warm needling acupuncture for pain relief in patients with diabetic peripheral neuropathy: A protocol of systematic review

BACKGROUND

Warm needling acupuncture (WNA) has been widely utilized for pain management in patients with diabetic peripheral neuropathy (DPN). However, its results are still inconsistent, and no systematic review has specifically addressed this issue. Thus, this systematic review will comprehensively and systematically investigate the effectiveness and safety of WNA for pain relief in DPN.

METHODS

A comprehensive literature search of MEDLINE, EMBASE, Cochrane Library, Web of Science, Scopus, Allied and Complementary Medicine Database, CBM database, and China National Knowledge Infrastructure will be performed for randomized controlled trials that report WNA for pain relief in patients with DPN. All electronic databases will be searched from initial to the present without limitations of language and publication status. Two investigators will independently screen papers, collect data, and assess study quality. Cochrane risk of bias tool will be used for study quality assessment, and evidence quality will be evaluated using Grading of Recommendations Assessment, Development and Evaluations approach. RevMan 5.3 software will be applied for running statistical analysis.

RESULTS

This study will summarize the evidence for the effectiveness and safety of WNA for the management of pain in patients with DPN.

CONCLUSIONS

The findings of this study may provide helpful evidence to judge whether WNA for pain relief in DPN is effective or not.

State-of-the-art pharmacotherapy for diabetic neuropathy

INTRODUCTION

The global epidemic of diabetes has led to an epidemic of diabetes complications. Diabetic neuropathy is the most common microvascular complication, of which diabetic peripheral neuropathy (DPN) and autonomic neuropathy (AN) are the most prevalent, affecting ~50% of patients. DPN results in pain with a poor quality of life and a loss of sensation with an increased risk of foot ulceration. Autonomic neuropathy can cause significant morbidity in a minority and is associated with increased mortality. The cornerstone of treatment to prevent or limit the progression of DPN/AN is multifactorial risk factor modification including treatment of glycemia, lipids and blood pressure. Whilst, there are no FDA-approved disease-modifying therapies, there are a number of therapies to relieve symptoms in DPN and AN.

AREAS COVERED

The authors discuss current approved therapies for painful diabetic neuropathy and autonomic neuropathy. They also address the potential role of improving risk factors to limit the development and progression of diabetic neuropathy and new pathogenetic and pain-relieving treatments.

EXPERT OPINION

The FDA-approved Pregabalin and Duloxetine over 25 years ago and Tapentadol, 6 years ago for painful diabetic neuropathy. There are currently no FDA-approved disease-modifying treatments for diabetic neuropathy which has been attributed to inappropriate models of the disease with limited translational capacity and major limitations of trial designs and endpoints in clinical trials.

Antimalarial drugs and the prevalence of mental and neurological manifestations: A systematic review and meta-analysis

Background: Antimalarial drugs affect the central nervous system, but it is difficult to differentiate the effect of these drugs from that of the malaria illness. We conducted a systematic review to determine the association between anti-malarial drugs and mental and neurological impairment in humans.  Methods: We systematically searched online databases, including Medline/PubMed, PsychoInfo, and Embase, for articles published up to 14th July 2016. Pooled prevalence, heterogeneity and factors associated with prevalence of mental and neurological manifestations were determined using meta-analytic techniques.  Results: Of the 2,349 records identified in the initial search, 51 human studies met the eligibility criteria. The median pooled prevalence range of mental and neurological manifestations associated with antimalarial drugs ranged from 0.7% (dapsone) to 48.3% (minocycline) across all studies, while it ranged from 0.6% (pyrimethamine) to 42.7% (amodiaquine) during treatment of acute malaria, and 0.7% (primaquine/dapsone) to 55.0% (sulfadoxine) during prophylaxis. Pooled prevalence of mental and neurological manifestations across all studies was associated with an increased number of antimalarial drugs (prevalence ratio= 5.51 (95%CI, 1.05-29.04); P=0.045) in a meta-regression analysis. Headaches (15%) and dizziness (14%) were the most common mental and neurological manifestations across all studies. Of individual antimalarial drugs still on the market, mental and neurological manifestations were most common with the use of sulphadoxine (55%) for prophylaxis studies and amodiaquine (42.7%) for acute malaria studies. Mefloquine affected more domains of mental and neurological manifestations than any other antimalarial drug.  Conclusions: Antimalarial drugs, particularly those used for prophylaxis, may be associated with mental and neurological manifestations, and the number of antimalarial drugs taken determines the association. Mental and neurological manifestations should be assessed following the use of antimalarial drugs.

Antimalarial drugs and the prevalence of mental and neurological manifestations: A systematic review and meta-analysis

Background: Antimalarial drugs affect the central nervous system, but it is difficult to differentiate the effect of these drugs from that of the malaria illness. We conducted a systematic review to determine the association between anti-malarial drugs and mental and neurological impairment in humans.  Methods: We systematically searched online databases, including Medline/PubMed, PsychoInfo, and Embase, for articles published up to 14th July 2016. Pooled prevalence, heterogeneity and factors associated with prevalence of mental and neurological manifestations were determined using meta-analytic techniques.  Results: Of the 2,349 records identified in the initial search, 51 human studies met the eligibility criteria. The median pooled prevalence range of mental and neurological manifestations associated with antimalarial drugs ranged from 0.7% (dapsone) to 48.3% (minocycline) across all studies, while it ranged from 0.6% (pyrimethamine) to 42.7% (amodiaquine) during treatment of acute malaria, and 0.7% (primaquine/dapsone) to 55.0% (sulfadoxine) during prophylaxis. Pooled prevalence of mental and neurological manifestations across all studies was associated with an increased number of antimalarial drugs (prevalence ratio= 5.51 (95%CI, 1.05-29.04); P=0.045) in a meta-regression analysis. Headaches (15%) and dizziness (14%) were the most common mental and neurological manifestations across all studies. Of individual antimalarial drugs still on the market, mental and neurological manifestations were most common with the use of sulphadoxine (55%) for prophylaxis studies and amodiaquine (42.7%) for acute malaria studies. Mefloquine affected more domains of mental and neurological manifestations than any other antimalarial drug.  Conclusions: Antimalarial drugs, particularly those used for prophylaxis, may be associated with mental and neurological manifestations, and the number of antimalarial drugs taken determines the association. Mental and neurological manifestations should be assessed following the use of antimalarial drugs.

Rationale and design of a randomized double-blind clinical trial in breast cancer: dextromethorphan in chemotherapy-induced peripheral neuropathy

BACKGROUND

Anti-cancer chemotherapy often induces peripheral neuropathy and consequent cognitive and quality of life impairment. Guidelines recommend antiepileptics or antidepressants but their efficacy is limited.Dextromethorphan, a N-methyl-D-aspartate receptor antagonist, has shown its efficacy in painful diabetic neuropathy and in post-operative pain but has not been studied in chemotherapy-induced peripheral neuropathy. This clinical trial evaluates the effect of dextromethorphan on pain, cognition and quality of life in patients who suffer from neuropathic pain induced by chemotherapy for breast cancer. It also assesses the impact of dextromethorphan genetic polymorphism on analgesia.

METHODS AND DESIGN

This trial is a randomized, placebo-controlled, double-blind clinical study in two parallel groups (NCT02271893). It includes 40 breast cancer patients suffering from chemotherapy-induced peripheral neuropathy. They are randomly allocated to dextromethorphan (maximal dose 90 mg/day) or placebo for 4 weeks. The primary endpoint is pain intensity measured after 4 weeks of treatment on a (0-10) Numeric Pain Rating Scale. Secondary outcomes include assessment of neuropathic pain, cognitive function, anxiety/depression, sleep and quality of life. Data analysis is performed using mixed models and the tests are two-sided, with a type I error set at α=0.05.

DISCUSSION

Considering the poor efficacy of available drugs in chemotherapy-induced neuropathic pain, dextromethorphan may be a valuable therapeutic option. Pharmacogenetics may provide predictive factors of dextromethorphan response in patients suffering from breast cancer.

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.

Measuring health-related quality of life in diabetic peripheral neuropathy: a systematic review

We undertook a systematic review of disease-specific measures of health-related quality of life (HRQL) in diabetic peripheral neuropathy (DPN) to appraise the scientific (psychometric) evidence and make recommendations about the best instrument(s) to use. DPN is a common complication of diabetes mellitus. A need to consider the broad impact of DPN, rather than just pain and the increasingly recognised need to assess patient-reported outcomes such as HRQL in evaluating healthcare has led to a demand for rigorous outcome measures. To identify appropriate disease-specific measures, we searched four databases: PubMed, Embase, PsycINFO and CINAHL Plus. Data were extracted from each article using a standard data extraction form and the psychometric properties of each HRQL measure were reviewed. We identified three DPN-specific measures of HRQL: PN-QOL-97, Norfolk QOL-DN, NeuroQoL. All three measures satisfy at least one criterion for both reliability and validity, though all also have some disadvantages. Where there is no requirement for multi-language versions, the PN-QOL-97 is a useful instrument. Studies that involve multiple languages would need to use the shorter QOL-DN but would also need to incorporate complementary instruments to address the psychological and emotional impact of DPN.

Efficacy and safety of dextromethorphan/quinidine at two dosage levels for diabetic neuropathic pain: a double-blind, placebo-controlled, multicenter study

OBJECTIVE

To evaluate dextromethorphan coadministered with quinidine as treatment of diabetic peripheral neuropathic pain.

DESIGN

In a 13-week, phase 3, randomized controlled trial, 379 adults with daily symmetric diabetic peripheral neuropathy (DPN) leg pain for ≥3 months received double-blind placebo, dextromethorphan/quinidine (DMQ) 45/30 mg, or DMQ 30/30 mg, administered once daily for 7 days and twice daily thereafter. Efficacy measures included four pain rating scales applied daily using patient diaries, and another two applied at five clinic visits.

RESULTS

On all six scales, DMQ 45/30 mg was significantly superior to placebo, including the primary efficacy analysis, which utilized mixed-effects modeling to test all scores on an 11-point numerical Pain Rating Scale (P < 0.0001). Sensitivity analyses gave consistent results. Efficacy vs placebo was also seen for diary ratings of present pain intensity, and pain interference with sleep and with activities (all P < 0.0001). Among clinic visit assessments, DMQ 45/30 mg demonstrated greater leg pain relief (P = 0.0002) and greater reduction of leg pain intensity (P = 0.0286) vs placebo. The efficacy of DMQ 30/30 mg was numerically less than for 45/30 mg but for most outcomes remained significantly greater vs placebo. Adverse events were mostly mild or moderate and of expected types. Discontinuation for adverse events in the DMQ groups was at least twice as common as placebo.

CONCLUSIONS

Throughout a 13-week trial, DMQ was effective, with an acceptable safety profile, for treatment of DPN pain. Other fixed-dose combinations of DMQ should be studied to improve overall tolerability while maintaining significant efficacy.

Current approaches with the glutamatergic system as targets in the treatment of neuropathic pain

Glutamate is the most widely distributed and a major excitatory neurotransmitter in the CNS. It has been found to play a critical role in various physiological functions in which increased glutamate or its subsequent stimulation is thought to have a role in pathophysiological mechanism of various CNS diseases like epilepsy, stroke, depression and pain. Early attempts to develop glutamatergic antagonists failed in clinical studies due to nonselective or competitive antagonism and have a lot of safety issues like loss of cognitive functions, psychomimetic effect and sedation. Neuropathic pain can be described as pain associated with damage or permanent alteration of the peripheral or central nervous system. At present, there are very few effective therapies for neuropathic pain. The current approach includes targeting specific or alternate binding sites of glutamate receptors, resulting in reduced CNS liabilities. Targeting the glutamatergic system shows a better efficacy and fewer side effects, compared with classical drugs for the treatment of neuropathic pain. This review discusses the various targets on glutamatergic system, which includes the receptors, transporters and enzymes, for the treatment of neuropathic pain and their advantages over classical glutamatergic antagonists. The review also highlights the newer drugs in clinical trials for neuropathic pain.

Painful diabetic neuropathy: epidemiology, natural history, early diagnosis, and treatment options

OBJECTIVE

To facilitate the clinician's understanding of the basis and treatment of painful diabetic neuropathy (PDN).

BACKGROUND

PDN is one of several clinical syndromes in patients with diabetic peripheral neuropathy (DPN) and presents a major challenge for optimal management.

METHODS

A systematic review of the literature was undertaken for articles specific to PDN, using Medline databases between 1966 and 2007.

RESULTS

The epidemiology of PDN has not been well established and on the basis of available data the prevalence of pain is 10% to 20% in patients with diabetes and from 40% to 50% in those with diabetic neuropathy. It has a significant impact on the quality of life and health care costs. Pathophysiologic mechanisms underlying PDN are similar to other neuropathic pain disorders and are broadly characterized as peripheral and central sensitization. The natural course of PDN is variable, with many patients experiencing spontaneous improvement and resolution of pain. Hyperglycemia-induced pathways result in nerve dysfunction and damage, which lead to hyperexcitable peripheral and central pathways of pain. Glycemic control may prevent or partially reverse DPN and modulate PDN. Quantifying neuropathic pain is difficult, especially for clinical trials, although this has improved recently with the development of neuropathic pain-specific tools, such as the Neuropathic Pain Questionnaire and the Neuropathic Pain Symptom Inventory. Current therapeutic options are limited to symptomatic treatment and are similar to other types of neuropathic pain.

CONCLUSIONS

A better understanding of the peripheral and central mechanisms resulting in PDN is likely to promote the development of more targeted and effective treatment.

Management of painful diabetic neuropathy

The commonest cause of peripheral neuropathy is diabetes and pain occurs in approximately 30% of diabetic patients with neuropathy. It is extremely distressing for the patient and poses significant difficulties in management, as no treatment to date provides total relief and the side effects of therapy limit dose titration. Understanding the pathogenesis of diabetic neuropathy may lead to the development of new treatments for preventing nerve damage. Furthermore, a better understanding of the mechanisms that modulate pain may lead to more effective relief of painful symptoms. This review provides an update on the assessment and treatment of painful diabetic neuropathy.

Dextromethorphan and quinidine combination for heroin detoxification

Dextromethorphan (DM) is a low-affinity, non-competitive NMDA receptor antagonist that has shown promise in preclinical and preliminary clinical studies for the reduction of opioid withdrawal symptoms, but when used at higher doses, it is associated with deleterious side effects attributed to its metabolite, dextrorphan. A clinical trial was therefore conducted to test the withdrawal-suppressant effect of a combination of dextromethorphan with quinidine (DM/Q). Quinidine inhibits the metabolism of dextromethorphan, reducing dextrorphan levels. Opioid-dependent patients were admitted to an inpatient unit, stabilized for three days on morphine (25 mg, sc, every six hours), and randomly assigned on day 2 to DM/Q (30 mg/30 mg, twice a day) (n = 22) or matching placebo (n = 9) prior to the discontinuation of morphine on day 4. Withdrawal symptoms, measured with the Modified Himmelsbach Opioid Withdrawal Scale (MHOWS), increased significantly on days 4 and 5 (Z = 3.70, p = .0002), and by day 6, 90% of the sample (28/31) had dropped out of the study. There were no differences between treatment groups on either outcome measure. The combination of dextromethorphan and quinidine appears ineffective as a primary treatment for opioid withdrawal. Future studies should examine dextromethorphan as an adjunct to other anti-withdrawal medications and focus more on the relationship between dextrorphan levels and withdrawal suppression.