NMDA receptor blockade in chronic neuropathic pain: a comparison of ketamine and magnesium chloride

A Randomized, Double-Blind, Placebo-Controlled Trial to Evaluate the Therapeutic Effect of Magnesium-L-Threonate Supplementation for Persistent Pain After Breast Cancer Surgery

Purpose

Post-mastectomy pain syndrome is a common yet debilitating neuropathic complication after breast cancer procedures, resulting in significantly reduced quality of life. Recently, emerging evidence has supported the therapeutic effect of magnesium administration in chronic pain. However, the role of magnesium supplementation in development of chronic pain after breast cancer surgery remains less known. The aim of this study was to evaluate therapeutic effect of magnesium supplementation on persistent pain after breast cancer procedure.

Patients and Methods

This was a randomized, double-blind, placebo-controlled clinical trial. A total of 109 patients who underwent breast cancer procedure received magnesium-L-threonate (n = 48) or placebo (n = 61) for 12 weeks. Chronic pain incidence, short form of the McGill Pain Questionnaire (SF-MPQ), Generalized Anxiety Disorder Scale (GAD-7), Patient Health Questionnaire-9 (PHQ-9), Pittsburgh Sleep Quality Index (PSQI), and Telephone Interview for Cognitive Status (TICS) were evaluated at 3- and 6-month follow-up.

Results

About 31% (15 out of 48) of patients reported chronic pain after magnesium supplementation, and 26% (16 out of 61) of the control group at 6-month follow-up respectively. Total scores of SF-MPQ were significantly increased in the control group 6 months after surgical intervention (mean difference, 1.475; 95% CI, -2.730 to -0.2211), but NOT in the magnesium treated group (mean difference, 1.250; 95% CI, -2.775 to 0.2748). No significant differences were found between two cohorts on SF-MPQ, GAD-7, PHQ-9, PSQI, or TICS at each timepoint.

Conclusion

Oral supplementation of magnesium-L-threonate did not effectively prevent the development of persistent pain in breast cancer survivors, nor provide sufficient pain relief over placebo. We did not observe improvement of pain, mood, sleep disorder, or cognitive function after 12-week magnesium supplementation. Future study may focus on magnesium combined with other effective anti-neuropathic pain treatment.

Magnesium Sulfate Reduces Carrageenan-Induced Rat Paw Inflammatory Edema Via Nitric Oxide Production

Background

Magnesium is an antagonist of the N-methyl-D-aspartate receptor. This study aimed to investigate the anti-edematous effect of magnesium sulfate (MS) in different protocols of use and the possible mechanism of its action.

Methods

In a rat model of carrageenan-induced paw inflammation, the anti-edematous activity of MS was assessed with a plethysmometer. The effects of the nonselective inhibitor (L-NAME), selective inhibitor of neuronal (L-NPA) and inducible (SMT) nitric oxide synthase on the effects of MS were evaluated.

Results

MS administered systemically before or after inflammation reduced edema by 30% (5 mg/kg, P < .05) and 55% (30 mg/kg, P < .05). MS administered locally (.5 mg/paw, P < .05) significantly prevented the development of inflammatory edema by 60%. L-NAME, intraperitoneally administered before MS, potentiated (5 mg/kg, P < .05) or reduced (3 mg/kg, P < .05), while in the highest tested dose L-NPA (2 mg/kg, P < .01) and SMT (.015 mg/kg, P < .01) reduced the anti-edematous effect of MS.

Conclusions

Magnesium is a more effective anti-edematous drug in therapy than for preventing inflammatory edema. The effect of MS is achieved after systemic and local peripheral administration and when MS is administered as a single drug in a single dose. This effect is mediated at least in part via the production of nitric oxide.

Prevention, diagnosis, and treatment of opioid use disorder under the supervision of opioid stewardship programs: it's time to act now

The third opium war may have already started, not only due to illicit opioid trafficking from the Golden Crescent and Golden Triangle on the international front but also through indiscriminate opioid prescription and opioid diversion at home. Opioid use disorder (OUD), among unintentional injuries, has become one of the top 4 causes of death in the United States (U.S.). An OUD is defined as a problematic pattern of opioid use resulting in clinically significant impairment or distress, consisting of 2 or more of 11 problems within 1 year, as described by the Diagnostic and Statistical Manual for Mental Disorders, Fifth Edition. Observation of aberrant behaviors of OUD is also helpful for overworked clinicians. For the prevention of OUD, the Opioid Risk Tool and the Current Opioid Misuse Measure are appropriate screening tests before and during opioid administration, respectively. Treatment of OUD consists of 3 opioid-based U.S. Food and Drug Administration-approved medications, including methadone, buprenorphine, and naltrexone, and non-opioid-based symptomatic medications for reducing opioid withdrawal syndromes, such as α2 agonists, β-blockers, antidiarrheals, antiemetics, non-steroidal anti-inflammatory drugs, and benzodiazepines. There are at least 6 recommendable guidelines and essential terms related to OUD. Opioid stewardship programs are now critical to promoting appropriate use of opioid medications, improving patient outcomes, and reducing misuse of opioids, influenced by the successful implementation of antimicrobial stewardship programs. Despite the lack of previous motivation, now is the critical time for trying to reduce the risk of OUD.

NMDARs mediate peripheral and central sensitization contributing to chronic orofacial pain

Peripheral and central sensitizations of the trigeminal nervous system are the main mechanisms to promote the development and maintenance of chronic orofacial pain characterized by allodynia, hyperalgesia, and ectopic pain after trigeminal nerve injury or inflammation. Although the pathomechanisms of chronic orofacial pain are complex and not well known, sufficient clinical and preclinical evidence supports the contribution of the N-methyl-D-aspartate receptors (NMDARs, a subclass of ionotropic glutamate receptors) to the trigeminal nociceptive signal processing pathway under various pathological conditions. NMDARs not only have been implicated as a potential mediator of pain-related neuroplasticity in the peripheral nervous system (PNS) but also mediate excitatory synaptic transmission and synaptic plasticity in the central nervous system (CNS). In this review, we focus on the pivotal roles and mechanisms of NMDARs in the trigeminal nervous system under orofacial neuropathic and inflammatory pain. In particular, we summarize the types, components, and distribution of NMDARs in the trigeminal nervous system. Besides, we discuss the regulatory roles of neuron-nonneuronal cell/neuron-neuron communication mediated by NMDARs in the peripheral mechanisms of chronic orofacial pain following neuropathic injury and inflammation. Furthermore, we review the functional roles and mechanisms of NMDARs in the ascending and descending circuits under orofacial neuropathic and inflammatory pain conditions, which contribute to the central sensitization. These findings are not only relevant to understanding the underlying mechanisms, but also shed new light on the targeted therapy of chronic orofacial pain.

Mediators of Neuropathic Pain; Focus on Spinal Microglia, CSF-1, BDNF, CCL21, TNF-α, Wnt Ligands, and Interleukin 1β

Intractable neuropathic pain is a frequent consequence of nerve injury or disease. When peripheral nerves are injured, damaged axons undergo Wallerian degeneration. Schwann cells, mast cells, fibroblasts, keratinocytes and epithelial cells are activated leading to the generation of an “inflammatory soup” containing cytokines, chemokines and growth factors. These primary mediators sensitize sensory nerve endings, attract macrophages, neutrophils and lymphocytes, alter gene expression, promote post-translational modification of proteins, and alter ion channel function in primary afferent neurons. This leads to increased excitability and spontaneous activity and the generation of secondary mediators including colony stimulating factor 1 (CSF-1), chemokine C-C motif ligand 21 (CCL-21), Wnt3a, and Wnt5a. Release of these mediators from primary afferent neurons alters the properties of spinal microglial cells causing them to release tertiary mediators, in many situations via ATP-dependent mechanisms. Tertiary mediators such as BDNF, tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and other Wnt ligands facilitate the generation and transmission of nociceptive information by increasing excitatory glutamatergic transmission and attenuating inhibitory GABA and glycinergic transmission in the spinal dorsal horn. This review focusses on activation of microglia by secondary mediators, release of tertiary mediators from microglia and a description of their actions in the spinal dorsal horn. Attention is drawn to the substantial differences in the precise roles of various mediators in males compared to females. At least 25 different mediators have been identified but the similarity of their actions at sensory nerve endings, in the dorsal root ganglia and in the spinal cord means there is considerable redundancy in the available mechanisms. Despite this, behavioral studies show that interruption of the actions of any single mediator can relieve signs of pain in experimental animals. We draw attention this paradox. It is difficult to explain how inactivation of one mediator can relieve pain when so many parallel pathways are available.

Current Strategies for the Management of Painful Diabetic Neuropathy

The development of painful diabetic neuropathy (PDN) is a common complication of chronic diabetes that can be associated with significant disability and healthcare costs. Prompt symptom identification and aggressive glycemic control is essential in controlling the development of neuropathic complications; however, adequate pain relief remains challenging and there are considerable unmet needs in this patient population. Although guidelines have been established regarding the pharmacological management of PDN, pain control is inadequate or refractory in a high proportion of patients. Pharmacotherapy with anticonvulsants (pregabalin, gabapentin) and antidepressants (duloxetine) are common first-line agents. The use of oral opioids is associated with considerable morbidity and mortality and can also lead to opioid-induced hyperalgesia. Their use is therefore discouraged. There is an emerging role for neuromodulation treatment modalities including intrathecal drug delivery, spinal cord stimulation, and dorsal root ganglion stimulation. Furthermore, consideration of holistic alternative therapies such as yoga and acupuncture may augment a multidisciplinary treatment approach. This aim of this review is to focus on the current management strategies for the treatment of PDN, with a discussion of treatment rationale and practical considerations for their implementation.

Interactions between Ketamine and Magnesium for the Treatment of Pain: Current State of the Art

BACKGROUND

Over the past three decades, NMDA-receptor antagonists have been shown to be efficient drugs for treating pain, particularly pain resistant to conventional analgesics. Emphasis will be on the old-new drugs, ketamine and magnesium, and their combination as a novel approach for treating chronic pain.

METHODS

The MEDLINE database was searched via PubMed for articles that were published up to March 1, 2020, with the keywords 'ketamine', 'magnesium', and 'pain' (in the title/abstract).

RESULTS

Studies in animals, as well as humans, have shown that interactions of ketamine and magnesium can be additive, antagonistic, and synergistic. These discrepancies might be due to differences in magnesium and ketamine dosage, administration times, and the chronological order of drug administration. Different kinds of pain can also be the source of divergent results.

CONCLUSION

This review explains why studies performed with a combination of ketamine and magnesium have given inconsistent results. Because of the lack of efficacy of drugs available for pain, ketamine and magnesium in combination provide a novel therapeutic approach that needs to be standardized with a suitable dosing regimen, including the chronological order of drug administration.

Selenium reduces nociceptive response in acute 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced neurotoxicity

The potential of Se to alleviate pain associated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity was investigated.

Swiss mice were intraperitoneally injected with MPTP (20 mg/kg) 4 times with an interval of 2 h in 1 day. Seven days after MPTP injection, the mice (n = 5 mice per group) were randomly assigned to groups: MPTP-, DOPA (50 mg/kg)-, Se4 (0.4 mg/kg)-, Se6 (0.6 mg/kg)-, DOPA+Se4-, and DOPA+Se6-treated groups were compared with controls. MPTP mice were treated for seven days; thereafter, motor-coordination and nociceptive-motor reactions were assessed. Pro-inflammatory cytokines (IL-1β, IL-6 and TNFα), and selected pain biomarkers (substance P (SP), glutamate and β-endorphin) were assessed in the serum and the substantial nigra pars compacta (SNpc).

Motor activity was increased slightly by Se (0.6 or 0.4 mg/kg) vs. MPTP (10.48 ± 2.71 or 11.81 ± 1.28 s vs. 3.53 ± 0.06 s respectively) but considerably increased by DOPA (50 mg/kg) vs. MPTP (50.47 ± 3.06 s vs. 3.53 ± 0.06 s respectively). Se and DOPA increased nociceptive threshold but Se alone reduced both serum and SN pro-inflammatory cytokines. Se modulates SP while DOPA modulates SP and glutamate in the SNpc of mice treated with MPTP.

Se suppressed pro-inflammatory cytokines and restored the basal pain biomarkers in the SNpc of mice treated with MPTP. Se requires further study as analgesic adjuvant.

Nutritional Supplements for the Treatment of Neuropathic Pain

Neuropathic pain affects 7-10% of the population and is often ineffectively and incompletely treated. Although the gold standard for treatment of neuropathic pain includes tricyclic antidepressants (TCAs), serotonin-noradrenaline reuptake inhibitors, and anticonvulsants, patients suffering from neuropathic pain are increasingly turning to nonpharmacologic treatments, including nutritional supplements for analgesia. So-called "nutraceuticals" have garnered significant interest among patients seeking to self-treat their neuropathic pain with readily available supplements. The supplements most often used by patients include vitamins such as vitamin B and vitamin D, trace minerals zinc and magnesium, and herbal remedies such as curcumin and St. John's Wort. However, evidence surrounding the efficacy and mechanisms of these supplements in neuropathic pain is limited, and the scientific literature consists primarily of preclinical animal models, case studies, and small randomized controlled trials (RCTs). Further exploration into large randomized controlled trials is needed to fully inform patients and physicians on the utility of these supplements in neuropathic pain. In this review, we explore the basis behind using several nutritional supplements commonly used by patients with neuropathic pain seen in rheumatology clinics.

Magnesium for Pain Treatment in 2021? State of the Art

Background: Magnesium (Mg) is commonly used in clinical practice for acute and chronic pain and has been reported to reduce pain intensity and analgesics consumption in a number of studies. Results are, however, contested. Objectives: This review aims to investigate randomised clinical trials (RCTs) on the effectiveness of Mg treatment on pain and analgesics consumption in situations including post-operative pain, migraine, renal pain, chronic pain, neuropathic pain and fibromyalgia. Results: The literature search identified 81 RCTs (n = 5447 patients) on Mg treatment in pain (50 RCTs in post-operative pain, 18 RCTs in migraine, 5 RCTs in renal pain, 6 RCTs in chronic/neuropathic pain, 2 RCTs in fibromyalgia). Conclusion: The level of evidence for the efficacy of Mg in reducing pain and analgesics consumption is globally modest and studies are not very numerous in chronic pain. A number of gaps have been identified in the literature that need to be addressed especially in methodology, rheumatic disease, and cancer. Additional clinical trials are needed to achieve a sufficient level of evidence and to better optimize the use of Mg for pain and pain comorbidities in order to improve the quality of life of patients who are in pain.

Efficacy and Safety of Magnesium for the Management of Chronic Pain in Adults: A Systematic Review

Chronic pain is a highly prevalent and complex health problem that is associated with a heavy symptom burden, substantial economic and social impact, and also, very few highly effective treatments. This review examines evidence for the efficacy and safety of magnesium in chronic pain. The previously published protocol for this review was registered in International Prospective Register of Systematic Reviews (PROSPERO), MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials (CENTRAL) databases were searched until September 2018. We included randomized controlled trials (RCTs) comparing magnesium (at any dose, frequency, or route of administration) with placebo using participant-reported pain measures. A total of 9 RCTs containing 418 participants were included. Three studies examined neuropathic pain (62 participants), 3 examined migraines (190 participants), 2 examined complex regional pain syndrome (86 participants), and 1 examined low back pain with a neuropathic component (80 participants). Heterogeneity of included studies precluded any meta-analyses. No judgment could be made about safety because adverse events were inconsistently reported in the included studies. Evidence of analgesic efficacy from included studies was equivocal. However, reported efficacy signals in some of the included trials provide a rationale for more definitive studies. Future, larger-sized trials with good assay sensitivity and better safety assessment and reporting, as well as careful attention to formulations with optimal bioavailability, will serve to better define the role of magnesium in the management of chronic pain.

Magnesium and Pain

In terms of antinociceptive action, the main mode of action of magnesium involves its antagonist action at the N-methyl-d-aspartate (NMDA) receptor, which prevents central sensitization and attenuates preexisting pain hypersensitivity. Given the pivotal function of NMDA receptors in pain transduction, magnesium has been investigated in a variety of pain conditions. The oral and parenteral administration of magnesium via the intravenous, intrathecal, or epidural route may alleviate pain and perioperative anesthetic and analgesic requirements. These beneficial effects of magnesium therapy have also been reported in patients with neuropathic pain, such as malignancy-related neurologic symptoms, diabetic neuropathy, postherpetic neuralgia, and chemotherapy-induced peripheral neuropathy. In addition, magnesium treatment is reportedly able to alleviate fibromyalgia, dysmenorrhea, headaches, and acute migraine attacks. Although magnesium plays an evolving role in pain management, better understanding of the mechanism underlying its antinociceptive action and additional clinical studies is required to clarify its role as an adjuvant analgesic.

Normalization of magnesium deficiency attenuated mechanical allodynia, depressive-like behaviors, and memory deficits associated with cyclophosphamide-induced cystitis by inhibiting TNF-α/NF-κB signaling in female rats

Background

Bladder-related pain symptoms in patients with bladder pain syndrome/interstitial cystitis (BPS/IC) are often accompanied by depression and memory deficits. Magnesium deficiency contributes to neuroinflammation and is associated with pain, depression, and memory deficits. Neuroinflammation is involved in the mechanical allodynia of cyclophosphamide (CYP)-induced cystitis. Magnesium-L-Threonate (L-TAMS) supplementation can attenuate neuroinflammation. This study aimed to determine whether and how L-TAMS influences mechanical allodynia and accompanying depressive symptoms and memory deficits in CYP-induced cystitis.

Methods

Injection of CYP (50 mg/kg, intraperitoneally, every 3 days for 3 doses) was used to establish a rat model of BPS/IC. L-TAMS was administered in drinking water (604 mg·kg⁻¹·day⁻¹). Mechanical allodynia in the lower abdomen was assessed with von Frey filaments using the up-down method. Forced swim test (FST) and sucrose preference test (SPT) were used to measure depressive-like behaviors. Novel object recognition test (NORT) was used to detect short-term memory function. Concentrations of Mg²⁺ in serum and cerebrospinal fluid (CSF) were measured by calmagite chronometry. Western blot and immunofluorescence staining measured the expression of tumor necrosis factor-α/nuclear factor-κB (TNF-α/NF-κB), interleukin-1β (IL-1β), and N-methyl-d-aspartate receptor type 2B subunit (NR2B) of the N-methyl-d-aspartate receptor in the L6–S1 spinal dorsal horn (SDH) and hippocampus.

Results

Free Mg²⁺ was reduced in the serum and CSF of the CYP-induced cystitis rats on days 8, 12, and 20 after the first CYP injection. Magnesium deficiency in the serum and CSF correlated with the mechanical withdrawal threshold, depressive-like behaviors, and short-term memory deficits (STMD). Oral application of L-TAMS prevented magnesium deficiency and attenuated mechanical allodynia (n = 14) and normalized depressive-like behaviors (n = 10) and STMD (n = 10). The upregulation of TNF-α/NF-κB signaling and IL-1β in the L6–S1 SDH or hippocampus was reversed by L-TAMS. The change in NR2B expression in the SDH and hippocampus in the cystitis model was normalized by L-TAMS.

Conclusions

Normalization of magnesium deficiency by L-TAMS attenuated mechanical allodynia, depressive-like behaviors, and STMD in the CYP-induced cystitis model via inhibition of TNF-α/NF-κВ signaling and normalization of NR2B expression. Our study provides evidence that L-TAMS may have therapeutic value for treating pain and comorbid depression or memory deficits in BPS/IC patients.

Inhibition of Cytochrome P450 Side-Chain Cleavage Attenuates the Development of Mechanical Allodynia by Reducing Spinal D-Serine Production in a Murine Model of Neuropathic Pain

Research indicates that neurosteroids are locally synthesized in the central nervous system and play an important modulatory role in nociception. While the neurosteroidogenic enzyme, cytochrome P450 side-chain cleavage enzyme (P450scc), is the initiating enzyme of steroidogenesis, P450scc has not been examined under the pathophysiological conditions associated with peripheral neuropathy. Thus, we investigated whether chronic constriction injury (CCI) of the sciatic nerve increases the expression of P450scc in the spinal cord and whether this increase modulates serine racemase (Srr) expression and D-serine production contributing to the development of neuropathic pain. CCI increased the immunoreactivity of P450scc in astrocytes of the ipsilateral lumbar spinal cord dorsal horn. Intrathecal administration of the P450scc inhibitor, aminoglutethimide, during the induction phase of neuropathic pain (days 0 to 3 post-surgery) significantly suppressed the CCI-induced development of mechanical allodynia and thermal hyperalgesia, the increased expression of astrocyte Srr in both the total and cytosol levels, and the increases in D-serine immunoreactivity at day 3 post-surgery. By contrast, intrathecal administration of aminoglutethimide during the maintenance phase of pain (days 14 to 17 post-surgery) had no effect on the developed neuropathic pain nor the expression of spinal Srr and D-serine immunoreactivity at day 17 post-surgery. Intrathecal administration of exogenous D-serine during the induction phase of neuropathic pain (days 0 to 3 post-surgery) restored the development of mechanical allodynia, but not the thermal hyperalgesia, that were suppressed by aminoglutethimide administration. Collectively, these results demonstrate that spinal P450scc increases the expression of astrocyte Srr and D-serine production, ultimately contributing to the development of mechanical allodynia induced by peripheral nerve injury.

Low-dose ketamine provides poor analgesia for pain in redback spider envenoming

Redback spider envenoming causes severe pain lasting several days. A recent clinical trial found that antivenom is not effective. We investigated ketamine for pain in redback spider envenoming. Ten adult patients with severe pain from redback spider envenoming were administered 15 mg intravenous ketamine after standard analgesia, then up to 4 oral doses of ketamine 25- 50 mg. Three patients had a clinically significant improvement in pain compared to baseline after intravenous ketamine. Five patients had a minimal decrease in pain and 2 had no improvement. Eight patients received oral ketamine: 4 doses in 5 and 2 doses in 3. At 24 h, 3/6 patients assessed had clinically significant improvement in pain and 4/5 patients assessed at 48 h, had clinically significant improvement in pain. Six patients reported side effects, including dissociation (4) and hallucinations (2). Five patients required rescue opioids and 2 were readmitted to hospital. We found that ketamine provided no additional pain relief in redback spider envenoming, compared to standard analgesia, and resulted in unacceptable adverse effects.

A Systematic Review of NMDA Receptor Antagonists for Treatment of Neuropathic Pain in Clinical Practice

OBJECTIVE

To investigate the efficacy of N-methyl-D-aspartate receptor (NMDAR) antagonists for neuropathic pain (NeuP) and review literature to determine if specific pharmacologic agents provide adequate NeuP relief.

METHODS

Literature was reviewed on PubMed using a variety of key words for 8 NMDAR antagonists. These key words include: "Ketamine and Neuropathy," "Ketamine and Neuropathic Pain," "Methadone and Neuropathy," "Methadone and Neuropathic Pain," "Memantine and Neuropathic pain," "Memantine and Neuropathy," "Amantadine and Neuropathic Pain," "Amantadine and Neuropathy," "Dextromethorphan and Neuropathic Pain," "Dextromethorphan and Neuropathy," "Carbamazepine and Neuropathic Pain," "Carbamazepine and Neuropathy," "Valproic Acid and Neuropathy," "Valproic Acid and Neuropathic Pain," "Phenytoin and Neuropathy," and "Phenytoin and Neuropathic Pain." With the results, the papers were reviewed using the PRISMA (Preferred Reporting in Systematic and Meta-Analyses) guideline.

RESULTS

A total of 58 randomized controlled trials were reviewed among 8 pharmacologic agents, which are organized by date and alphabetical order. Of the trials for ketamine, 15 showed some benefit for analgesia. Methadone had 3 positive trials, while amantadine and memantine each only had 2 trials showing NeuP analgesic properties. Dextromethorphan and valproic acid both had 4 randomized controlled trials that showed some NeuP treatment benefit while carbamazepine had over 8 trials showing efficacy. Finally, phenytoin only had 1 trial that showed clinical response in treatment.

CONCLUSIONS

There are a variety of NMDAR antagonist agents that should be considered for treatment of NeuP. Nevertheless, continued and further investigation of the 8 pharmacologic agents is needed to continue to evaluate their efficacy for treatment of NeuP.

Expanding Role of NMDA Receptor Antagonists in the Management of Pain

Pain management is complex regardless of whether the pain is acute or chronic in nature or non-cancer or cancer related. In addition, relatively few pain pharmacotherapy options with adequate efficacy and safety data currently exist. Consequently, interest in the role of NMDA receptor antagonists as a pharmacological pain management strategy has surfaced. This narrative review provides an overview of the NMDA receptor and elaborates on the pharmacotherapeutic profile and pain management literature findings for the following NMDA receptor antagonists: ketamine, memantine, dextromethorphan, and magnesium. The literature on this topic is characterized by small studies, many of which exhibit methodological flaws. To date, ketamine is the most studied NMDA receptor antagonist for both acute and chronic pain management. Although further research about NMDA receptor antagonists for analgesia is needed and the optimal dosage/administration regimens for these drugs have yet to be determined, ketamine appears to hold the most promise and may be of particular value in the perioperative pain management realm.

Evaluation of Prophylactic and Therapeutic Effects of Tramadol and Tramadol Plus Magnesium Sulfate in an Acute Inflammatory Model of Pain and Edema in Rats

Background: Inflammatory pain is the most commonly treated clinical pain, since it develops following trauma or surgery, and accompanies rheumatic or arthritic diseases. Tramadol is one of the most frequently used opioid analgesics in acute and chronic pain of different origin. Magnesium is a widely used dietary supplement that was recently shown to be a safe analgesic drug in different models of inflammatory pain. Aim: This study aimed to evaluate the effects of systemically or locally injected tramadol with/without systemically injected magnesium sulfate in prophylactic or therapeutic protocols of application in a rat model of somatic inflammation. Methods: Inflammation of the rat hind paw was induced by an intraplantar injection of carrageenan (0.1 ml, 0.5%). The antihyperalgesic/antiedematous effects of tramadol (intraperitoneally or intraplantarly injected), and tramadol-magnesium sulfate (subcutaneously injected) combinations were assessed by measuring the changes in paw withdrawal thresholds or paw volume induced by carrageenan. The drugs were administered before or after inflammation induction. Results: Systemically administered tramadol (1.25-10 mg/kg) before or after induction of inflammation reduced mechanical hyperalgesia and edema with a maximal antihyperalgesic/antiedematous effect of about 40-100%. Locally applied tramadol (0.125 mg/paw) better reduced edema (50-100%) than pain (20-50%) during 24 h. Administration of a fixed dose of tramadol (1.25 mg/kg) with different doses of magnesium led to a dose-dependent enhancement and prolongation of the analgesic effect of tramadol both in prevention and treatment of inflammatory pain. Magnesium increases the antiedematous effect of tramadol in the prevention of inflammatory edema while reducing it in treatment. Conclusion: According to results obtained in this animal model, systemic administration of low doses of tramadol and magnesium sulfate given in combination is a potent, effective and relatively safe therapeutic option for prevention and especially therapy of somatic inflammatory pain. The best result is achieved when tramadol is combined with magnesium sulfate at a dose that is equivalent to the average human recommended daily dose and when the drugs are administered when inflammation is maximally developed.

Preventive effect of oral magnesium in postmastectomy pain: protocol for a randomised, double-blind, controlled clinical trial

INTRODUCTION

Breast cancer affects 1 in 10 women worldwide, and mastectomy is a cause of chronic pain with neuropathic characteristics. N-methyl-D-aspartate receptor (NMDAR) antagonists such as ketamine, memantine, dextromethorphan or magnesium are used to treat refractory pain by blocking NMDAR. Oral memantine has been shown to prevent postmastectomy pain and cognitive impact and to maintain quality of life. Likewise, the present study is intended to assess the preventive effect of oral magnesium, administered ahead of mastectomy, on the development of neuropathic pain. As a physiological blocker of NMDAR, magnesium could be an interesting candidate to prevent postoperative pain and associated comorbidities, including cognitive and emotional disorders, multiple analgesic consumption and impaired quality of life.

METHODS AND ANALYSIS

A randomised double-blind controlled clinical trial (NCT03063931) will include 100 women with breast cancer undergoing mastectomy at the Oncology Hospital, Clermont-Ferrand, France. Magnesium (100 mg/day; n=50) or placebo (n=50) will be administered for 6 weeks, starting 2 weeks before surgery. Intensity of pain, cognitive and emotional function and quality of life will be assessed by questionnaires. The primary endpoint is pain intensity on a 0-10 numerical rating scale at 1 month postmastectomy. Data analysis will use mixed models; all tests will be two-tailed, with type-I error set at α=0.05.

ETHICS AND DISSEMINATION

The study protocol and informed consent form were approved in December 2016 by the French Research Ethics Committee (South East VI Committee). Results will be communicated in various congresses and published in international publications.

TRIAL REGISTRATION NUMBER

NCT03063931.

Emerging Trends in Pain Medication Management: Back to the Future: A Focus on Ketamine

Providers face many challenges when faced with pain management. Pain is complex, difficult to understand and diagnose, and especially enigmatic to manage. The discovery of nonopioid agents for pain management has become particularly important considering the ongoing opioid epidemic. This review is focused on revisiting ketamine, an agent that has historically been used for anesthesia, in new ways to manage pain. Ketamine has unique pharmacologic properties that may prevent the development of pain as well as reduce chronic pain. This has led to the use of ketamine for perioperative analgesia as well as chronic pain syndromes. In select patients with pain refractory to other treatment modalities, ketamine may provide much needed relief.

Ketamine infusion therapy for chronic pain management in South Korea: A national survey for pain physicians with a narrative review

Although ketamine infusion therapy (KIT) has been used extensively for the treatment of chronic persistent pain, there remains high heterogeneity in the administration protocols. The aim of this study was to assess the current clinical use and the infusion protocols of KIT in South Korea and to compare the protocol details with previous relevant studies.In the first phase, an online survey about KIT, including protocol information, was distributed to pain physicians managing chronic pain patients at 47 teaching hospitals registered in the Korean Pain Society. In the second phase, a review of the KIT protocols in previous clinical studies was conducted and compared with the survey results.Among 47 institutions, 35 replied; among them, 25 institutions performed KIT on an outpatient basis. The administration protocol for KIT varied greatly among institutions: the total infusion dose of ketamine ranged from 3.5 to 140 mg/70 kg, with a mode of 70 mg [interquartile range (IQR): 62.0; 8.0-70.0 mg] administered in 1 to 3 hours. In 10 previous studies of outpatient KIT, the total dose of ketamine ranged from 12.6 to 98 mg/70 kg, with a mode of 35 mg [IQR: 40 mg; 23-63 mg] given in 1 to 4 hours, which was significantly lower than in our results (P = .01). In the survey, physicians listed hallucination as the most frequent side effect.Although KIT is used in Korean pain centers, there is wide variation regarding the specific infusion protocols. The total dose of ketamine used in South Korea is significantly higher than the general recommendations for outpatient management and may compromise patient safety. The results of this survey reinforce the need for specific guidelines for KIT in managing chronic pain that counterbalance its risks and benefits.

Consensus Guidelines on the Use of Intravenous Ketamine Infusions for Chronic Pain From the American Society of Regional Anesthesia and Pain Medicine, the American Academy of Pain Medicine, and the American Society of Anesthesiologists

BACKGROUND

Over the past 2 decades, the use of intravenous ketamine infusions as a treatment for chronic pain has increased dramatically, with wide variation in patient selection, dosing, and monitoring. This has led to a chorus of calls from various sources for the development of consensus guidelines.

METHODS

In November 2016, the charge for developing consensus guidelines was approved by the boards of directors of the American Society of Regional Anesthesia and Pain Medicine and, shortly thereafter, the American Academy of Pain Medicine. In late 2017, the completed document was sent to the American Society of Anesthesiologists' Committees on Pain Medicine and Standards and Practice Parameters, after which additional modifications were made. Panel members were selected by the committee chair and both boards of directors based on their expertise in evaluating clinical trials, past research experience, and clinical experience in developing protocols and treating patients with ketamine. Questions were developed and refined by the committee, and the groups responsible for addressing each question consisted of modules composed of 3 to 5 panel members in addition to the committee chair. Once a preliminary consensus was achieved, sections were sent to the entire panel, and further revisions were made. In addition to consensus guidelines, a comprehensive narrative review was performed, which formed part of the basis for guidelines.

RESULTS

Guidelines were prepared for the following areas: indications; contraindications; whether there was evidence for a dose-response relationship, or a minimum or therapeutic dose range; whether oral ketamine or another N-methyl-D-aspartate receptor antagonist was a reasonable treatment option as a follow-up to infusions; preinfusion testing requirements; settings and personnel necessary to administer and monitor treatment; the use of preemptive and rescue medications to address adverse effects; and what constitutes a positive treatment response. The group was able to reach consensus on all questions.

CONCLUSIONS

Evidence supports the use of ketamine for chronic pain, but the level of evidence varies by condition and dose range. Most studies evaluating the efficacy of ketamine were small and uncontrolled and were either unblinded or ineffectively blinded. Adverse effects were few and the rate of serious adverse effects was similar to placebo in most studies, with higher dosages and more frequent infusions associated with greater risks. Larger studies, evaluating a wider variety of conditions, are needed to better quantify efficacy, improve patient selection, refine the therapeutic dose range, determine the effectiveness of nonintravenous ketamine alternatives, and develop a greater understanding of the long-term risks of repeated treatments.

Effect of ketamine combined with magnesium sulfate in neuropathic pain patients (KETAPAIN): study protocol for a randomized controlled trial

Background

Neuropathic pain is difficult to treat, and the efficacy of recommended drugs remains limited. N-methyl-d-aspartate receptors are implicated, and antagonists are a pharmacological option. Ketamine is widely used in French pain clinics, but without consensus or recommendations. Furthermore, the association of ketamine with magnesium has been poorly studied. The aim of the present study is to evaluate the benefit of ketamine with or without magnesium in refractory neuropathic pain.

Methods/design

A randomized, double-blind, crossover, placebo-controlled study will be performed in Clermont-Ferrand University Hospital, Clermont-Ferrand, France. The aim is to evaluate the effect of ketamine with or without magnesium in 22 patients with neuropathic pain. Intravenous ketamine/placebo, ketamine/magnesium sulfate, or placebo/placebo will be administered consecutively to each patient, in random order, once at 5-week intervals. The primary endpoint is the AUC of pain intensity assessed on a 0–10 Numeric Pain Rating Scale for a 5-week period. Data analysis will be performed on an intention-to-treat basis, and all statistical tests (except primary analysis) will be performed with an α risk of 5% (two-sided).

Discussion

Considering the poor efficacy of the drugs available for neuropathic pain, ketamine with or without magnesium sulfate may be a valuable therapeutic option that needs to be standardized.

Trial registration

EudraCT number–2015-000142-29. Registered on April 9, 2015; version 1.4

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2254-3) contains supplementary material, which is available to authorized users.

Magnesium sulfate reduces formalin-induced orofacial pain in rats with normal magnesium serum levels

BACKGROUND

In humans, orofacial pain has a high prevalence and is often difficult to treat. Magnesium is an essential element in biological a system which controls the activity of many ion channels, neurotransmitters and enzymes. Magnesium produces an antinociceptive effect in neuropathic pain, while in inflammatory pain results are not consistent. We examined the effects of magnesium sulfate using the rat orofacial formalin test, a model of trigeminal pain.

METHODS

Male Wistar rats were injected with 1.5% formalin into the perinasal area, and the total time spent in pain-related behavior (face rubbing) was quantified. We also spectrophotometrically determined the concentration of magnesium and creatine kinase activity in blood serum.

RESULTS

Magnesium sulfate administered subcutaneously (0.005-45mg/kg) produced significant antinociception in the second phase of the orofacial formalin test in rats at physiological serum concentration of magnesium. The effect was not dose-dependent. The maximum antinociceptive effect of magnesium sulfate was about 50% and was achieved at doses of 15 and 45mg/kg. Magnesium did not affect increase the levels of serum creatine kinase activity.

CONCLUSIONS

Preemptive systemic administration of magnesium sulfate as the only drug can be used to prevent inflammatory pain in the orofacial region. Its analgesic effect is not associated with magnesium deficiency.

Syntheses, analytical and pharmacological characterizations of the 'legal high' 4-[1-(3-methoxyphenyl)cyclohexyl]morpholine (3-MeO-PCMo) and analogues

New psychoactive substances (NPS) are commonly referred to as 'research chemicals', 'designer drugs' or 'legal highs'. One NPS class is represented by dissociative anesthetics, which include analogues of the arylcyclohexylamine phencyclidine (PCP), ketamine and diphenidine. A recent addition to the NPS market was 4-[1-(3-methoxyphenyl)cyclohexyl]morpholine (3-MeO-PCMo), a morpholine analogue of 3-MeO-PCP. Although suspected to have dissociative effects in users, information about its pharmacological profile is not available. From clinical and forensic perspectives, detailed analytical data are needed for identification, especially when facing the presence of positional isomers, as these are frequently unavailable commercially. This study presents the analytical and pharmacological characterization of 3-MeO-PCMo along with five additional analogues, namely the 2- and 4-MeO-PCMo isomers, 3,4-methylenedioxy-PCMo (3,4-MD-PCMo), 3-Me-PCMo and PCMo. All six arylcyclohexylmorpholines were synthesized and characterized using chromatographic, mass spectrometric and spectroscopic techniques. The three positional isomers could be differentiated and the identity of 3-MeO-PCMo obtained from an internet vendor was verified. All six compounds were also evaluated for affinity at 46 central nervous system receptors including the N-methyl-d-aspartate receptor (NMDAR), an important target for dissociative anesthetics such as PCP and ketamine. In vitro binding studies using (+)-[3-³ H]-MK-801 in rat forebrain preparations revealed moderate affinity for NMDAR in the rank order of 3-Me >3-MeO > PCMo >3,4-MD > 2-MeO > 4-MeO-PCMo. 3-MeO-PCMo was found to have moderate affinity for NMDAR comparable to that of ketamine, and had an approximate 12-fold lower affinity than PCP. These results support the anecdotal reports of dissociative effects from 3-MeO-PCMo in humans.

Ketamine-A Narrative Review of Its Uses in Medicine

One of the most fascinating drugs in the anesthesiologist's armament is ketamine, an N-methyl-D-aspartate receptor antagonist with a myriad of uses. The drug is a dissociative anesthetic and has been used more often as an analgesic in numerous hospital units, outpatient pain clinics, and in the prehospital realm. It has been used to treat postoperative pain, chronic pain, complex regional pain syndrome, phantom limb pain, and other neuropathic conditions requiring analgesia. Research has also demonstrated its efficacy as an adjunct in psychotherapy, as a treatment for both depression and posttraumatic stress disorder, as a procedural sedative, and as a treatment for respiratory and neurologic conditions. Ketamine is not without its adverse effects, some of which can be mitigated with certain efforts. Such effects make it necessary for the clinician to use the drug only in situations where it will provide the greatest benefit with the fewest adverse effects. To the best of our knowledge, none of the reviews regarding ketamine have taken a comprehensive look at the drug's uses in all territories of medicine. This review will serve to touch on its chemical data, pharmacokinetics and pharmacodynamics, medical uses, and adverse effects while focusing specifically on the drugs usage in anesthesia and analgesia.

Analgesic effect and safety of single-dose intra-articular magnesium after arthroscopic surgery: a systematic review and meta-analysis

To examine the analgesic effect and safety of single-dose intra-articular (IA) magnesium (Mg) after arthroscopic surgery. Pubmed, Embase and Cochrane library were searched through in January 2016. Eight RCTs and eight experimental studies were included. The IA Mg exhibited a significantly lower pain score when compared with placebo (MD, -0.41, 95% CI, -0.78 to -0.05, p = 0.03). There was no significant difference between Mg and bupivacaine in terms of pain relief and the time to first analgesic request. Furthermore, statistically significant differences both in pain score (MD, -0.62, 95% CI, -0.81 to -0.42, p < 0.00001) and time to first analgesic request (MD, 6.25, 95% CI, 5.22 to 7.29, p < 0.00001) were observed between Mg plus bupivacaine and bupivacaine alone. There was no statistically significant difference among the various groups with respect to adverse reactions. Most of the included in vitro studies reported the chondrocyte protective effect of Mg supplementation. There were also two in vivo studies showing the cartilage protective effect of IA Mg. The single-dose IA Mg following arthroscopic surgery was effective in pain relief without increasing adverse reactions, and it could also enhance the analgesic effect of bupivacaine. In addition, Mg seemed to possess the cartilage or chondrocyte protective effect based on experimental studies.

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.

Effects of the noncompetitive N-methyl-d-aspartate receptor antagonists ketamine and MK-801 on pain-stimulated and pain-depressed behaviour in rats

BACKGROUND

Pain is a significant public health concern, and current pharmacological treatments have problematic side effects and limited effectiveness. N-methyl-d-aspartate (NMDA) glutamate receptor antagonists have emerged as one class of candidate treatments for pain because of the significant contribution of glutamate signalling in nociceptive processing.

METHODS

This study compared effects of the NMDA receptor antagonists ketamine and MK-801 in assays of pain-stimulated and pain-depressed behaviour in rats. The nonsteroidal anti-inflammatory drug ketoprofen was examined for comparison as a positive control. Intraperitoneal injection of dilute acid served as an acute visceral noxious stimulus to stimulate a stretching response or depress intracranial self-stimulation (ICSS) in male Sprague-Dawley rats.

RESULTS

Ketamine (1.0-10.0 mg/kg) blocked acid-stimulated stretching but failed to block acid-induced depression of ICSS, whereas MK-801 (0.01-0.1 mg/kg) blocked both acid-stimulated stretching and acid-induced depression of ICSS. These doses of ketamine and MK-801 did not alter control ICSS in the absence of the noxious stimulus; however, higher doses of ketamine (10 mg/kg) and MK-801 (0.32 mg/kg) depressed all behaviour. Ketoprofen (1.0 mg/kg) blocked both acid-induced stimulation of stretching and depression of ICSS without altering control ICSS.

CONCLUSION

These results support further consideration of NMDA receptor antagonists as analgesics; however, some NMDA receptor antagonists are more efficacious at attenuating pain-depressed behaviours.

WHAT DOES THIS STUDY ADD

NMDA receptor antagonists produce dissociable effects on pain-depressed behaviour. Provides evidence that pain-depressed behaviours should be considered and evaluated when determining the antinociceptive effects of NMDA receptor antagonists.

MAGnesium-oral supplementation to reduce PAin in patients with severe PERipheral arterial occlusive disease: the MAG-PAPER randomised clinical trial protocol

INTRODUCTION

Magnesium exerts analgaesic effects in several animal pain models, as well as in patients affected by acute postoperative pain and neuropathic chronic pain. There is no evidence that magnesium can modulate pain in patients with peripheral arterial occlusive disease (PAOD). We describe the protocol of a single-centre randomised double-blind clinical trial aimed at assessing the efficacy of oral magnesium supplementation in controlling severe pain in patients with advanced PAOD.

METHODS AND ANALYSIS

Adult patients affected by PAOD at stages III and IV of Lèriche-Fontaine classification, who are opioid-naïve, and who have been admitted to our Acute Pain Service for intractable pain, will be eligible. Patients will be randomised to the control group, treated with standard therapy (oxycodone and pregabalin) plus placebo for 2 weeks, or to the experimental group (standard therapy plus magnesium oxide). Patients will be evaluated on days 0, 2, 4, 6, 8, 12 and 14; the following information will being collected: daily oxycodone dose; average and maximum pain (Numerical Rating Scale); pain relief (Pain Relief Scale); characteristics of the pain (Neuropathic Pain Scale); impact of pain on the patient's daily activities (Brief Pain Inventory). The primary outcome will be oxycodone dosage needed to achieve satisfactory analgaesia on day 14. Secondary outcomes will be pain relief on day 2, time needed to achieve satisfactory analgaesia and time needed to achieve a pain reduction of 50%. A sample size calculation was performed for the primary outcome, which estimated a required sample size of 150 patients (75 per group).

ETHICS AND DISSEMINATION

Ethical approval of the study protocol has been obtained from Comitato Etico Provinciale di Brescia, Brescia, Italy. Trial results will be disseminated through scientific journal manuscripts and scientific conference presentations.

TRIAL REGISTRATION NUMBER

NCT02455726.

Analgesia in the Perioperative Period

Untreated or undermanaged perioperative pain has systemic effects that may negatively impact a patient's welfare and return to function. A consistent analgesic plan that assesses a patient's pain and comfort at regular intervals during the perioperative period should be incorporated into practice. Validated pain assessment tools are available for use in dogs and cats. Multimodal analgesic plans should be created for individual patients and modified according to pain assessments. These plans, based on a thorough history, physical examination, and knowledge of the expected pain, should be combinations of an opioid, a nonsteroidal anti-inflammatory drug, a local anesthetic, and nonpharmacologic analgesic techniques.

Neuronal calcium signaling in chronic pain

Acute physiological pain, the unpleasant sensory response to a noxious stimulus, is essential for animals and humans to avoid potential injury. Pathological pain that persists after the original insult or injury has subsided, however, not only results in individual suffering but also imposes a significant cost on society. Improving treatments for long-lasting pathological pain requires a comprehensive understanding of the biological mechanisms underlying pain perception and the development of pain chronicity. In this review, we aim to highlight some of the major findings related to the involvement of neuronal calcium signaling in the processes that mediate chronic pain.

Rationale and design of a multicenter randomized clinical trial with memantine and dextromethorphan in ketamine-responder patients

The N-methyl-D-aspartate receptor plays an important role in central sensitization of neuropathic pain and N-methyl-D-aspartate receptor antagonists, such as ketamine, memantine and dextromethorphan may be used for persistent pain. However, ketamine cannot be repeated too often because of its adverse events. A drug relay would be helpful in the outpatient to postpone or even cancel the next ketamine infusion. This clinical trial evaluates if memantine and/or dextromethorphan given as a relay to ketamine responders may maintain or induce a decrease of pain intensity and have a beneficial impact on cognition and quality of life. This trial is a multi-center, randomized, controlled and single-blind clinical study (NCT01602185). It includes 60 ketamine responder patients suffering from neuropathic pain. They are randomly allocated to memantine, dextromethorphan or placebo. After ketamine infusion, 60 patients received either memantine (maximal dose 20 mg/day), or dextromethorphan (maximal dose 90 mg/day), or placebo for 12 weeks. The primary endpoint is pain measured on a (0-10) Numeric Rating Scale 1 month after inclusion. Secondary outcomes include assessment of neuropathic pain, sleep, quality of life, anxiety/depression and cognitive function at 2 and 3 months. Data analysis is performed using mixed models and the tests are two-sided, with a type I error set at α=0.05. This study will explore if oral memantine and/or dextromethorphan may be a beneficial relay in ketamine responders and may diminish ketamine infusion frequency. Preservation of cognitive function and quality of life is also a central issue that will be analyzed in these vulnerable patients.

Analgesic effects of ketamine infusion therapy in korean patients with neuropathic pain: A 2-week, open-label, uncontrolled study

BACKGROUND

The overexcitation of the N-methyl-D-aspartate receptor complex appears to play a critical role in the development of neuropathic pain, and ketamine acts as an antagonist to that receptor. Some publications have reported on the prominent relief of neuropathic pain with intravenous or subcutaneous ketamine infusions or a single-dose intravenous ketamine injection despite adverse effects.

OBJECTIVES

The primary objective of this study was to determine the analgesic effect of intravenous ketamine infusion therapy for neuropathic pain refractory to conventional treatments. Secondary objectives included identifying the variables related to the analgesic effect and the pain descriptors susceptible to ketamine infusion.

METHODS

This 2-week, open-label, uncontrolled study was conducted in Korean patients with neuropathic pain recruited from the Samsung Seoul Hospital (Seoul, Republic of Korea) outpatient pain management unit. Patients were required to have a pain severity score >5 (visual analog scale [VAS], where 0 = no pain and 10 = worst pain imaginable) over a period of ≥1 month while on standard treatment. The patients were required to have shown no benefit from standard treatment and no pain relief lasting over 1 month. The ketamine infusion therapy was composed of 3 sessions performed consecutively every other day. Midazolam was administered concomitantly to reduce the occurrence of central nervous system-related adverse events (AEs) secondary to ketamine. Each session was as follows: ketamine 0.2 mg/kg and midazolam 0.1 mg/kg were administered intravenously for 5 minutes as a loading dose, followed by a continuous infusion of ketamine 0.5 mg/kg/h and midazolam 0.025 mg/kg/h for 2 hours. AEs were assessed in the following ways: close monitoring of ECG, blood pressure, oxygen saturation, and evaluating the need for treatment of AEs during infu- sion and until discharge by an attending anesthesiologist; an open question about discomfort at the end of each session; spontaneous reports about AEs during each session; and the patients' and caregivers' checklist of AEs occurring at home for 2 weeks after discharge. All the descriptors of pain expressed by the patients in Korean were recorded and translated into appropriate English terminology on the basis of the literature on Korean verbal descriptors of pain. Each of the translated pain descriptors was then classified into 1 of 18 sensory items.

RESULTS

The overall VAS score for pain decreased from a baseline mean (SD) of 7.20 (1.77) to 5.46 (2.29) (P < 0.001) 2 weeks after treatment in 103 patients (53 males and 50 females; mean age, 52.56 [17.33] years) who completed the study. Variables such as age, sex, and the duration and diagnosis of pain were not found to be associated with analgesic effect. Seven of the 18 pain descriptors were found to have a significant response to ketamine infusion treatment between baseline and 2 weeks follow-up: burning pain (P = 0.008); dull, aching pain (P < 0.001); overly sensitive to touch (P = 0.002); stabbing pain (P = 0.008); electric pain (P = 0.031); tingling pain (P < 0.001); and squeezing pain (P < 0.001). A total of 52 patients reported AEs: 33 during infusion and 44 during recovery and up to 2 weeks follow up. The most commonly reported AEs were snoring (15 [15%]) during infusion and dizziness (43 [42%]) during recovery.

CONCLUSIONS

Ketamine infusion therapy was associated with reduced severity of neuropathic pain and generally well tolerated for up to 2 weeks in these patients with neuropathic pain refractory to standard treatment. Variables such as sex, age, and the diagnosis and duration of pain had no association with the analgesic effect of this treatment. Randomized controlled trials are needed to evaluate the efficacy and tolerability of treatment with ketamine infusion.

Liquid crystal-on-organic field-effect transistor sensory devices for perceptive sensing of ultralow intensity gas flow touch

We demonstrate liquid crystal-on-organic field-effect transistor (LC-on-OFET) sensory devices that can perceptively sense ultralow level gas flows. The LC-on-OFET devices were fabricated by mounting LC molecules (4-cyano-4′-pentylbiphenyl – 5CB) on the polymer channel layer of OFET. Results showed that the presence of LC molecules on the channel layer resulted in enhanced drain currents due to a strong dipole effect of LC molecules. Upon applying low intensity nitrogen gas flows, the drain current was sensitively increased depending on the intensity and time of nitrogen flows. The present LC-on-OFET devices could detect extremely low level nitrogen flows (0.7 sccm–11 μl/s), which could not be felt by human skins, thanks to a synergy effect between collective behavior of LC molecules and charge-sensitive channel layer of OFET. The similar sensation was also achieved using the LC-on-OFET devices with a polymer film skin, suggesting viable practical applications of the present LC-on-OFET sensory devices.