Continuous subcutaneous administration of the N-methyl-D-aspartic acid (NMDA) receptor antagonist ketamine in the treatment of post-herpetic neuralgia

Comparison of Nebulized Ketamine to Intravenous Subdissociative Dose Ketamine for Treating Acute Painful Conditions in the Emergency Department: A Prospective, Randomized, Double-Blind, Double-Dummy Controlled Trial

STUDY OBJECTIVE

We aimed to assess and compare the analgesic efficacy and adverse effects of intravenous subdissociative-dose ketamine to nebulized ketamine in emergency department (ED) patients with acute painful conditions.

METHODS

We conducted a prospective, randomized, double-blind, double-dummy clinical trial in adult patients (ages 18 and older) with a numerical rating scale pain score of ≥5. We randomized subjects to receive either a single dose of 0.3 mg/kg of intravenous (IV) ketamine or 0.75 mg/kg of nebulized ketamine through a breath-actuated nebulizer. Primary outcome was the difference in pain scores on the numerical rating scale between groups at 30 minutes postmedication administration. The secondary outcomes included the need for rescue analgesia, occurrences of adverse events in each group, and the difference in pain scores at 15, 30, 60, 90, and 120 minutes. We calculated a 95% confidence interval (CI) for a mean difference at 30 minutes, with a minimum clinically important difference set at 1.3 points.

RESULTS

We enrolled 150 subjects (75 per group). Mean pain scores through numerical rating scale were 8.2 for both groups at baseline, which decreased to 3.6 and 3.8 at 30 minutes, yielding a mean difference of 0.23 (95% CI -1.32 to 0.857). We observed no clinically concerning changes in vital signs. No serious adverse events occurred in any of the groups throughout the study period.

CONCLUSION

We found no difference between the administration of IV and nebulized ketamine for the short-term treatment of moderate to severe acute pain in the ED, with both treatments providing a clinically meaningful reduction in pain scores at 30 minutes.

Application of Ketamine in Pain Management and the Underlying Mechanism

Since ketamine was approved by the FDA as an intravenous anesthetic, it has been in clinical use for more than 50 years. Apart from its anesthetic effects, ketamine is one of the few intravenous anesthetics with potent analgesic properties. As part of the effort to develop pain management, renewed interest has focused on the use of ketamine for the treatment of acute and chronic pain. Ketamine is commonly used to treat various kinds of chronic pain syndromes and is also applied to control perioperative pain and reduce the consumption of postoperative analgesics. However, its precise mechanisms of action remain mysterious for a large part. Despite extensive research in the field, the mechanism of ketamine is still unclear. Its analgesic effect appears to be largely mediated by blockade of NMDARs, but opioid, GABA, and monoaminergic system seem to partly participate in the pain transmission procedure. Its metabolites also have an analgesic effect, which may prolong pain relief. More recently, the antidepressant effect of ketamine has been considered to reduce pain-related aversion to relieve chronic pain. Overall, the analgesic mechanism of ketamine seems to be a complex combination of multiple factors. Due to its potent analgesic properties, ketamine is an analgesic with great clinical application prospects. Exploring the precise mechanism of action of ketamine will help guide clinical medication and confirm indications for ketamine analgesia. This review aims to list the application of ketamine in pain management and discuss its analgesic mechanism.

Nebulized Ketamine Used for Managing Ankle Fracture in the Prehospital Emergency Setting: A Case Report

INTRODUCTION

Acute traumatic limb injury is a common complaint of patients presenting to the emergency department (ED). Ketamine is an effective analgesic administered via intravenous (IV), intranasal (IN), intramuscular (IM), and nebulized routes in the ED. It has also been used in the prehospital setting via IV, IM, and IN routes. Recent studies have proposed the prehospital use of nebulized ketamine via breath-actuated nebulizer (BAN) as a noninvasive and effective method of analgesic delivery, as well as an alternative to opioid analgesia.

CASE REPORT

We present a case of a patient with right ankle fracture after a 12-foot fall who subsequently received 0.75 milligrams per kilogram of nebulized ketamine via BAN in the prehospital setting. The patient reported improvement of pain from 8/10 to 3/10 on the pain scale without need for additional pain medication during prehospital transport. This report supports the use of nebulized ketamine via BAN in the prehospital setting for acute traumatic limb injuries.

CONCLUSION

The use of nebulized ketamine via BAN in the prehospital setting may be an effective analgesic option for the management of patients with acute traumatic limb injuries, particularly in those with difficult IV access, where mucosal atomization devices are not accessible, or where opioid-sparing treatments are preferable.

Targeting Affective Mood Disorders With Ketamine to Prevent Chronic Postsurgical Pain

The phencyclidine-derivative ketamine [2-(2-chlorophenyl)-2-(methylamino)cyclohexan-1-one] was added to the World Health Organization's Model List of Essential Medicines in 1985 and is also on the Model List of Essential Medicines for Children due to its efficacy and safety as an intravenous anesthetic. In sub-anesthetic doses, ketamine is an effective analgesic for the treatment of acute pain (such as may occur in the perioperative setting). Additionally, ketamine may have efficacy in relieving some forms of chronic pain. In 2019, Janssen Pharmaceuticals received regulatory-approval in both the United States and Europe for use of the S-enantiomer of ketamine in adults living with treatment-resistant major depressive disorder. Pre-existing anxiety/depression and the severity of postoperative pain are risk factors for development of chronic postsurgical pain. An important question is whether short-term administration of ketamine can prevent the conversion of acute postsurgical pain to chronic postsurgical pain. Here, we have reviewed ketamine's effects on the biopsychological processes underlying pain perception and affective mood disorders, focusing on non-NMDA receptor-mediated effects, with an emphasis on results from human trials where available.

Analgesic Efficacy of Oral Aspirin/Ketamine Combination for Management of Acute Musculoskeletal Pain in the Emergency Department - A Proof of Concept Pilot Study

BACKGROUND

Musculoskeletal pain (MSK) affects one out of three adults and is the most common source of significant long-term pain, physical disability, and under-treatment in the emergency department (ED).

OBJECTIVE

We aimed to assess the analgesic efficacy of a combination of oral VTS-Aspirin® (Vitalis Analgesics, New York, NY) and ketamine in managing acute MSK pain in adult ED patients.

METHODS

This was a prospective, proof-of-concept, single-arm, pilot study evaluating the analgesic efficacy of a single dose of oral combination of VTS-Aspirin and ketamine in adult ED patients with acute moderate-to-severe MSK pain. The primary outcome included the difference in pain scores on an 11-point numeric pain rating scale at 60 min. Secondary outcomes included the need for rescue analgesia, the occurrence of adverse events at 60 min, and a change in pain scores at 120 min.

RESULTS

We enrolled 25 subjects in the study. The mean baseline pain score was 8.6 and the mean pain score at 60 min decreased to 4.8. The oral ketamine dose ranged from 24 mg to 50 mg, with a mean dose of 37.8 mg. No clinically concerning changes in vital signs were noted. No serious adverse events occurred in any of the subjects. Majority of adverse effects were transient and weak in intensity.

CONCLUSION

We demonstrated that administration of an oral combination of VTS-Aspirin and ketamine to adult ED patients with acute MSK pain resulted in clinically significant pain relief in 80% of enrolled subjects.

Three Birds, One Excipient: Development of an Improved pH, Isotonic, and Buffered Ketamine Formulation for Subcutaneous Injection

Subcutaneous (SC) ketamine has been found to be effective in pain management, though reports of injection site irritation and sterile abscesses exist with currently available ketamine HCl formulations. Such adverse SC reactions are commonly associated with low pH, high osmolality and/or high injection volumes. An optimal SC formulation of ketamine would thus have a pH and osmolality close to physiological levels, without compromising on concentration and, thus, injection volume. Such a formulation should also be buffered to maintain the pH at the acceptable level for extended time periods. As many of these physicochemical properties are interrelated, achieving these aims represented a significant challenge in formulation development. We describe the development of a novel Captisol^®-based formulation strategy to achieve an elevated pH, isosmotic and buffered formulation of ketamine (hence, three birds, one excipient) without compromising on concentration. This strategy has the potential to be readily adapted to other amine-based APIs.

A novel computational technique for the quantification of temporal summation in healthy individuals

BACKGROUND

The pathophysiology of chronic musculoskeletal pain is linked to the neurophysiologic condition known as central sensitization. Developing reliable, sensitive and clinically feasible techniques for quantifying central sensitization is a timely priority for advancing the field of chronic pain diagnosis and management.

OBJECTIVE

To compare the sensitivity of the Windup Ratio, a commonly employed Quantitative Sensory Testing (QST) technique, to a novel approach, the Sumsquare method, for detecting changes in experimentally induced central sensitization.

DESIGN

Individual, randomized, controlled experimental study.

METHODS

A total of 37 subjects assigned to experimental (N = 18) and control (N = 19) groups. Central sensitization was experimentally induced in the C5-C6 spinal segments using topical capsaicin (0.075%); controls received a non-sensitizing placebo (Lubriderm). Windup (temporal summation) was assessed using weighted pinpricks (MRC Systems, Heidelberg, Germany) applied within regions of secondary hyperalgesia surrounding the topical capsaicin. A train of 10 stimuli was applied at baseline, 10, 20 and 30 min post-topical application and participants provided numeric pain ratings after each pinprick application. Sumsquare and Windup Ratio outcomes were calculated using the pain rating data.

RESULTS

Sumsquare outcome was significantly increased at all time points (10, 20, 30 min) post-sensitization (p < 0.05); in contrast, no differences in Windup Ratio from baseline were observed at any time point post-sensitization (p > 0.05).

CONCLUSIONS

Sumsquare outcome offers greater sensitivity than Windup Ratio for detecting changes in experimentally induced central sensitization. These findings introduce a novel method for assessing changes in central sensitization in patients presenting with chronic musculoskeletal pain hypersensitivity.

Comparison of Nebulized Ketamine at Three Different Dosing Regimens for Treating Painful Conditions in the Emergency Department: A Prospective, Randomized, Double-Blind Clinical Trial

STUDY OBJECTIVE

We aimed to assess and compare the analgesic efficacies and adverse effects of ketamine administered through a breath-actuated nebulizer at 3 different dosing regimens for emergency department patients presenting with acute and chronic painful conditions.

METHODS

This was a prospective, randomized, double-blinded trial comparing 3 doses of nebulized ketamine (0.75 mg/kg, 1 mg/kg, and 1.5 mg/kg) administered through breath-actuated nebulizer in adult emergency department patients aged 18 years and older with moderate to severe acute and chronic pain. The primary outcome included the difference in pain scores on an 11-point numeric rating scale between all 3 groups at 30 minutes. Secondary outcomes included the need for rescue analgesia (additional doses of nebulized ketamine or intravenous morphine) and adverse events in each group at 30 and 60 minutes.

RESULTS

We enrolled 120 subjects (40 per group). The difference in mean pain scores at 30 minutes between the 0.75 mg/kg and 1 mg/kg groups was 0.25 (95% confidence interval [CI] 1.28 to 1.78); between the 1 mg/kg and 1.5 mg/kg groups was -0.225 (95% CI -1.76 to 1.31); and between the 0.75 mg/kg and 1.5 mg/kg groups was 0.025 (95% CI -1.51 to 1.56). No clinically concerning changes in vital signs occurred. No serious adverse events occurred in any of the groups.

CONCLUSION

We found no difference between all 3 doses of ketamine administered through breath-actuated nebulizer for short-term treatment of moderate to severe pain in the emergency department.

A randomized, noninferiority, controlled trial of two doses of intravenous subdissociative ketamine for analgesia in the emergency department

OBJECTIVE

This study aimed to determine if 0.15 mg/kg intravenous (IV) subdissociative ketamine is noninferior to 0.3 mg/kg in emergency department (ED) patients with acute pain.

METHODS

This randomized, prospective, double-blinded, noninferiority trial included patients' age 18 to 59 years presenting to the ED with acute moderate to severe pain. Subjects were randomized to IV subdissociative ketamine, 0.15 mg/kg ("low" dose) or 0.30 mg/kg ("high" dose), over 15 minutes. The primary endpoint was the 11-point numeric rating scale (NRS) pain score between groups at 30 minutes. Secondary endpoints included NRS pain scores at 15 and 60 minutes; change in NRS at 15, 30, and 60 minutes; rescue analgesia; and adverse effects. The noninferiority limit, δ₀ , was set to 1.3.

RESULTS

Forty-nine patients were included in each group. After the differences in the baseline NRS score were adjusted for, the mean NRS score at 30 minutes was 4.7 (95% confidence interval [CI] = 3.8 to 5.5) in the low-dose group and 5.0 (95% CI = 4.2 to 5.8) in the high-dose group (mean difference = 0.4, 95% CI = -0.8 to 1.5), indicating that the low-dose subdissociative ketamine was noninferior to the high dose (lower limit of 95% CI = -0.8 to ≥1.3 = -δ₀ ). Adverse effects were similar at 30 minutes. At 15 minutes, the high-dose group experienced greater change in NRS; however, more adverse effects occurred.

CONCLUSION

Our data did not detect a large difference in analgesia or adverse effect profile between 0.15 mg/kg IV ketamine and 0.30 mg/kg in the short-term treatment of acute pain in the ED.

Nebulized ketamine for managing acute pain in the pediatric emergency department: A case series

Administration of sub-dissociative doses of ketamine is used via intranasal (IN) and intravenous routes in the pediatric emergency department for managing acute pain. Due to difficulties in both obtaining intravenous access and compliance with IN medications in children, administration of ketamine via breath-actuated nebulizer can serve as a valuable modality for timely analgesia in children where dosing titration is patient controlled. We describe five pediatric patients who received ketamine via breath-actuated nebulizer at 0.75 mg/kg, 1 mg/kg, and 1.5 mg/kg, with all patients experiencing a decrease in pain score. This case series introduces ketamine inhalation as a modality for managing pain in children.

Ketamine-50 years in use: from anesthesia to rapid antidepressant effects and neurobiological mechanisms

Over the past 50 years, ketamine has solidified its position in both human and veterinary medicine as an important anesthetic with many uses. More recently, ketamine has been studied and used for several new indications, ranging from chronic pain to drug addiction and post-traumatic stress disorder. The discovery of the rapid-acting antidepressant effects of ketamine has resulted in a surge of interest towards understanding the precise mechanisms driving its effects. Indeed, ketamine may have had the largest impact for advancements in the research and treatment of psychiatric disorders in the past few decades. While intense research efforts have been aimed towards uncovering the molecular targets underlying ketamine's effects in treating depression, the underlying neurobiological mechanisms remain elusive. These efforts are made more difficult by ketamine's complex dose-dependent effects on molecular mechanisms, multiple pharmacologically active metabolites, and a mechanism of action associated with the facilitation of synaptic plasticity. This review aims to provide a brief overview of the different uses of ketamine, with an emphasis on examining ketamine's rapid antidepressant effects spanning molecular, cellular, and network levels. Another focus of the review is to offer a perspective on studies related to the different doses of ketamine used in antidepressant research. Finally, the review discusses some of the latest hypotheses concerning ketamine's action.

A review of the clinical applications of ketamine in pediatric oncology

Ketamine is a dissociative anesthetic agent with excellent analgesic properties and a favorable safety profile. The feasibility and efficacy of various routes of administration have been established, including intravenous (IV), intramuscular (IM), oral, intranasal, rectal, and transdermal routes. The advent of newer anesthetic agents has led to a decline in the use of ketamine as an anesthetic, but its utility in short-term sedation and analgesia has expanded. Its value for chronic pain management in children with cancer is being increasingly recognized but requires more evidence. The use of topical ketamine is largely in investigational stages. Medical use of ketamine is, to a great extent, free from significant long-term neurological side effects. The objective of this review is to provide a brief account of the pharmacology of ketamine and primarily focus on the clinical applications of ketamine in pediatric oncology.

Neuropathic Pain: Mechanism-Based Therapeutics

Neuropathic pain (NeP) can result from sources as varied as nerve compression, channelopathies, autoimmune disease, and incision. By identifying the neurobiological changes that underlie the pain state, it will be clinically possible to exploit mechanism-based therapeutics for maximum analgesic effect as diagnostic accuracy is optimized. Obtaining sufficient knowledge regarding the neuroadaptive alterations that occur in a particular NeP state will result in improved patient analgesia and a mechanism-based, as opposed to a disease-based, therapeutic approach to facilitate target identification. This will rely on comprehensive disease pathology insight; our knowledge is vastly improving due to continued forward and back translational preclinical and clinical research efforts. Here we discuss the clinical aspects of neuropathy and currently used drugs whose mechanisms of action are outlined alongside their clinical use. Finally, we consider sensory phenotypes, patient clusters, and predicting the efficacy of an analgesic for neuropathy.

Neurotransmitter and tryptophan metabolite concentration changes in the complete Freund's adjuvant model of orofacial pain

BACKGROUND

The neurochemical background of the evolution of headache disorders, still remains partially undiscovered. Accordingly, our aim was to further explore the neurochemical profile of Complete Freund's adjuvant (CFA)-induced orofacial pain, involving finding the shift point regarding small molecule neurotransmitter concentrations changes vs. that of the previously characterized headache-related neuropeptides. The investigated neurotransmitters consisted of glutamate, γ-aminobutyric acid, noradrenalin and serotonin. Furthermore, in light of its influence on glutamatergic neurotransmission, we measured the level of kynurenic acid (KYNA) and its precursors in the kynurenine (KYN) pathway (KP) of tryptophan metabolism.

METHODS

The effect of CFA was evaluated in male Sprague Dawley rats. Animals were injected with CFA (1 mg/ml, 50 μl/animal) into the right whisker pad. We applied high-performance liquid chromatography to determine the concentrations of the above-mentioned compounds from the trigeminal nucleus caudalis (TNC) and somatosensory cortex (ssCX) of rats. Furthermore, we measured some of these metabolites from the cerebrospinal fluid and plasma as well. Afterwards, we carried out permutation t-tests as post hoc analysis for pairwise comparison.

RESULTS

Our results demonstrated that 24 h after CFA treatment, the level of glutamate, KYNA and that of its precursor, KYN was still elevated in the TNC, all diminishing by 48 h. In the ssCX, significant concentration increases of KYNA and serotonin were found.

CONCLUSION

This is the first study assessing neurotransmitter changes in the TNC and ssCX following CFA treatment, confirming the dominant role of glutamate in early pain processing and a compensatory elevation of KYNA with anti-glutamatergic properties. Furthermore, the current findings draw attention to the limited time interval where medications can target the glutamatergic pathways.

Intravenous Ketamine Infusion for Complex Regional Pain Syndrome: Survey, Consensus, and a Reference Protocol

OBJECTIVE

To find and reach a consensus on the usage of ketamine in the treatment of complex regional pain syndrome and to determine a reference protocol for future studies.

DESIGN

Three hundred fifty-one medical professionals participated in our survey on practice procedures, with 104 respondents providing information on their usage of ketamine for treating the pain associated with complex regional pain syndrome. Respondents answered questions about inpatient treatment, outpatient treatment, children vs adults, safety, and basic demographic information. An expert group then met to reach a consensus for a reference protocol.

RESULTS

There is a difference in how inpatients are treated compared with outpatients, making it necessary to have two different reference protocols. The duration of pain relief varied from one to 10 days to one to six months, with a correlation between the duration of pain relief and total infusion hours per round.

CONCLUSIONS

The consensus reference protocols are made up of nine recommended topics. Reference protocols need to be validated by extensive research before guidelines can be created.

Administration of Nebulized Ketamine for Managing Acute Pain in the Emergency Department: A Case Series

Ketamine administration in sub-dissociative doses in the emergency department (ED) results in effective pain relief in patients with acute traumatic and non-traumatic pain, chronic pain, and opioid-tolerant pain. This case series describes five adult ED patients who received nebulized ketamine for predominantly acute traumatic pain. Three patients received nebulized ketamine at 1.5 milligrams per kilogram (mg/kg) dose, one patient at 0.75 mg/kg, and one patient at 1 mg/kg. All five patients experienced a decrease in pain from the baseline up to 120 minutes. The inhalation route of ketamine delivery via breath-actuated nebulizer may have utility for managing pain in the ED.

Ketamine applications beyond anesthesia - A literature review

Ketamine's clinical use began in the 1970s. Physicians benefited from its safety and ability to induce short-term anesthesia and analgesia. The psychodysleptic effects caused by the drug called its further clinical use into question. Despite these unpleasant effects, ketamine is still applied in veterinary medicine, field medicine, and specialist anesthesia. Recent intensive research brought into light new possible applications of this drug. It began to be used in acute, chronic and cancer pain management. Most interesting reports come from research on the antidepressive and antisuicidal properties of ketamine giving hope for the creation of an effective treatment for major depressive disorder. Other reports highlight the possible use of ketamine in treating addiction, asthma and preventing cancer growth. Besides clinical use, the drug is also applied to in animal model of schizophrenia. It seems that nowadays, with numerous possible applications, the use of ketamine has returned; to its former glory. Nevertheless, the drug must be used with caution because still the mechanisms by which it executes its functions and long-term effects of its use are not fully known. This review aims to discuss the well-known and new promising applications of ketamine.

Slow Infusion of Low-dose Ketamine Reduces Bothersome Side Effects Compared to Intravenous Push: A Double-blind, Double-dummy, Randomized Controlled Trial

OBJECTIVE

We compared the analgesic efficacy and incidence of side effects when low-dose (0.3 mg/kg) ketamine (LDK) is administered as a slow infusion (SI) over 15 minutes versus an intravenous push (IVP) over 1 minute.

METHODS

This was a prospective, randomized, double-blind, double-dummy, placebo-controlled trial of adult ED patients presenting with moderate to severe pain (numerical rating scale [NRS] score ≥ 5). Patients received 0.3 mg/kg ketamine administered either as a SI or a IVP. Our primary outcome was the proportion of patients experiencing any psychoperceptual side effect over 60 minutes. A secondary outcome was incidence of moderate or greater psychoperceptual side effects. Additional outcomes included reduction in pain NRS scores at 60 minutes and percent maximum summed pain intensity difference (%SPID).

RESULTS

Fifty-nine participants completed the study. A total of 86.2% of the IVP arm and 70.0% of the SI arm experienced any side effect (difference = 16.2%, 95% confidence interval [CI] = -5.4 to 37.8). We found a large reduction in moderate or greater psychoperceptual side effects with SI administration-75.9% reported moderate or greater side effects versus 43.4% in the SI arm (difference = 32.5%, 95% CI = 7.9 to 57.1). Additionally, the IVP arm experienced more hallucinations (n = 8, 27.6%) than the SI arm (SI n = 2, 6.7%, difference = 20.9%, 95% CI = 1.8 to 43.4). We found no significant differences in analgesic efficacy. At 60 minutes, the mean %SPID values in the IVP and SI arms were 39.9 and 33.5%, respectively, with a difference of 6.5% (95% CI = -5.8 to 18.7).

CONCLUSION

Most patients who are administered LDK experience a psychoperceptual side effect regardless of administration via SI or IVP. However, patients receiving LDK as a SI reported significantly fewer moderate or greater psychoperceptual side effects and hallucinations with equivalent analgesia.

Ketamine and Ketamine Metabolite Pharmacology: Insights into Therapeutic Mechanisms

Ketamine, a racemic mixture consisting of (S)- and (R)-ketamine, has been in clinical use since 1970. Although best characterized for its dissociative anesthetic properties, ketamine also exerts analgesic, anti-inflammatory, and antidepressant actions. We provide a comprehensive review of these therapeutic uses, emphasizing drug dose, route of administration, and the time course of these effects. Dissociative, psychotomimetic, cognitive, and peripheral side effects associated with short-term or prolonged exposure, as well as recreational ketamine use, are also discussed. We further describe ketamine's pharmacokinetics, including its rapid and extensive metabolism to norketamine, dehydronorketamine, hydroxyketamine, and hydroxynorketamine (HNK) metabolites. Whereas the anesthetic and analgesic properties of ketamine are generally attributed to direct ketamine-induced inhibition of N-methyl-D-aspartate receptors, other putative lower-affinity pharmacological targets of ketamine include, but are not limited to, γ-amynobutyric acid (GABA), dopamine, serotonin, sigma, opioid, and cholinergic receptors, as well as voltage-gated sodium and hyperpolarization-activated cyclic nucleotide-gated channels. We examine the evidence supporting the relevance of these targets of ketamine and its metabolites to the clinical effects of the drug. Ketamine metabolites may have broader clinical relevance than was previously considered, given that HNK metabolites have antidepressant efficacy in preclinical studies. Overall, pharmacological target deconvolution of ketamine and its metabolites will provide insight critical to the development of new pharmacotherapies that possess the desirable clinical effects of ketamine, but limit undesirable side effects.

Intravenous subdissociative-dose ketamine versus morphine for acute geriatric pain in the Emergency Department: A randomized controlled trial

STUDY OBJECTIVE

We compare the analgesic efficacy and safety of subdissociative intravenous-dose ketamine (SDK) versus morphine in geriatric Emergency Department (ED) patients.

METHODS

This was a prospective, randomized, double-blind trial evaluating ED patients aged 65 and older experiencing moderate to severe acute abdominal, flank, musculoskeletal, or malignant pain. Patients were randomized to receive SDK at 0.3 mg/kg or morphine at 0.1 mg/kg by short intravenous infusion over 15 min. Evaluations occurred at 15, 30, 60, 90, and 120 min. Primary outcome was reduction in pain at 30 min. Secondary outcomes included overall rates of adverse effects and incidence of rescue analgesia.

RESULTS

Thirty patients per group were enrolled in the study. The primary change in mean pain scores was not significantly different in the ketamine and morphine groups: 9.0 versus 8.4 at baseline (mean difference 0.6; 95% CI -0.30 to 1.43) and 4.2 versus 4.4 at 30 min (mean difference -0.2; 95% CI -1.93 to1.46). Patients in the SDK group reported higher rates of psychoperceptual adverse effects at 15, 30, and 60 min post drug administration. Two patients in the ketamine group and one in the morphine group experienced brief desaturation episodes. There were no statistically significant differences with respect to changes in vital signs and need for rescue medication.

CONCLUSION

SDK administered at 0.3 mg/kg over 15 min provides analgesic efficacy comparable to morphine for short-term treatment of acute pain in the geriatric ED patients but results in higher rates of psychoperceptual adverse effects. ClinicalTrials.gov Registration #: NCT02673372.

Continuous Subcutaneous Infusion of Ketorolac in Cancer Neuropathic Pain Unresponsive to Opioid and Adjuvant Drugs. A Case Report

Ketorolac is a new non-steroidal anti-inflammatory drug (NSAID) having a potent nonopioid analgesic activity. Administered by continuous subcutaneous infusion (CSI), its analgesic efficacy has been documented in the treatment of somatic and visceral cancer pain whilst it has been shown to be ineffective in the treatment of neuropathic pain. Here is a description of a cancer patient with neuropathic pain unresponsive to anticonvulsant or antidepressant drugs administered in association or not with oral opioids but who was successfully treated with ketorolac alone via CSI. Furthermore, the analgesia lasted over 75 days of treatment without any significant renal and gastric side effects.

A prospective randomized, double-dummy trial comparing IV push low dose ketamine to short infusion of low dose ketamine for treatment of pain in the ED

STUDY OBJECTIVE

Compare adverse effects and analgesic efficacy of low-dose ketamine for acute pain in the ED administered either by single intravenous push (IVP) or short infusion (SI).

METHODS

Patients 18-65, presenting to ED with acute abdominal, flank, or musculoskeletal pain with initial pain score≥5, were randomized to ketamine 0.3mg/kg by either IVP or SI with placebo double-dummy. Adverse effects were evaluated by Side Effects Rating Scale for Dissociative Anesthetics (SERSDA) and Richmond Agitation-Sedation Scale (RASS) at 5, 15, 30, 60, 90, and 120min post-administration; analgesic efficacy was evaluated by Numerical Rating Scale (NRS).

RESULTS

48 patients enrolled in the study. IVP group had higher overall rates of feeling of unreality on SERSDA scale: 92% versus 54% (difference 37.5%; p=0.008; 95% CI 9.3-59.5%). At 5min median severity of feeling of unreality was 3.0 for IVP versus 0.0 for SI (p=0.001). IVP also showed greater rates of sedation on RASS scale at 5min: median RASS -2.0 versus 0.0 (p=0.01). Decrease in mean pain scores from baseline to 15min was similar across groups: 5.2±3.53 (95% CI 3.7-6.7) for IVP; 5.75±3.48 (95% CI 4.3-7.2) for SI. There were no statistically significant differences with respect to changes in vital signs and need for rescue medication.

CONCLUSION

Low-dose ketamine given as a short infusion is associated with significantly lower rates of feeling of unreality and sedation with no difference in analgesic efficacy in comparison to intravenous push.

The role of ketamine in the treatment of chronic cancer pain

Background and aim

Ketamine is a drug used for the induction and maintenance of general anesthesia, for the treatment of postoperative and posttraumatic acute pain, and more recently, for the reduction of postoperative opioid requirements. The main mechanism of action of ketamine is the antagonization of N-methyl-D-aspartate (NMDA) receptors that are associated with central sensitization. In the pathogenesis of chronic pain and particularly in neuropathic pain, an important role is played by the activation of NMDA receptors. Although ketamine is indicated and used for the treatment of chronic cancer pain as an adjuvant to opioids, there are few clinical studies that clearly demonstrate the effectiveness of ketamine in this type of pain.

The aim of this study is to analyze evidence-based clinical data on the effectiveness and safety of ketamine administration in the treatment of chronic neoplastic pain, and to summarize the evidence-based recommendations for the use of ketamine in the treatment of chronic cancer pain.

Method

We reviewed the literature from the electronic databases of MEDLINE, COCHRANE, PUBMED, MEDSCAPE (1998–2014), as well as chapters of specialized books (palliative care, pain management, anesthesia).

Results

A number of studies support the effectiveness of ketamine in the treatment of chronic cancer pain, one study does not evidence clear clinical benefits for the use of ketamine, and some studies included too few patients to be conclusive.

Conclusions

Ketamine represents an option for neoplasic pain that no longer responds to conventional opioid treatment, but this drug should be used with caution, and the development of potential side effects should be carefully monitored.

Analysis of genotoxic activity of ketamine and rocuronium bromide using the somatic mutation and recombination test in Drosophila melanogaster

The present study evaluated the mutagenic and recombinogenic effects of two commonly used anesthetic agents, ketamine and rocuronium bromide, in medicine using the wing somatic mutation and recombination test (SMART) in Drosophila. The standard (ST) cross and the high-bioactivation (HB) cross with high sensitivity to procarcinogens and promutagens were used. The SMART test is based on the loss of heterozygosity, which occurs via various mechanisms, such as chromosome loss and deletion, half-translocation, mitotic recombination, mutation, and non-disjunction. Genetic alterations occurring in the somatic cells of the wing's imaginal discs result in mutant clones in the wing blade. Three-day-old trans-heterozygous larvae with two recessive markers, multiple wing hairs (mwh) and flare (flr(3)), were treated with ketamine and rocuronium bromide. Analysis of the ST cross indicated that ketamine exhibited genotoxicity activity and that this activity was particularly dependent on homologous mitotic recombination at concentrations of 250 μg/ml and above. Rocuronium bromide did not exert mutagenic and/or recombinogenic effects. In the HB cross, ketamine at a concentration of 1000 μg/ml and rocuronium bromide at all concentrations, with the exception of 250 μg/ml (inconclusive), exerted genotoxic effects, which could also be associated with the increase in mitotic recombination.

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.

The glutamatergic system as a target for neuropathic pain relief

Glutamate is the major excitatory neurotransmitter in the mammalian CNS. The understanding of glutamatergic transmission in the nervous system has been greatly expanded with the discovery and investigation of the family of ionotropic and metabotropic glutamate receptors (mGluRs). Metabotropic glutamate receptors are localized at nerve terminals, postsynaptic sites and glial cells and thus, they can influence and modulate the action of glutamate at different levels in the synapse. Moreover, there is substantial evidence of glial participation in glutamate nociceptive processes and neuropathic pain. Metabotropic glutamate receptors have been shown to play a role in neuropathic pain, which is one of the most troublesome illnesses because the therapy is still not satisfactory. Recently, the development of selective mGluR ligands has provided important tools for further investigation of the role of mGluRs in the modulation of chronic pain processing. This paper presents a review of the literature of glutamate receptors in neuropathic pain and the role of glia in these effects. Specifically, pharmacological interventions aimed at inhibiting group I mGluRs and/or potentiating group II and III mGluR-mediated signalling is discussed. Moreover, we introduce data about the role of glutamate transporters. They are responsible for the level of glutamate in the synaptic cleft and thus regulate the effects of all three groups of mGluRs and, in consequence, the activity of this system in nociceptive transmission. Additionally, the question of how the modulation of the glutamatergic system influences the effectiveness of analgesic drugs used in neuropathic pain therapy is addressed.

Can Gradual Dose Titration of Ketamine for Management of Neuropathic Pain Prevent Psychotomimetic Effects in Patients With Advanced Cancer?

Background:

Ketamine is often used to manage neuropathic pain in patients with cancer. However, it occasionally causes psychotomimetic effects such as vivid dreams, nightmares, illusions, hallucinations, and altered body image. Objective: To examine whether gradual dose titration of ketamine for management of neuropathic pain prevents psychotomimetic effects in patients with advanced cancer.

Methods:

This was a retrospective chart review. We administered ketamine when neuropathic pain in patients with advanced cancer became refractory to opioids and oral adjuvant analgesics. The starting dose of ketamine was 10 mg/d by continuous intravenous infusion. The dose was gradually increased by 10 mg/d every 4 to 6 hours to 50 mg/d or until the pain was relieved. It was subsequently increased by 25 mg/d every 12 to 24 hours until the pain was relieved.

Results:

For this study, we enrolled 46 patients with advanced cancer. The mean age was 52.2 ± 16.9 years. The mean dose at onset of action and maximum dose of ketamine were 56 ± 58 and 272 ± 214 mg/d, respectively. The mean pain intensity (numerical rating scale) decreased significantly from 7.3 ± 2.0 to 3.5 ± 2.2 after the administration of ketamine ( P < .01). The effectiveness was 69.5%. No psychotomimetic effect of less than 300 mg/d was observed during the introduction phase even though psychotropic drugs were not prescribed. Mild sedation was observed in 3 patients (7%) as the only adverse effect during the introduction phase.

Conclusion:

Gradual dose titration of ketamine for management of neuropathic pain can prevent psychotomimetic effects in patients with advanced cancer.

Human experimental pain models for assessing the therapeutic efficacy of analgesic drugs

Pain models in animals have shown low predictivity for analgesic efficacy in humans, and clinical studies are often very confounded, blurring the evaluation. Human experimental pain models may therefore help to evaluate mechanisms and effect of analgesics and bridge findings from basic studies to the clinic. The present review outlines the concept and limitations of human experimental pain models and addresses analgesic efficacy in healthy volunteers and patients. Experimental models to evoke pain and hyperalgesia are available for most tissues. In healthy volunteers, the effect of acetaminophen is difficult to detect unless neurophysiological methods are used, whereas the effect of nonsteroidal anti-inflammatory drugs could be detected in most models. Anticonvulsants and antidepressants are sensitive in several models, particularly in models inducing hyperalgesia. For opioids, tonic pain with high intensity is attenuated more than short-lasting pain and nonpainful sensations. Fewer studies were performed in patients. In general, the sensitivity to analgesics is better in patients than in healthy volunteers, but the lower number of studies may bias the results. Experimental models have variable reliability, and validity shall be interpreted with caution. Models including deep, tonic pain and hyperalgesia are better to predict the effects of analgesics. Assessment with neurophysiologic methods and imaging is valuable as a supplement to psychophysical methods and can increase sensitivity. The models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. Knowledge obtained from this review can help design experimental pain studies for new compounds entering phase I and II clinical trials.

Memantine attenuates responses of spinothalamic tract cells to cutaneous stimulation in neuropathic monkeys

Several lines of evidence indicate that N-methyl-D-aspartate (NMDA) receptors play an important role in nociception in general and in pathological pain in particular. It has been previously demonstrated in behavioral studies that NMDA receptor antagonists attenuate pathological pain in humans and nociceptive behaviors in animals. In the present study, we investigated the effect of the NMDA receptor antagonist memantine (MEM) on the responses of spinothalamic tract (STT) cells in normal and neuropathic monkeys. Memantine was delivered into the spinal cord through a microdialysis fiber acutely implanted into the dorsal horn. Responses of STT cells to peripheral stimulation within their receptive fields were recorded before and after MEM infusion. In normal animals (n = 7), 10 mm MEM did not affect STT cell (n = 7) baseline activity or responses to mechanical stimuli (brush, press or pinch). In neuropathic animals (n = 6), 1.0, 3.0, 10.0 and 100 mm MEM did not affect baseline activity of STT cells (n = 7); however, in a dose-dependent fashion, it significantly reduced responses of these cells to all cutaneous stimuli. The data suggest that MEM can have a direct effect on STT cells, blocking NMDA receptors known to be present on this cell population and, furthermore, may be a therapeutic agent for chronic pain.

Potentiation of μ-opioid receptor-mediated signaling by ketamine

Ketamine, a clinically relevant drug, has been shown to enhance opioid-induced analgesia and prevent hyperalgesia. However, the molecular mechanisms involved are not clearly understood. As previous studies found that activation of opioid receptors leads to the phosphorylation of mitogen-activated protein kinases, we investigated whether ketamine could modulate μ-opioid receptor (μOR)-mediated ERK1/2 phosphorylation. We find that acute treatment with ketamine enhances (∼2- to 3-fold) the levels of opioid-induced ERK1/2 phosphorylation in recombinant as well as cells endogenously expressing μOR. Interestingly, we find that in the absence of ketamine ERK1/2 signaling is desensitized 10 min after opioid exposure whereas in its presence significant levels (∼3-fold over basal) are detected. In addition, ketamine increases the rate of resensitization of opioid-mediated ERK1/2 signaling (15 min in its presence vs. 30 min in its absence). These results suggest that ketamine increases the effectiveness of opiate-induced signaling by affecting multiple mechanisms. In addition, these effects are observed in heterologous cells expressing μOR suggesting a non-NMDA receptor-mediated action of ketamine. Together this could, in part, account for the observed effects of ketamine on the enhancement of the analgesic effects of opiates as well as in the duration of opiate-induced analgesia.

Dissociative conscious sedation, an alternative to general anesthesia for laparoscopic peritoneal dialysis catheter implantation: a randomized trial comparing intravenous and subcutaneous ketamine

Laparoscopy is an effective method of implantation for peritoneal dialysis (PD) catheters. Use of the laparoscopic technique is increasing because of its potential advantages over other techniques. In most patients, selection for PD is based on negative criteria, and because of the need for general anesthesia, the laparoscopic technique can be life-threatening in these patients. On the other hand, local anesthesia is insufficient for laparoscopic catheter implantation. To avoid the need for general anesthesia and to achieve patient safety and satisfaction, we designed a type of conscious sedation (dissociative conscious sedation) and compared the efficacy of subcutaneous (SC) and intravenous (IV) ketamine added to narcotics in patients scheduled for laparoscopic implantation of a PD catheter.

METHODS

Our prospective randomized double-blind study enrolled 60 adult patients with chronic renal failure who were scheduled for laparoscopic implantation of a PD catheter. Patients were randomly assigned to one of two groups: one receiving IV ketamine, and the other receiving SC ketamine. In both groups, patients were premedicated with IV midazolam 0.015 mg/kg, fentanyl 1-2 μg/kg, and lidocaine 1.5 mg/kg. Patients then received 0.6 mg/kg ketamine either intravenously (IV group) or by subcutaneous injection at the anterior aspect of the forearm (SC group). If systolic blood pressure (BP) increased more than 20% from baseline or exceeded 170 mmHg, IV nitroglycerine (TNG) 50 μg was administered incrementally (repeated 50-μg doses). After a desirable level of conscious sedation was achieved, local anesthesia and nitrous oxide pneumoperitoneum were applied, and the PD catheter was implanted under laparoscopic guidance. Heart rate and BP were measured throughout the procedure. Adverse effects and recovery events were recorded.

RESULTS

All patients tolerated the procedure well. Administration of TNG was significantly more frequent in the IV ketamine group. Pain intensity during the surgery was similar in both groups. Both groups were comparable with regard to heart rate, but patients in the SC ketamine group had a significantly lower systolic BP at the 2nd measurement and a lower rate-pressure product at the 2nd, 4th, and 5th measurements. All patients in the SC ketamine group were cooperative during surgery and experienced uneventful recoveries; mild hallucinations were observed in 5 patients in the IV ketamine group. In the IV ketamine group, 3 patients lost the ability to cooperate during surgery. All catheters were successfully placed.

CONCLUSIONS

Dissociative conscious sedation is an acceptable alternative to general anesthesia in laparoscopic implantation of the PD catheter. Ketamine by the SC route is as effective as, but safer than, IV ketamine.

Fibromyalgia and the complex regional pain syndrome: similarities in pathophysiology and treatment

Although the pain of fibromyalgia usually is not preceded by an injury to the involved tissue, whereas that of the complex regional pain syndrome usually starts at a site of prior trauma or surgery, both disorders may share a common mechanism-pathologic sensitization of brain mechanisms that integrate nociceptive signals-and both apparently respond to treatment with ketamine, an anesthetic-analgesic agent whose actions include blockade of N-methyl-D-aspartate receptors. Ketamine's widespread illegal use as a recreational agent probably precludes developing it as a general treatment of centrally mediated pain disorders; however, its efficacy suggests that related, to-be-discovered agents could be useful.

Use of oral ketamine in chronic pain management: a review

The analgesic effect of ketamine is primarily based on the antagonism of the N-methyl-d-aspartate (NMDA) receptor. Activation of NMDA receptors may play a crucial role in the pathogenesis of chronic pain. Little formal research has been performed on the efficacy and safety of ketamine in chronic pain, especially concerning long-term oral administration. This review provides an overview of the available clinical data on the use of oral ketamine in chronic pain management. A literature search was performed in MEDLINE, EMBASE and the Cochrane Library, resulting in 22 relevant articles. Because most retrieved articles were of a descriptive nature (e.g. case reports and case series) a quantitative analysis was not possible. There was no consistent dose-response relation. A recommended starting dosage in ketamine-naive patients is 0.5 mg/kg racemic ketamine or 0.25 mg/kg S-ketamine as a single oral dose. The dosage is increased by the same amount if required. For a continuous analgesic effect it is usually given 3-4 times daily. The injection fluid can be taken orally. When parenteral ketamine is switched to oral administration the daily dosage can be kept equal and, depending on clinical effect and/or adverse effects, is slowly increased. The pharmacologically active metabolite norketamine is believed to contribute to the analgesic effect of oral ketamine. Lack of evidence regarding efficacy, and the poor safety profile, do not support routine use of oral ketamine in chronic pain management. Oral ketamine may have a limited place as add-on therapy in complex chronic pain patients if other therapeutic options have failed.

Effects of low-dose intranasal (S)-ketamine in patients with neuropathic pain

BACKGROUND

NMDA receptors are involved in the development and maintenance of neuropathic pain. We evaluated the efficacy and safety of intranasal (S)-ketamine, one of the most potent clinically available NMDA receptor antagonists.

METHODS

Sixteen patients with neuropathic pain of various origins were randomized into two treatment groups: (S)-ketamine 0.2mg/kg (group 1); (S)-ketamine 0.4mg/kg (group 2). Plasma concentrations of (S)-ketamine and (S)-norketamine were measured over 6h by High Performance Liquid Chromatography combined with mass spectrometry. Quantitative sensory testing (QST) was conducted before, during and after treatment. Side effects and amount of pain reduction were recorded.

RESULTS

Intranasal (S)-ketamine administration lead to peak plasma concentrations of 27.7+/-5.9ng/ml at 10+/-6.3min (group 1) and 34.3+/-22.2ng/ml at 13.8+/-4.8min after application (group 2). Maximal plasma concentrations of (S)-norketamine were 18.3+/-14.9ng/ml at 81+/-59min (group 1) and 34.3+/-5.5ng/ml at 75+/-40min (group 2). Pain scores decreased significantly in both groups with minimal pain at 60min after drug administration (70+/-10% and 61+/-13% of initial pain in groups 1 and 2). The time course of pain decrease was significantly correlated with plasma concentrations of (S)-ketamine and (S)-norketamine (partial correlations: (S)-norketamine: -0.90 and -0.86; (S)-ketamine: -0.72 and -0.71 for group 1 and group 2, respectively). Higher dosing elicited significantly more side effects. Intranasal (S)-ketamine had no significant impact on thermal or mechanical detection and pain thresholds in normal or symptomatic skin areas.

CONCLUSIONS

Intranasal administration of low dose (S)-ketamine rapidly induces adequate plasma concentrations of (S)-ketamine and subsequently of its metabolite (S)-norketamine. The time course of analgesia correlated with plasma concentrations.

Antinociceptive effects of chronic administration of uncompetitive NMDA receptor antagonists in a rat model of diabetic neuropathic pain

Diabetic neuropathic pain remains an unmet clinical problem and is poorly relieved by conventional analgesics. N-methyl-D-aspartate (NMDA) receptors play an important role in central sensitization in neuropathic pain. Although NMDA antagonists are highly effective in reducing neuropathic pain, these agents cause severe side effects at therapeutic doses, which limit their clinical uses. Neramexane and memantine are uncompetitive NMDA antagonists with minimal side effects at therapeutic doses. Here we determined the antinociceptive effect of chronic administration of neramexane and compared its effect with that of memantine and gabapentin in a rat model of diabetic neuropathic pain. Mechanical hyperalgesia was measured with a noxious pressure stimulus, and tactile allodynia was assessed with von Frey filaments in diabetic rats induced by streptozotocin. Compared with vehicle-treated rats, treatment with neramexane (12.3, 24.6, and 49.2 mg/kg/day) for 2 weeks via an osmotic minipump produced dose-dependent and sustained effects on mechanical hyperalgesia and allodynia. Administration of memantine (20 mg/kg/day) or gabapentin (50 mg/kg/day) for 2 weeks also produced significant and persistent antinociceptive effects on mechanical hyperalgesia and allodynia. The magnitude of the antinociceptive effect produced by the intermediate and high doses of neramexane was comparable to that of gabapentin and memantine. The plasma level achieved by neramexane at 12.3, 24.6, and 49.2 mg/kg/day was 0.26 +/- 0.04, 0.50 +/- 0.05, and 1.21 +/- 0.16 microM, respectively. These data suggest that neramexane at therapeutically relevant doses attenuates diabetic neuropathic pain. Our study provides valuable information about the therapeutic potential of chronic administration of neramexane and memantine for painful diabetic neuropathy.

Synergy between a NR2B receptor antagonist DHQ and 3-methyl-gabapentin in mice with neuropathic pain

The synergistic effect of a selective NR2B NMDA receptor antagonist, (-)-(R)-6-{2-[4-(3-Fluorophenyl)-4-hydroxy-1-piperidinyl]-1-hydroxyethyl-3,4-dihydro-2(1H)-quinolinone (DHQ), and a alpha 2 delta ligand, 3-methyl-gabapentin (3M-GBP), was investigated in the mouse partial sciatic nerve model. The interaction was observed after administration of DHQ and 3M-GBP combination at fixed dose ratios of 1:10 and 1:30 and the dose-response curves shifted approximately 13- and 17-fold leftward, respectively, from the theoretical additive values. However, a fixed dose ratio of 1:50 resulted only in an additive effect. These results indicate the synergistic interaction between DHQ and 3M-GBP in this animal model of neuropathic pain.