Ketamine for the treatment of chronic non-cancer pain

Ketamine and the neurobiology of depression: Toward next-generation rapid-acting antidepressant treatments

Ketamine has emerged as a transformative and mechanistically novel pharmacotherapy for depression. Its rapid onset of action, efficacy for treatment-resistant symptoms, and protection against relapse distinguish it from prior antidepressants. Its discovery emerged from a reconceptualization of the neurobiology of depression and, in turn, insights from the elaboration of its mechanisms of action inform studies of the pathophysiology of depression and related disorders. It has been 25 y since we first presented our ketamine findings in depression. Thus, it is timely for this review to consider what we have learned from studies of ketamine and to suggest future directions for the optimization of rapid-acting antidepressant treatment.

Maintenance IV Ketamine Therapy in the Fibromyalgia Patient: A Case Report

Introduction

Fibromyalgia is a complex disorder characterized by distributed and persistent pain often associated with fatigue and depression. The underlying causal agents of this dysfunction are not clear. Ketamine has been used to treat chronic pain in a variety of pain syndromes, including fibromyalgia, but the dosing protocols used are neither standardized nor consistent across cases. The current case presents an opportunity to contribute to a progression towards a consensus on ketamine dosing for fibromyalgia.

Case Presentation

A 60-year-old female presented with indications of fibromyalgia and was administered a 9-session IV ketamine treatment for pain. The initial dosing was 50 mg, with a concentration of 1.0 mg/ml at an infusion rate of 0.8 mg/kg/hr. This was increased to 200 mg and eventually to 240 mg, maintaining a ketamine concentration 4.0-4.8 mg/ml at an infusion rate of 1.5 mg/kg/hr.

Management and Outcomes

Following the first 9-session therapy, the patient reported >50% pain relief from pre-infusion levels and was placed on a maintenance regimen in perpetuity. This regimen involves two monthly IV ketamine infusions, one day apart for two hours at a maintenance rate of 4.8 mg/kg/hr.

Conclusion

Ketamine by IV is an effective option for pain management in patients with fibromyalgia. Compared to previous case studies, it is recommended that increased total dose, frequent administration, and longer duration of infusions all may be necessary for ketamine to maximize its beneficial effects.

Therapeutic effects of 7- to 14-day subanesthetic ketamine infusions for chronic pain on standardized psychiatric measures

Background: We have previously shown that subanesthetic ketamine infusions effectively reduce refractory pain. However, the effects of ketamine infusions on comorbid conditions of depression and anxiety have not been explored in this patient population. Methods: We investigated the effects of ketamine on mood and anxiety in patients with refractory chronic pain treated with 7-14 days of subanesthetic continuous intravenous ketamine infusions, using well-validated clinical scales. Results: There was a significant 52% reduction in pain severity and 33% reduction in pain interference scores following ketamine treatment. Ketamine treatment also reduced scores on the depression module of the Patient Health Questionnaire (PHQ-9) by 28% and scores on the Generalised Anxiety and Depression Assessment (GAD-7) by 36%. Conclusion: Multiday subanesthetic ketamine infusions effectively reduce pain, anxiety and depression in patients with complex chronic pain.

Ketamine for Complex Regional Pain Syndrome: A Narrative Review Highlighting Dosing Practices and Treatment Response

This is a narrative review of intravenous ketamine infusions for the treatment of complex regional pain syndrome (CRPS). It briefly covers the definition of CRPS, its epidemiology, and other treatments before introducing ketamine as the article's focus. A summary of ketamine's evidence base and its mechanisms of action is provided. The authors then review ketamine dosages reported in peer-reviewed literature for the treatment of CRPS, and their associated duration of pain relief. The observed response rates to ketamine and predictors of treatment response are also discussed.

Ketamine-assisted psychotherapy treatment of chronic pain and comorbid depression: a pilot study of two approaches

Chronic pain and depression diagnoses are skyrocketing. There is an urgent need for more effective treatments. Ketamine was recently established to alleviate pain and depression, but many gaps remain in the scientific literature. This paper reports the findings of an observational preliminary study that explored the efficacy of ketamine-assisted psychotherapy (KAPT) for chronic pain/major depressive disorder (MDD) comorbidity. Researchers evaluated two KAPT approaches to determine optimal route of administration/dose. Ten individuals diagnosed with a chronic pain disorder and MDD receiving KAPT were recruited: five individuals pursuing the psychedelic approach (high doses administered intramuscularly 24 h before therapy) and five individuals pursuing the psycholytic approach (low doses administered sublingually via oral lozenges during therapy). To evaluate differences between altered states of consciousness each approach induces, participants completed the Mystical Experience Questionnaire (MEQ30) after their first (T-1), third (T-2) and sixth/final (T-3) treatment sessions. Primary outcomes were change in Beck Depression Inventory (BDI) scores and Brief Pain Inventory (BPI) Short Form scores from baseline (T0) to (T-1)-(T-3). Secondary outcomes were changes in Generalized Anxiety Disorder (GAD-7) Scale scores and Post-Traumatic Stress Disorder Checklist (PCL-5) scores at each timepoint. Statistically significant differences between each approach were not observed, but the small sample's limited statistical power makes changes seen worth noting. All participants' symptoms declined throughout treatment. Psychedelic treatment participants saw a larger, more consistent decrease. Researchers conclude that KAPT may be effective for treating chronic pain/MDD comorbidity, anxiety and Post-Traumatic Stress Disorder (PTSD). Findings imply that the psychedelic approach may be more effective. This pilot study serves as a basis for more extensive research that will inform how clinicians administer treatment to optimize outcomes.

Narrative Review: Low-Dose Ketamine for Pain Management

Pain is the leading cause of medical consultations and occurs in 50-70% of emergency department visits. To date, several drugs have been used to manage pain. The clinical use of ketamine began in the 1960s and it immediately emerged as a manageable and safe drug for sedation and anesthesia. The analgesic properties of this drug were first reported shortly after its use; however, its psychomimetic effects have limited its use in emergency departments. Owing to the misuse and abuse of opioids in some countries worldwide, ketamine has become a versatile tool for sedation and analgesia. In this narrative review, ketamine's role as an analgesic is discussed, with both known and new applications in various contexts (acute, chronic, and neuropathic pain), along with its strengths and weaknesses, especially in terms of psychomimetic, cardiovascular, and hepatic effects. Moreover, new scientific evidence has been reviewed on the use of additional drugs with ketamine, such as magnesium infusion for improving analgesia and clonidine for treating psychomimetic symptoms. Finally, this narrative review was refined by the experience of the Pain Group of the Italian Society of Emergency Medicine (SIMEU) in treating acute and chronic pain with acute manifestations in Italian Emergency Departments.

Intermittent versus continuous esketamine infusions for long-term pain modulation in complex regional pain syndrome: protocol of a randomized controlled non-inferiority study (KetCRPS-2)

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic pain condition of an extremity. While achieving pain relief in CRPS is challenging, esketamine infusions can accomplish pain relief for several weeks post-infusion in a subgroup of CRPS patients. Unfortunately, CRPS esketamine protocols are very heterogeneous in advice on dosage, administration and treatment setting. Currently, no trials are available that study differences between intermittent and continuous esketamine infusions for CRPS. With the current situation of bed shortages, it is difficult to admit patients for several consecutive days for inpatient esketamine treatments. In this study, we investigate whether 6 intermittent outpatient esketamine treatments are not inferior to a continuous 6-day inpatient esketamine treatment in establishing pain relief. In addition, several secondary study parameters will be assessed in order to investigate mechanisms responsible for pain relief by esketamine infusions. Furthermore, the cost-effectiveness will be analyzed.

METHODS

In this RCT, the primary objective is to demonstrate that an intermittent esketamine dosing regimen is non-inferior to a continuous esketamine dosing regimen at 3 months follow-up. We will include 60 adult CRPS patients. The inpatient treatment group receives a continuous intravenous esketamine infusion for 6 consecutive days. The outpatient treatment group receives a 6-hour intravenous esketamine infusion every 2 weeks for 3 months. Esketamine dose will be individually tailored and is started at 0.05 mg/kg/h and can be increased to a maximum of 0.2 mg/kg/h. Each patient will be followed for 6 months. The primary study parameter is perceived pain intensity, measured by an 11-point Numerical Rating Scale. Secondary study parameters are conditioned pain modulation, quantitative sensory testing, adverse events, thermography, blood inflammatory parameter, questionnaires about functionality, quality of life and mood and costs per patient.

DISCUSSION

If our study reveals non-inferiority between intermittent and continuous esketamine infusions, these findings can be beneficial to increase the availability and flexibility of esketamine infusions through outpatient treatments. Furthermore, the costs of outpatient esketamine infusions could be lower than inpatient esketamine infusions. In addition, secondary parameters may predict response to esketamine treatment.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT05212571 , date of registration 01-28-2022.

PROTOCOL VERSION

Version 3, February 2022.

Low-dose ketamine infusions reduce opioid use in pediatric and young adult oncology patients

BACKGROUND

Ketamine is an NMDA-receptor antagonist with analgesic and opioid-sparing properties. Although well studied in adults, more robust evidence supporting ketamine's use for pediatric pain management is needed. This retrospective study evaluates ketamine's opioid-sparing effectiveness in pediatric and young adult oncology and hematology patients.

PROCEDURE

Continuous ketamine infusions administered for pain management between 2010-2020 were reviewed. Data including demographic characteristics, oncology/hematology and pain diagnoses, concurrent pain medications, and ketamine infusions' dose and duration were collected. Opioid consumption data based on delivery via patient-controlled analgesia were collected 1 day before (D1), all days during (cumulatively named D2), and 1 day after (D3) ketamine infusions and calculated as morphine-equivalent doses (mg/kg/day). Data were reported for the entire study group as well as for distinct oncology and end-of-life categories, and short-term acute pain circumstances which included vaso-occlusive crises in hematology patients. Side effects were reviewed.

RESULTS

Significantly lower daily opioid consumption was noted in the oncology group, while decreases were not significant in the end-of-life group and in the overall study population. The acute pain group did not show an opioid reduction associated with the ketamine infusions. A largely tolerable side-effect profile was observed, with no differences among each group's incidence.

CONCLUSIONS

Ketamine infusions were associated with significantly reduced opioid consumption for oncology patients. The opioid-sparing effects of ketamine may vary according to clinical diagnoses and circumstances of use. Overall, low-dose ketamine infusions present an acceptable safety profile in pediatric and young adult patients; nevertheless, individual risks and benefits should be considered.

Novel uses of ketamine in the emergency department

INTRODUCTION

: Ketamine is gaining renewed interest among healthcare providers due to its novel clinical applications in the emergency department (ED) setting.

AREAS COVERED

: This article provides a comprehensive discussion of ketamine's pharmacological properties, including safety profile and adverse effects, in addition to an overview of current evidence for ketamine (racemic formulation) in the management of ED patients with acute agitation, pain, and depression/suicide ideation.

EXPERT OPINION

: Ketamine is an effective adjunct to opioids, providing greater pain relief than morphine alone. As an analgesic agent, administration of ketamine (0.1-0.3 mg/kg IV) alone can provide analgesia similar to that of morphine in patients with acute visceral and musculoskeletal pain. Moreover, ketamine provides equal analgesic efficacy to morphine in a variety of chronic painful conditions including pain associated with cancer, vaso-occlusive pain crisis associated with sickle cell disease, and in patients with high opioid tolerance and/or opioid dependency. Available literature shows that ketamine (1-2mg/kg IV or 4-5 mg/kg IM) is a safe, rapid (<5 minutes) and effective tranquilization agent for ED patients with acute agitation. Finally, there is growing evidence that suggests ketamine may have a potential utility in the management of patients with self-harm ideation or acute depressive episodes. Intravenous infusion of ketamine (0.5 mg/kg over 40 mins) has been shown to produce an antidepressant effect and decrease in suicidal ideation within 4 hours with effects lasting up to one week.

Ketamine Assisted Psychotherapy: A Systematic Narrative Review of the Literature

Currently, ketamine is used in treating multiple pain, mental health, and substance abuse disorders due to rapid-acting analgesic and antidepressant effects. Its limited short-term durability has motivated research into the potential synergistic actions between ketamine and psychotherapy to sustain benefits. This systematic review on ketamine-assisted psychotherapy (KAP) summarizes existing evidence regarding present-day practices. Through rigorous review, seventeen articles that included 603 participants were identified. From available KAP publications, it is apparent that combined treatments can, in specific circumstances, initiate and prolong clinically significant reductions in pain, anxiety, and depressive symptoms, while encouraging rapport and treatment engagement, and promoting abstinence in patients addicted to other substances. Despite much variance in how KAP is applied (route of ketamine administration, ketamine dosage/frequency, psychotherapy modality, overall treatment length), these findings suggest psychotherapy, provided before, during, and following ketamine sessions, can maximize and prolong benefits. Additional large-scale randomized control trials are warranted to understand better the mutually influential relationships between psychotherapy and ketamine in optimizing responsiveness and sustaining long-term benefits in patients with chronic pain. Such investigations will assist in developing standardized practices and maintenance programs.

Ketamine therapy for chronic pain in The Netherlands: a nationwide survey

OBJECTIVES

Ketamine is used to treat chronic refractory pain. However, there are no scientific guidelines for ketamine use in the Netherlands. The aim of this survey was to provide an overview of the use of ketamine for chronic pain in the Netherlands.

METHODS

All pain clinics in the Netherlands were contacted. A digital survey, available from June 2019 to January 2020, was sent to 68 pain clinics. The survey was completed by one pain physician as a representative of the entire pain department. The survey included questions about ketamine treatment indications, administration, dose, duration, treatment repetition and the inpatient or outpatient setting.

RESULTS

The survey was completed by 51 pain clinics (75.0%). Thirty-one clinics used ketamine for chronic pain treatment. The most common indication was Complex Regional Pain Syndrome (83.9%). Pain clinics administered ketamine via intravenous infusions (96.8%), iontophoresis (61.3%), subcutaneous (3.2%) or oral administration (3.2%). Intravenous ketamine treatment was offered in an inpatient setting in 14 pain clinics, in both an inpatient and outpatient setting in 11 pain clinics and in six pain clinics in an outpatient setting. In the outpatient setting, the median starting dose was 5 mg/h (IQR=17.5-5). The median maximum dose was 27.5 mg/h (IQR=100-11.9). The median infusion duration was 6 h (IQR=8-4). In the inpatient setting, the median starting dose was 5 mg/h (IQR=5-1.5) and the median maximum dose was 25 mg/h (IQR=25-14). Patients were admitted to hospital for a median of 4 days (IQR=5-1).

CONCLUSIONS

The results of this Dutch nationwide survey study show that there are heterogeneous treatment protocols with different indications, treatment setting and dosing regimen for the treatment of chronic pain with ketamine. This study encourages the formulation of a broader consensus and the development of evidence based guidelines for ketamine treatment.

Recreational ketamine-related deaths notified to the National Programme on Substance Abuse Deaths, England, 1997-2019

BACKGROUND

Ketamine is a phencyclidine derivative with dissociative anaesthetic properties. Increasing numbers of individuals in England take ketamine recreationally. Information on deaths arising from such use in England is presented.

METHODS

Cases were extracted on 31 January 2020 from the National Programme on Substance Abuse Deaths database, based on text searches of the cause of death, coroner's verdict and positive toxicology results for the terms 'ketamine' or 'norketamine'.

FINDINGS

During 1997-2005, there were <5 deaths p.a. in which ketamine was implicated. Numbers increased until 2009 (21), plateauing until 2016; thereafter, deaths have risen to about 30 p.a. Decedents' characteristics (N = 283): male 84.1%, mean age 31.2 (SD 10.0) years, employed 56.5%, drug use history 79.6% and living with others 60.3%. Ketamine was detected with other substances in most cases. Main (74.6%) underlying cause of death was accidental poisoning. Ketamine may have impaired judgement in other cases.

CONCLUSIONS

Although controlled, recreational ketamine use and related fatalities continue to increase. Consumers need to be more aware of the potentially fatal risks they face.

Repeated or Continuous Medically Supervised Ketamine Administration Associated with Hepatobiliary Adverse Events: A Retrospective Case Series

Introduction

Emerging off-label medical uses of ketamine for the treatment of persistent conditions such as depression and chronic pain often require repeated administration. Cases reported by other countries suggest that long-term and repeated exposure to ketamine may be associated with several risks, including but not limited to hepatobiliary damage.

Objective

We aimed (1) to characterize the association between repeated administration of ketamine for off-label medical use and hepatobiliary events and (2) to describe recent trends in the use of ketamine across different clinical settings.

Methods

We conducted a retrospective case series analysis, utilizing reports identified from the US Food and Drug Administration Adverse Event Reporting System database as well as the medical literature. We included all cases reported through July 2018 describing both repeated exposure to ketamine in a hospital or ambulatory setting and a hepatobiliary adverse event. We excluded cases describing ketamine abuse. We identified adverse hepatobiliary events using the Medical Dictionary for Regulatory Activities (MedDRA^®) and summarized various case characteristics including: patient demographics, route of ketamine administration, dose, time to onset of event, type of event, and pre-existing risk factors for hepatobiliary disease. To assess trends in the demand for ketamine, we used IQVIA, National Sales Perspectives™ to provide the nationally estimated number of vials sold for ketamine from the manufacturer to all US channels of distribution from 2013 through 2017.

Results

We identified 14 unique cases that met selection criteria with 21 hepatobiliary adverse events including liver enzyme elevation in all cases, biliary dilation with liver cirrhosis (n = 1), biliary dilation with cholangitis (n = 1), and pericholeductal fibrosis (n = 1). Most cases received ketamine for the treatment of complex regional pain syndrome or chronic pain. In cases with a reported time to onset, the majority of events occurred within 4 days. The nationally estimated number of ketamine vials sold in the USA from manufacturers to various channels of distribution increased from 1.2 million in 2013 to 2.1 million in 2017.

Conclusions

We report an association between repeated or continuous administration of ketamine and hepatobiliary adverse events. Increased awareness among clinicians may mitigate these adverse outcomes, especially in the context of growing ketamine sales.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40264-021-01120-9.

The effects of a multiday (10-14 days) subanesthetic dose IV ketamine infusion in the treatment of refractory chronic pain

Aim: Ketamine is an anesthetic agent that at lower doses can be a potent analgesic. There has been an interest in the use of low dose ketamine in treatment of chronic pain syndromes. Patients & methods: We report the results of a retrospective observational study for patients diagnosed with a chronic noncancer pain syndrome receiving a 2-week continuous subanesthetic IV ketamine infusion. Results & conclusion: We conclude that a 10-14 days of subanesthetic ketamine infusion in chronic patients results in clinically significant lowering of patients' numerical pain score. Further studies looking at subanesthetic ketamine infusion in a prospective trial of multi-day IV ketamine infusion in chronic refractory chronic neuropathic pain are needed to further assess the efficacy of ketamine.

Efficacy of ketamine in relieving neuropathic pain: a systematic review and meta-analysis of animal studies

ABSTRACT

In humans, proof of long-term efficacy of ketamine treatment in neuropathic pain is lacking. To improve our understanding of ketamine behavior under various administration conditions, we performed a systematic review and meta-analyses of controlled studies on the efficacy of ketamine in mice and rats with a disease model of nerve injury on relief of allodynia. Searches in PubMed and EMBASE identified 31 unique studies. Four meta-analyses were conducted. The first analysis included 19 comparisons on a single ketamine dose and measurement of effect within 3 hours of dosing and showed an appreciable effect (standardized mean difference 1.6, 95% confidence interval 1.1-2.1). Subgroup analyses showed no effect of species, administration route, or dose. A single administration was insufficient to sustain relief of allodynia at 24 or 72 hours after dosing, as observed in our second analysis (7 comparisons) with similar effects in ketamine-treated and control animals. Chronic ketamine administration (9 comparisons) caused profound relief of allodynia when tested during ketamine exposure (effect size 5.1, 3.7-6.5). The final analysis (6 comparisons) showed that chronic administration caused a slow loss of relief of allodynia with 70% loss of effect 24 days after end of treatment. No subgroups analyses were possible in the last 3 meta-analyses due to small group sizes. These results indicate long-term ketamine anti-allodynic effects after chronic exposure (>3 days) but not after a single administration. Given several limitations, extrapolation of the animal data to the human condition is tenuous.

Efficacy and Tolerability of Oral Compared with Sublingual Ketamine Lozenges as Rescue Analgesics in Adults for Acute Pain: The OSKet Trial

BACKGROUND AND OBJECTIVE

Ketamine is an N-methyl-D-aspartate receptor (NMDA) antagonist used widely as an intravenous analgesic for treatment of acute pain. Its use as oral and sublingual analgesics is not well studied. This study aims to compare the clinical efficacy and tolerability of oral (PO) versus sublingual (SL) ketamine lozenges in adult patients with moderate-to-severe breakthrough pain.

METHODS

The study had a randomized, double-blind crossover design in 23 inpatients requiring ketamine as rescue analgesics when pain scores exceeded 4/10 on the Numerical Rating Scales. Each participant received either SL 50 mg ketamine lozenge and PO placebo lozenge or SL placebo lozenge and PO 50 mg ketamine lozenge in two treatment periods with a minimum 24-h washout. Pain scores and adverse effects were documented half hourly for the first 2 h, then one hourly for the next 2 h after treatment. The time to first effect and time to meaningful pain relief were recorded. Patients reported their satisfaction and a global impression of change (GIC) at the end of each treatment period. Data were analysed using random effects regression models.

RESULTS

Sixteen subjects completed both days, 7 completed 1 day. Time to first effect was 13.1 min PO versus 6.6 min SL (p = 0.069), time to meaningful pain relief was 29.4 min PO versus 10.8 min SL (p = 0.02). Pain scores were not significantly different at all time points post-treatment. Satisfaction and GIC scores were similar for both groups. Overall, adverse events occurred more often with SL administration (p = 0.02).

CONCLUSIONS

Sublingual administration of ketamine led to a faster onset of pain relief (but also a higher adverse event rate), but in all other aspects treatment with ketamine given sublingually and orally produced similar analgesic effects.

ACTRN

ACTRN12621000240842, 08/03/2021, retrospectively registered.

CYP2B6 Functional Variability in Drug Metabolism and Exposure Across Populations-Implication for Drug Safety, Dosing, and Individualized Therapy

Adverse drug reactions (ADRs) are one of the major causes of morbidity and mortality worldwide. It is well-known that individual genetic make-up is one of the causative factors of ADRs. Approximately 14 million single nucleotide polymorphisms (SNPs) are distributed throughout the entire human genome and every patient has a distinct genetic make-up which influences their response to drug therapy. Cytochrome P450 2B6 (CYP2B6) is involved in the metabolism of antiretroviral, antimalarial, anticancer, and antidepressant drugs. These drug classes are commonly in use worldwide and face specific population variability in side effects and dosing. Parts of this variability may be caused by single nucleotide polymorphisms (SNPs) in the CYP2B6 gene that are associated with altered protein expression and catalytic function. Population variability in the CYP2B6 gene leads to changes in drug metabolism which may result in adverse drug reactions or therapeutic failure. So far more than 30 non-synonymous variants in CYP2B6 gene have been reported. The occurrence of these variants show intra and interpopulation variability, thus affecting drug efficacy at individual and population level. Differences in disease conditions and affordability of drug therapy further explain why some individuals or populations are more exposed to CYP2B6 pharmacogenomics associated ADRs than others. Variabilities in drug efficacy associated with the pharmacogenomics of CYP2B6 have been reported in various populations. The aim of this review is to highlight reports from various ethnicities that emphasize on the relationship between CYP2B6 pharmacogenomics variability and the occurrence of adverse drug reactions. In vitro and in vivo studies evaluating the catalytic activity of CYP2B6 variants using various substrates will also be discussed. While implementation of pharmacogenomic testing for personalized drug therapy has made big progress, less data on pharmacogenetics of drug safety has been gained in terms of CYP2B6 substrates. Therefore, reviewing the existing evidence on population variability in CYP2B6 and ADR risk profiles suggests that, in addition to other factors, the knowledge on pharmacogenomics of CYP2B6 in patient treatment may be useful for the development of personalized medicine with regards to genotype-based prescription.

Interplay between Gating and Block of Ligand-Gated Ion Channels

Drugs that inhibit ion channel function by binding in the channel and preventing current flow, known as channel blockers, can be used as powerful tools for analysis of channel properties. Channel blockers are used to probe both the sophisticated structure and basic biophysical properties of ion channels. Gating, the mechanism that controls the opening and closing of ion channels, can be profoundly influenced by channel blocking drugs. Channel block and gating are reciprocally connected; gating controls access of channel blockers to their binding sites, and channel-blocking drugs can have profound and diverse effects on the rates of gating transitions and on the stability of channel open and closed states. This review synthesizes knowledge of the inherent intertwining of block and gating of excitatory ligand-gated ion channels, with a focus on the utility of channel blockers as analytic probes of ionotropic glutamate receptor channel function.

Pathophysiologic Approach to Pain Therapy for Complex Pain Entities: A Narrative Review

Pain management is challenging for both clinicians and patients. In fact, pain patients are frequently undertreated or even completely untreated. Optimal treatment is based on targeting the underlying mechanisms of pain and tailoring the management modality for each patient using a personalized approach. This narrative review deals with pain conditions that have a complex underlying mechanism and need an individualized and frequently multifactorial approach to pain management. The research is based on previously conducted studies, and does not contain any studies with human participants or animals performed by any of the authors. This is not an exhaustive review of the current evidence. However, it provides the clinician with a perspective on pain therapy targeting the underlying pain mechanism(s). When dealing with complex pain conditions, the prudent physician benefits from having a deep knowledge of various underlying pain mechanisms in order to provide a plan for optimal pharmacological pain relief to patients.

S-Ketamine's Effect Changes the Cortical Electrophysiological Activity Related to Semantic Affective Dimension of Pain: A Placebo- Controlled Study in Healthy Male Individuals

Background

Previous studies using the electroencephalogram (EEG) technique pointed out that ketamine decreases the amplitude of cortical electrophysiological signal during cognitive tasks, although its effects on the perception and emotional-valence judgment of stimuli are still unknown.

Objective

We evaluated the effect of S-ketamine on affective dimension of pain using EEG and behavioral measures. The hypothesis was that S-ketamine would be more effective than placebo, both within and between groups, to attenuate the EEG signal elicited by target and non-target words.

Methods

This double-blind parallel placebo-controlled study enrolled 24 healthy male volunteers between 19 and 40 years old. They were randomized to receive intravenous S-ketamine (n = 12) at a plasmatic concentration of 60 ng/ml or placebo (n = 12). Participants completed a computerized oddball paradigm containing written words semantically related to pain (targets), and non-pain related words (standard). The volunteers had to classify the words either as “positive,” “negative” or “neutral” (emotional valence judgment). The paradigm consisted in 6 blocks of 50 words each with a fixed 4:1 target/non-target rate presented in a single run. Infusion started during the interval between the 3rd and 4th blocks, for both groups. EEG signal was registered using four channels (Fz, Pz, Pz, and Oz, according to the 10–20 EEG system) with a linked-earlobe reference. The area under the curve (AUC) of the N200 (interval of 100–200 ms) and P300 (300–500 ms) components of event-related potentials (ERPs) was measured for each channel.

Results

S-ketamine produced substantial difference (delta) in the AUC of grand average ERP components N200 (P = 0.05) and P300 (P = 0.02) at Pz during infusion period when compared to placebo infusion for both targets and non-targets. S-ketamine was also associated with a decrease in the amount of pain-related words judged as negative from before to after infusion [mean = 0.83 (SD = 0.09) vs. mean = 0.73 (SD = 0.11), respectively; P = 0.04].

Conclusion

Our findings suggest that S-ketamine actively changed the semantic processing of written words. There was an increase in electrophysiological response for pain-related stimuli and a decrease for standard stimuli, as evidenced by the increased delta of AUCs. Behaviorally, S-ketamine seems to have produced an emotional and discrimination blunting effect for pain-related words.

Clinical Trial Registration

www.ClinicalTrials.gov, identifier NCT03915938.

Assessment of Ketamine Adult Anesthetic Doses in Pediatrics Using Pharmacokinetic Modeling and Simulations

BACKGROUND

Although few studies have used ketamine for induction and maintenance of pediatric anesthesia, official dosage recommendations are lacking. This study evaluates the outcomes of adult anesthetic doses in a pediatric population through pharmacokinetic modeling and computer simulations in an attempt to recommend an adequate ketamine dosing regimen.

METHODS

Ketamine plasma concentration-time data in 19 children (age 8 months to 16 years; weight 5.5 to 67 kg) were analyzed according to a non-compartmental pharmacokinetic approach. The relationship between pharmacokinetic parameters and demographic covariates was mathematically characterized. A one-compartment open model was implemented to simulate the plasma profile following administration of 1-4.5 mg/kg IV bolus dose and 0.1-0.5 mg/kg/min continuous infusion of ketamine and to predict anesthesia onset and offset.

KEY RESULTS

Pharmacokinetic parameters determined were clearance 0.025 ± 0.008 L/kg/min; distribution volume 3.3 ± 1.3 L/kg; half-life 2.6 ± 1 h; and mean residence time 2.3 ± 0.64 h. Body weight was the best predictor of clearance and distribution volume according to a 0.75-power model. Using weight to scale doses was associated with limited variability in simulated concentrations. Ketamine administered as 2.25 mg/kg IV bolus dose, followed by 0.1 mg/kg/min continuous IV infusion enables anesthesia initiation within 3 minutes and maintains it for 3 hours.

CONCLUSIONS & INFERENCES

Weight-based dosing minimizes age-dependent variation in the plasma concentration of ketamine. Low-to-intermediate adult doses are suitable for induction and maintenance of safe anesthesia in children undergoing short-term surgical operations. However, this finding requires validation in controlled clinical trials before it is adopted into surgical standard practices.

Ten-Hour Exposure to Low-Dose Ketamine Enhances Corticostriatal Cross-Frequency Coupling and Hippocampal Broad-Band Gamma Oscillations

Introduction: Treatment-resistant depression, post-traumatic stress disorder, chronic pain, and L-DOPA-induced dyskinesia in Parkinson’s disease are characterized by hypersynchronous neural oscillations. Sub-anesthetic ketamine is effective at treating these conditions, and this may relate to ketamine’s capacity to reorganize oscillatory activity throughout the brain. For example, a single ketamine injection increases gamma (∼40 Hz) and high-frequency oscillations (HFOs, 120–160 Hz) in the cortex, hippocampus, and striatum. While the effects of single injections have been investigated, clinical ketamine treatments can involve 5-h up to 3-day sub-anesthetic infusions. Little is known about the effects of such prolonged exposure on neural synchrony. We hypothesized that hours-long exposure entrains circuits that generate HFOs so that HFOs become sustained after ketamine’s direct effects on receptors subside.

Methods: Local-field recordings were acquired from motor cortex (M1), striatum, and hippocampus of behaving rats (n = 8), and neural responses were measured while rats received 5 ketamine injections (20 mg/kg, i.p., every 2 h, 10-h exposure). In a second experiment, the same animals received injections of D1-receptor antagonist (SCH-23390, 1 mg/kg, i.p.) prior to ketamine injection to determine if D1 receptors were involved in producing HFOs.

Results: Although HFOs remained stable throughout extended ketamine exposure, broad-band high-frequency activity (40–140 Hz) in the hippocampus and delta-HFO cross-frequency coupling (CFC) in dorsal striatum increased with the duration of exposure. Furthermore, while ketamine-triggered HFOs were not affected by D1 receptor blockade, ketamine-associated gamma in motor cortex was suppressed, suggesting involvement of D1 receptors in ketamine-mediated gamma activity in motor cortex.

Conclusion: Prolonged ketamine exposure does not enhance HFOs in corticostriatal circuits, but, instead, enhances coordination between low and high frequencies in the striatum and reduces synchrony in the hippocampus. Increased striatal CFC may facilitate spike-timing dependent plasticity, resulting in lasting changes in motor activity. In contrast, the observed wide-band high-frequency “noise” in the hippocampus suggests that ketamine disrupts action-potential timing and reorganizes connectivity in this region. Differential restructuring of corticostriatal and limbic circuits may contribute to ketamine’s clinical 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.

Effects of Subanesthetic Ketamine Administration on Visual and Auditory Event-Related Potentials (ERP) in Humans: A Systematic Review

Ketamine is a non-competitive N-Methyl-D-Aspartate (NMDA) receptor antagonist whose effect in subanesthetic doses has been studied for chronic pain and mood disorders treatment. It has been proposed that ketamine could change the perception of nociceptive stimuli by modulating the cortical connectivity and altering the top-down mechanisms that control conscious pain perception. As this is a strictly central effect, it would be relevant to provide fresh insight into ketamine's effect on cortical response to external stimuli. Event-related potentials (ERPs) reflect the combined synchronic activity of postsynaptic potentials of many cortical pyramidal neurons similarly oriented, being a well-established technique to study cortical responses to sensory input. Therefore, the aim of this study was to examine the current evidence of subanesthetic ketamine doses on patterns of cortical activity based on ERPs in healthy subjects. To answer the question whether ERPs could be potential markers of the cortical effects of ketamine, we conducted a systematic review of ketamine's effect on ERPs after single and repeated doses. We have searched PubMed, EMBASE and Cochrane Databases and pre-selected 141 articles, 18 of which met the inclusion criteria. Our findings suggest that after ketamine administration some ERP parameters are reduced (reduced N2, P2, and P3 amplitudes, PN and MMN) while others remain stable or are even increased (P50 reduction, PPI, P1, and N1 amplitudes). The current understanding of these effects is that ketamine alters the perceived contrast between distinct visual and auditory stimuli. The analgesic effect of ketamine might also be influenced by a decreased affective discrimination of sensorial information, a finding from studies using ketamine as a model for schizophrenia, but that can give an important hint not only for the treatment of mood disorders, but also to treat pain and ketamine abuse.

Ketamine for cancer pain: what is the evidence?

PURPOSE OF REVIEW

In this review, we assess the benefit of ketamine in the treatment of terminal cancer pain that is refractory to opioid treatment and/or complicated by neuropathy.

RECENT FINDINGS

While randomized controlled trials consistently show lack of clinical efficacy of ketamine in treating cancer pain, a large number of open-label studies and case series show benefit.

SUMMARY

Ketamine is an N-methyl-D-aspartate receptor antagonist that at low-dose has effective analgesic properties. In cancer pain, ketamine is usually prescribed as adjuvant to opioid therapy when pain becomes opioid resistant or when neuropathic pain symptoms dominate the clinical picture. A literature search revealed four randomized controlled trials that examined the benefit of oral, subcutaneous or intravenous ketamine in opioid refractory cancer pain. None showed clinically relevant benefit in relieving pain or reducing opioid consumption. This suggests absence of evidence of benefit for ketamine as adjuvant analgesic in cancer pain. These findings contrast the benefit from ketamine observed in a large number of open-label studies and (retrospective) case series. We relate the opposite outcomes to methodological issues. The complete picture is such that there is still insufficient evidence to state with certainty that ketamine is not effective in cancer pain.

Ketamine for pain

The efficacy of the N-methyl-D-aspartate receptor antagonist ketamine as an analgesic agent is still under debate, especially for indications such as chronic pain. To understand the efficacy of ketamine for relief of pain, we performed a literature search for relevant narrative and systematic reviews and meta-analyses. We retrieved 189 unique articles, of which 29 were deemed appropriate for use in this review. Ketamine treatment is most effective for relief of postoperative pain, causing reduced opioid consumption. In contrast, for most other indications (that is, acute pain in the emergency department, prevention of persistent postoperative pain, cancer pain, and chronic non-cancer pain), the efficacy of ketamine is limited. Ketamine's lack of analgesic effect was associated with an increase in side effects, including schizotypical effects.

Case Study of High-Dose Ketamine for Treatment of Complex Regional Pain Syndrome in the Pediatric Intensive Care Unit

Complex regional pain syndrome (CRPS) is a life-altering and debilitating chronic pain condition. The authors are presenting a case study of a female who received high-dose ketamine for the management of her CRPS. The innovative treatment lies not only within the pharmacologic management of her pain, but also in the fact that she was the first patient to be admitted to our pediatric intensive care unit solely for pain control. The primary component of the pharmacotherapy treatment strategy plan was escalating-dose ketamine infusion via patient-controlled-analgesia approved by the pharmacy and therapeutics committee guided therapy for this patient. The expertise of advanced practice nurses blended exquisitely to ensure patient and family-centered care and the coordination of care across the illness trajectory. The patient experienced positive outcomes.

Reduction of central neuropathic pain with ketamine infusion in a patient with Ehlers-Danlos syndrome: a case report

Objective

Ehlers–Danlos syndrome frequently causes acute and chronic pain because of joint subluxations and dislocations secondary to hypermobility. Current treatments for pain related to Ehlers–Danlos syndrome and central pain syndrome are inadequate. This case report discusses the therapeutic use of ketamine intravenous infusion as an alternative.

Case report

A 27-year-old Caucasian female with a history of Ehlers–Danlos syndrome and spinal cord ischemic myelopathy resulting in central pain syndrome, presented with severe generalized body pain refractory to multiple pharmacological interventions. After a 7-day course of ketamine intravenous infusion under controlled generalized sedation in the intensive care unit, the patient reported a dramatic reduction in pain levels from 7–8 out of 10 to 0–3 out of 10 on a numeric rating scale and had a significant functional improvement. The patient tolerated a reduction in her pain medication regimen, which originally included opioids, gabapentin, pregabalin, tricyclic antidepressants, and nonsteroidal anti-inflammatory drugs.

Conclusion

Ketamine infusion treatment has been used in various pain syndromes, including central neuropathic pain, ischemic pain, and regional pain syndrome. Reports have suggested that ketamine modulates pain by the regression of N-methyl-D-aspartate receptor to a resting state. As such, propagation of nociceptive signal to brain is interrupted allowing for the restoration of physiological balance between pain inhibition and facilitation. The present report shows that this treatment option can be used in patients with refractory central pain syndrome in the setting of spinal cord myelopathy secondary to Ehlers–Danlos syndrome. In addition, as seen in this case, this protocol can potentially decrease the chronic use of pain medication, such as opioids.

Effects of low-dose ketamine on succinylcholine-induced postoperative myalgia in outpatient surgeries: a randomized, double-blind study

Objective

Despite the many complications of succinylcholine, it is still widely used as a superior muscle relaxant for rapid sequence induction. One of these complications is postoperative myalgia (POM). The aim of this study was to investigate the prophylactic effect of low-dose ketamine on the incidence and severity of POM.

Materials and methods

In this double-blind clinical study, a total of 148 patients scheduled for general anesthesia were randomly divided into two equal groups. Initially, in Group K, 0.5 mg/kg of ketamine was injected intravenously, whereas in Group N, the same volume (5 mL) of normal saline was injected. Thereafter, anesthesia was induced in all patients, by injecting 1.5 mg/kg of fentanyl and 2 mg/kg of propofol intravenously. Following the loss of eyelid reflex, 1.5 mg/kg of succinylcholine was injected intravenously as a muscle relaxant and then the patients were intubated. POM was defined as a pain with no surgical interferences, and its intensity was graded based on a four-point scale. The incidence and severity of myalgia were assessed by a blinded observer 24 hours after surgery.

Results

In terms of demographic data, the results of this study showed that there is no significant difference between patients in both groups (P>0.05). Overall, the incidence of POM in Group K was significantly less, when compared with Group N (P<0.05), but both groups were comparable based on the grade 2 of POM. After the induction of anesthesia, the systolic and diastolic blood pressure values were found to reduce in both groups (P<0.05). However, the changes were somehow similar, and repeated measures of variance analysis showed no significant difference in the two study groups (P>0.05).

Conclusion

The addition of 0.5 mg/kg of ketamine to propofol for the induction of anesthesia can be effective in reducing the incidence of low-grade POM.

Role of ketamine for analgesia in adults and children

Ketamine an N-methyl-D-aspartate (NMDA) receptor blocking agent and a dissociative anesthetic with neurostimulatory side effects. In recent years, multiple research trials as well as systematic reviews and meta-analyses suggest the usefulness of ketamine as a strong analgesic used in subanesthetic intravenous doses, and also as a sedative. In addition, ketamine was noted to possess properties of anti-tolerance, anti-hyperalgesia and anti-allodynia most likely secondary to inhibition of the NMDA receptors. Tolerance, hyperalgesia and allodynia phenomena are the main components of opioid resistance, and pathological pain is often seen in the clinical conditions involving neuropathic pain, opioid-induced hyperalgesia, and central sensitization with allodynia or hyperalgesia. All these conditions are challenging to treat. In low doses, ketamine does not have major adverse dysphoric effects and also has the favorable effects of reduced incidence of opioid-induced nausea and vomiting. Therefore, ketamine can be a useful adjunct for pain control after surgery. Additional studies are required to determine the role of ketamine in the immediate postoperative period after surgical interventions known to produce severe pain and in the prevention and treatment of chronic pain.

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.

Ketamine for pain management in France, an observational survey

CONTEXT

Before updating the French guidelines on postoperative pain treatment in 2015, the Pain Committee of the French Society of Anaesthesiology and Intensive Care (SFAR) conducted a survey on the medical use of ketamine in France.

METHODS

An online questionnaire was nationally distributed to members of SFAR, the French Pain Society (SFETD) and the French Society of Emergency Medicine (SFMU). The questionnaire included questions on demographic data, the type of patients for whom ketamine was prescribed, the doses used, the side effects and safety measures associated with the administration of ketamine.

RESULTS

A total of 1388 questionnaires were analysed. Ninety-two percent of the responders declared that they used ketamine. Ketamine was widely used as anti-hyperalgesic medication but the modalities of administration and the doses varied greatly and were not in accordance with the guidelines. Despite the lack of evidence and guidelines, ketamine has also been used to treat acute and chronic pain. Doses, duration and localization of the patients during administration have varied greatly. Psychedelic effects and hallucinations are the most feared side effects. In terms of monitoring during ketamine infusion, 15% of physicians declared that no monitoring was necessary while 59%, 55%, 59% and 77% monitored heart rate, SpO2, blood pressure and level of consciousness, respectively.

CONCLUSION

Anaesthesiologists have integrated the benefit of ketamine in preventing hyperalgesia but there is no consensus on doses and duration. For other indications (acute and chronic pain treatment), toxicity and the absence of significant benefit call for guidelines from scientific societies.

Nitrous oxide persistently alleviates pain hypersensitivity in neuropathic rats: A dose-dependent effect

BACKGROUND

Despite numerous pharmacological approaches, there are no common analgesic drugs that produce meaningful relief for the majority of patients with neuropathic pain. Although nitrous oxide (N2O) is a weak analgesic that acts via opioid-dependent mechanisms, it is also an antagonist of the N-methyl-D-aspartate receptor (NMDAR). The NMDAR plays a critical role in the development of pain sensitization induced by nerve injury.

OBJECTIVE

Using the chronic constriction injury of the sciatic nerve in male rats as a preclinical model of neuropathic pain, the first aim of the present study was to evaluate the lowest N2O concentration and the shortest time of N2O postinjury exposure that would produce persistent relief of neuropathic pain. The second aim was to compare the effects of N2O with gabapentin, a reference drug used in human neuropathic pain relief.

METHODS

Changes in the nociceptive threshold were evaluated using the paw pressure vocalization test in rats.

RESULTS

Among the various N2O concentrations tested, which ranged from 25% to 50%, only 50% N2O single exposure for 1 h 15 min induced a persistent (minimum of three weeks) and significant (60%) reduction in pain hypersensitivity. A single gabapentin dose (75 mg⁄kg to 300 mg⁄kg, intraperitoneally) induced an acute (1 h to 1 h 30 min) dose-dependent effect, but not a persistent effect such as that observed with N2O.

CONCLUSIONS

These preclinical results suggest that N2O is advantageous for long-lasting neuropathic pain relief after sciatic nerve injury compared with other drugs used in humans such as gabapentinoids or NMDAR antagonists. The present preclinical study provides a rationale for developing comparative clinical studies.

CYP2B6*6 allele and age substantially reduce steady-state ketamine clearance in chronic pain patients: impact on adverse effects

AIMS

Ketamine analgesia is limited by low intrinsic efficacy compounded by large interindividual variability in drug responses, possibly due to the heterogeneity in drug concentration. The CYP2B6*6 allele is associated with substantially reduced ketamine metabolism in vitro and, therefore, may affect ketamine clearance. Our aims were to examine the impact of the CYP2B6*6 allele on ketamine plasma clearance and on adverse effects in chronic pain patients.

METHODS

CYP2B6 genotypes were identified in 49 chronic pain patients who received 24 h continuous subcutaneous infusions of ketamine. Steady-state plasma concentrations of ketamine (Css,k ) and norketamine (Css,nk ) were determined using HPLC.

RESULTS

The median plasma clearance of ketamine after 100 mg 24 h(-1) dose was significantly lower in patients with the CYP2B6*6/*6 (21.6 l h(-1) ) and CYP2B6*1/*6 (40.6 l h(-1) ) genotypes compared with patients with the CYP2B6*1/*1 genotype (68.1 l h(-1) , P < 0.001). The ketamine : norketamine plasma metabolic ratio was significantly higher in patients with the CYP2B6*6/*6 genotype than in those with the CYP2B6*1/*6 and the CYP2B6*1/*1 genotypes (P < 0.001). Patients who experienced adverse effects had lower plasma clearance (45.6 l h(-1) ) than those who did not (52.6 l h(-1) , P = 0.04). The CYP2B6*6 genotype and age, and their combined impact explained 40%, 30% and 60% of the variation in Css,k , respectively. Similar results were observed after higher doses.

CONCLUSIONS

The CYP2B6*6 allele is associated with a substantial decrease in steady-state ketamine plasma clearance in chronic pain patients. The decreased clearance and resultant higher plasma concentrations may be associated with a higher incidence of ketamine adverse effects.

Study protocol for a randomised, double-blinded, placebo-controlled, clinical trial of S-ketamine for pain treatment in patients with chronic pancreatitis (RESET trial)

INTRODUCTION

Chronic pancreatitis (CP) is an inflammatory disease that causes irreversible damage to pancreatic tissue. Pain is its most prominent symptom. In the absence of pathology suitable for endoscopic or surgical interventions, pain treatment usually includes opioids. However, opioids often have limited efficacy. Moreover, side effects are common and bothersome. Hence, novel approaches to control pain associated with CP are highly desirable. Sensitisation of the central nervous system is reported to play a key role in pain generation and chronification. Fundamental to the process of central sensitisation is abnormal activation of the N-methyl-D-aspartate receptor, which can be antagonised by S-ketamine. The RESET trial is investigating the analgaesic and antihyperalgesic effect of S-ketamine in patients with CP.

METHODS AND ANALYSIS

40 patients with CP will be enrolled. Patients are randomised to receive 8 h of intravenous S-ketamine followed by oral S-ketamine, or matching placebo, for 4 weeks. To improve blinding, 1 mg of midazolam will be added to active and placebo treatment. The primary end point is clinical pain relief as assessed by a daily pain diary. Secondary end points include changes in patient-reported outcome measures, opioid consumption and rates of side effects. The end points are registered through the 4-week medication period and for an additional follow-up period of 8 weeks to investigate long-term effects. In addition, experimental pain measures also serves as secondary end points, and neurophysiological imaging parameters are collected. Furthermore, experimental baseline recordings are compared to recordings from a group of healthy controls to evaluate general aspects of pain processing in CP.

ETHICS AND DISSEMINATION

The protocol is approved by the North Denmark Region Committee on Health Research Ethics (N-20130040) and the Danish Health and Medicines Authorities (EudraCT number: 2013-003357-17). The results will be disseminated in peer-reviewed journals and at scientific conferences.

TRIAL REGISTRATION NUMBER

The study is registered at http://www.clinicaltrialsregister.eu (EudraCT number 2013-003357-17).

Efficacy and safety of oral ketamine for the relief of intractable chronic pain: A retrospective 5-year study of 51 patients

BACKGROUND

This work summarizes the efficiency, failures and adverse effects of oral administration of ketamine at home for intractable pain.

METHODS

This 5-year retrospective study involved testing ketamine by intravenous in-hospital administration, then a conversion to an oral route, or oral treatment directly administered at home. The daily intravenous dose was increased by steps of 0.5 mg/kg to attain an effective daily dose of 1.5-3.0 mg/kg. Pain was evaluated on a numeric scale from 0 to 10, and evidence of adverse effects was collected every day. The effective daily dose was delivered orally (three to four intakes). If effective, ketamine was continued for 3 months. Short infusions or direct oral treatment began with a 0.5-mg/kg dose, then the daily ketamine dose was increased in 15- to 20-mg increments.

RESULTS

Among 55 cases (51 patients, neuropathic pain 60%), the mean effective oral dose was 2 mg/kg. Ketamine was effective in 24 patients (44%, mean pain reduction 67 ± 17%), partially effective in 20% (mean pain reduction 30 ± 11%), with a mean opioid sparing of 63 ± 32%, and failure in 22%. Half of the patients experienced adverse effects, but only eight had to stop treatment. For patients with opioid therapy, failure of ketamine was less frequent (7% vs. 36%; p < 0.02), with fewer adverse effects (33% vs. 68%; p < 0.01).

CONCLUSIONS

Pain was reduced or abolished in two-thirds of patients under ketamine therapy; ketamine was effective for patients taking opioids and resulted in few adverse effects.

Ketamine for chronic pain: risks and benefits

The anaesthetic ketamine is used to treat various chronic pain syndromes, especially those that have a neuropathic component. Low dose ketamine produces strong analgesia in neuropathic pain states, presumably by inhibition of the N-methyl-D-aspartate receptor although other mechanisms are possibly involved, including enhancement of descending inhibition and anti-inflammatory effects at central sites. Current data on short term infusions indicate that ketamine produces potent analgesia during administration only, while three studies on the effect of prolonged infusion (4-14 days) show long-term analgesic effects up to 3 months following infusion. The side effects of ketamine noted in clinical studies include psychedelic symptoms (hallucinations, memory defects, panic attacks), nausea/vomiting, somnolence, cardiovascular stimulation and, in a minority of patients, hepatoxicity. The recreational use of ketamine is increasing and comes with a variety of additional risks ranging from bladder and renal complications to persistent psychotypical behaviour and memory defects. Blind extrapolation of these risks to clinical patients is difficult because of the variable, high and recurrent exposure to the drug in ketamine abusers and the high frequency of abuse of other illicit substances in this population. In clinical settings, ketamine is well tolerated, especially when benzodiazepines are used to tame the psychotropic side effects. Irrespective, close monitoring of patients receiving ketamine is mandatory, particularly aimed at CNS, haemodynamic, renal and hepatic symptoms as well as abuse. Further research is required to assess whether the benefits outweigh the risks and costs. Until definite proof is obtained ketamine administration should be restricted to patients with therapy-resistant severe neuropathic pain.

Psychiatric side effects of ketamine in hospitalized medical patients administered subanesthetic doses for pain control

OBJECTIVE

To assess the psychiatric side effects of ketamine when administered in subanesthetic doses to hospitalized patients. It is hypothesized that such effects occur frequently.

METHODS

In this retrospective study, the medical records of 50 patients hospitalized on medical and surgical units at our facility who had continuous intravenous infusions of ketamine for pain or mild sedation were reviewed. Patient progress in the days following the start of ketamine infusion was reviewed and response to ketamine was noted.

RESULTS

Twenty-two percent of the patients were noted to have some type of psychiatric reaction to ketamine, including agitation, confusion, and hallucinations. These reactions were relatively short lived, namely, occurring during or shortly after the infusions. No association was found between patient response to ketamine and gender, age, or infusion rate.

CONCLUSION

Awareness of the psychiatric side effects of ketamine is an important consideration for clinicians administering this medication either for pain control or for depressive illness.