Pharmacokinetic and pharmacodynamic considerations for NMDA-receptor antagonist ketamine in the treatment of chronic neuropathic pain: an update of the most recent literature

Insights for the Next Generation of Ketamine for the Treatment of Depressive Disorder

Treatment-resistant depression responds quickly to ketamine. As an N-methyl-d-aspartate receptor (NMDAR) antagonist, ketamine may affect prefrontal cortex (PFC) neurons. Recent investigations reveal that the (R)-enantiomer is the most effective and least abuseable antidepressant. The Food and Drug Administration approves only the (S)-enantiomer for medical usage. (2R,6R)-Hydroxynorketamine (HNK) inhibits mGlu2, linked to a Gi, in presynaptic glutamatergic neurons, increasing brain-derived neurotrophic factor (BDNF) release, which autocrinely activates Tropomyosin receptor kinase B (TrkB) and promotes synaptogenesis. Ketamine, originally an anesthetic, has garnered attention for its many pharmacological effects, including its potential as a rapid-acting antidepressant and recreational use. In this Perspective, we explore the synthesis, pharmacology, metabolism, and effects of ketamine and its metabolites in animal and human studies to explain the difference in the biological activity between the enantiomers.

Effect of a constant rate infusion of ketamine on left ventricular systolic and diastolic function in dogs anesthetized with propofol

OBJECTIVE

To evaluate the effect of a constant rate infusion of ketamine on left ventricular systolic and diastolic function in dogs anesthetized with propofol.

STUDY DESIGN

Prospective randomized, blinded clinical study.

ANIMALS

Sixteen healthy dogs.

METHODS

Dogs were randomized into two groups, the propofol-ketamine group (GPK) and propofol group (GP), with eight animals each. Anesthesia was induced with propofol and maintained with a constant rate infusion (CRI) of propofol at a rate of 0.8 mg/kg/min. All dogs were mechanically ventilated throughout the study. Thirty-five minutes after anesthesia started, the GPK received a bolus of ketamine (0.5 mg/kg IV, over 2 minutes) followed by the CRI of ketamine at 30 μg/kg/min, while the GP received the same volume of 0.9% NaCl over 2 minutes followed by the CRI of 0.9% NaCl at the same rate. Hemodynamic and echocardiographic variables were recorded 15 min after initiating CRI of propofol (M0), immediately after each treatment bolus (M1), and 20 (M2) and 40 min (M3) after initiating CRI of ketamine or 0.9% NaCl solution in both groups.

RESULTS

Cardiac index, stroke index, and peripheral vascular resistance index were not significantly different between treatments. No significant differences in left ventricular systolic and diastolic functions derived from echocardiographic variables were observed between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

During treatment with CRI of ketamine at the proposed rate, hemodynamic parameters and echocardiographic variables, used to measure left ventricular systolic and diastolic function, were maintained stable in healthy dogs anesthetized with propofol.

Esketamine use for primary intelligent analgesia in adults with severe burns: A double-blind randomized trial with effects on analgesic efficacy, gastrointestinal function and mental state

BACKGROUND

Opioid consumption for analgesia in burn patients is enormous. Non-opioid analgesics for burn pain management may result in opioid sparing, reducing opioid-related adverse reactions and drug tolerance or addiction.

METHODS

A dual-center, randomized controlled trial assessed Esketamine for the perioperative period in patients with severe [20-50 % total body surface area (TBSA)] and extensive (≥ 50 % TBSA) burns, comparing analgesia with standard anesthesia. Sixty patients were randomly allocated (1:1 ratio) to two arms. In the Treatment Arm, patients received intra-operative Esketamine and postoperative intravenous primary intelligent analgesia pump with Esketamine. Patients in the Control Arm received the same intervention as Treatment Arm without Esketamine. The primary endpoint was subjective analgesic efficacy (SAE) evaluated on Day 28 or the day before hospital discharge. Secondary outcomes included the postoperative Numeric Pain Rating (NPR) Scale at rest (NPRr) and during movement (NPRm) and opioid consumption. Gastrointestinal dysfunction Scores (GIDS) and serum markers of intestinal injury [intestinal fatty acid-binding protein 2 (iFabp2) and apolipoproteinA2 (ApoA2)] were measured in the 1st and 4th post-injury weeks. Depression and sleep quality were assessed by relevant questionnaires.

RESULTS

Fifty-five patients were included in the analysis. Esketamine-treated Arm recorded a better analgesic efficacy than the Control Arm (proportion of patients with Grade 1 or 2 SAE scores, 67.9 % vs. 40.7 %, p = 0.022). Esketamine-treated patients had lower NPRm values (p = 0.033) and lower daily opioid consumption (p = 0.033) when compared with Controls. Esketamine-treated patients showed comparable gastrointestinal recovery to those in the Control Arm. The overall sleep quality might be improved in the Treatment Arm.

CONCLUSIONS

Esketamine use is safe for perioperative primary intelligent analgesia of severe burns, resulting in improved resting pain control and lower opioid requirements.

TRIAL REGISTRATION

The trial was registered at the Chinese Clinical Trial Registry (www.chictr.org.cn/) (ChiCTR2000034069).

Effect of intraoperative injection of esketamine on postoperative analgesia and postoperative rehabilitation after cesarean section

BACKGROUND

Following cesarean section, a significant number of women encounter moderate to severe pain. Inadequate management of acute pain post-cesarean section can have far-reaching implications, adversely impacting maternal emotional well-being, daily activities, breastfeeding, and neonatal care. It may also impede maternal organ function recovery, leading to escalated opioid usage, heightened risk of postpartum depression, and the development of chronic postoperative pain. Both the Chinese Enhanced Recovery After Surgery (ERAS) guidelines and the American ERAS Society guidelines consistently advocate for the adoption of multimodal analgesia protocols in post-cesarean section pain management. Esketamine, functioning as an antagonist of the N-Methyl-D-Aspartate receptor, has been validated for pain management in surgical patients and has exhibited effectiveness in depression treatment. Research has suggested that incorporating esketamine into postoperative pain management via pain pumps can lead to improvements in short-term depression and pain outcomes. This study aims to assess the efficacy and safety of administering a single dose of esketamine during cesarean section.

AIM

To investigate the effect of intraoperative injection of esketamine on postoperative analgesia and postoperative rehabilitation after cesarean section.

METHODS

A total of 315 women undergoing elective cesarean section under combined spinal-epidural anesthesia were randomized into three groups: low-dose esketamine (0.15 mg/kg), high-dose esketamine (0.25 mg/kg), and control (saline). Postoperative Visual Analog Scale (VAS) scores were recorded at 6 hours, 12 hours, 24 hours, and 48 hours. Edinburgh Postnatal Depression Scale (EPDS) scores were noted on 2 days, 7 days and 42 days. Ramsay sedation scores were assessed at specified intervals post-injection. Postoperative adverse reactions were also recorded.

RESULTS

Low-dose group and high-dose group compared to control group, had significantly lower postoperative VAS pain scores at 6 hours 12 hours, and 24 hours (P < 0.05), with reduced analgesic usage (P < 0.05). EPDS scores and postpartum depression rates were significantly lower on 2 days and 7 days (P < 0.05). No significant differences in first exhaust and defecation times were observed (P > 0.05), but ambulation times were shorter (P < 0.05). Ramsay scores were higher at 5 minutes, 15 minutes, and upon room exit (P < 0.05). Low-dose group and high-dose group had higher incidences of hallucination, lethargy, and diplopia within 2 hours (P < 0.05), and with low-dose group had lower incidences of hallucination, lethargy, and diplopia than high-dose group (P < 0.05).

CONCLUSION

Esketamine enhances analgesia and postpartum recovery; a 0.15 mg/kg dose is optimal for cesarean sections, balancing efficacy with minimized adverse effects.

A combined treatment for self-traumatic chronic skin lesions associated with post-surgical neuropathic pain in a domestic cat: a pharmacological and cold atmospheric plasma approach

Cold atmospheric plasma (CAP) has been employed as a therapy against both acute and chronic skin lesions, contaminated or not, and has effects on angiogenesis and reepithelialization promoting healing. In this context, the present study aimed to evaluate the effects of a CAP jet associated with pharmacological treatment described by the 2015 AAHA/AAFP pain management guidelines and the 2022 WSAVA guidelines for the recognition, assessment, and treatment of pain, on the healing of chronic skin lesions caused by a pruritic reaction resulting from post-surgical neuropathic pain. To this end, a single CAP application was performed on a feline patient with a 6 months old recurrent contaminated cervical skin lesions along with administration of ketamine (10 µg/kg/min) following the prescription of prednisone (1 mg/kg, SID, 6 days), gabapentin (8 mg/kg, BID, 60 days) and amitriptyline (0.5 mg /kg, SID, 60 days). A single application of plasma associated with an NMDA antagonist, anti-inflammatory steroid, tricyclic antidepressant and gabapentinoid thus provided a significant improvement in the macroscopic appearance of the lesion within 10 days, and the owner reported the cessation of intense itching within the first four hours after treatment and a consequent improvement in the animal's quality of life. The medical treatment was finished almost a year since the writing of this paper, without clinical or reported recurrent signs of the condition. Therefore, we observed that single dose CAP application associated with ketamine, gabapentin, amitriptyline and prednisone leads to significant healing of chronically infected skin lesions resulting from post-surgical neuropathic pain.

Potential Plausible Role of Stem Cell for Treating Depressive Disorder: a Retrospective Review

Depression poses a significant threat to global physical and mental health, impacting around 3.8% of the population with a rising incidence. Current treatment options primarily involve medication and psychological support, yet their effectiveness remains limited, contributing to high relapse rates. There is an urgent need for innovative and more efficacious treatment modalities. Stem cell therapy, a promising avenue in regenerative medicine for a spectrum of neurodegenerative conditions, has recently garnered attention for its potential application in depression. While much of this work remains preclinical, it has demonstrated considerable promise. Identified mechanisms underlying the antidepressant effects of stem cell therapy encompass the stimulation of neurotrophic factors, immune function modulation, and augmented monoamine levels. Nonetheless, these pathways and other undiscovered mechanisms necessitate further investigation. Depression fundamentally manifests as a neurodegenerative disorder. Given stem cell therapy's success in addressing a range of neurodegenerative pathologies, it opens the door to explore its application in depression treatment. This exploration may include repairing damaged nerves directly or indirectly and inhibiting neurotoxicity. Nevertheless, significant challenges must be overcome before stem cell therapies can be applied clinically. Successful resolution of these issues will ultimately determine the feasibility of incorporating stem cell therapies into the clinical landscape. This narrative review provides insights into the progress of research, potential avenues for exploration, and the prevailing challenges in the implementation of stem cell therapy for treatment of depression.

Neuropathic pain in cats: Mechanisms and multimodal management

PRACTICAL RELEVANCE

Chronic pain is a significant welfare concern in cats, and neuropathic pain, which arises from aberrant processing of sensory signals within the nervous system, is a subcategory of this type of pain. To comprehend this condition and how multimodal pharmacotherapy plays a central role in alleviating discomfort, it is crucial to delve into the anatomy of nociception and pain perception. In addition, there is an intricate interplay between emotional health and chronic pain in cats, and understanding and addressing the emotional factors that contribute to pain perception, and vice versa, is essential for comprehensive care.Clinical approach:Neuropathic pain is suspected if there is abnormal sensation in the area of the distribution of pain, together with a positive response to trial treatment with drugs effective for neuropathic pain. Ideally, this clinical suspicion would be supported by confirmation of a lesion at this neurolocalisation using diagnostic modalities such as MRI and neuroelectrophysiology. Alternatively, there may be a history of known trauma at that site. A variety of therapies, including analgesic, anti-inflammatory and adjuvant drugs, and neuromodulation (eg, TENS or acupuncture), can be employed to address different facets of pain pathways.Aim:This review article, aimed at primary care/ general practitioners, focuses on the identification and management of neuropathic pain in cats. Three case vignettes are included and a structured treatment algorithm is presented to guide veterinarians in tailoring interventions.Evidence base:The review draws on current literature, where available, along with the author's extensive experience and research.

Sida cordifolia L. attenuates behavioral hypersensitivity by interfering with KIF17-NR2B signaling in rat model of neuropathic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Sida cordifolia L., a perennial subshrub belonging to the Malvaceae family, holds noteworthy significance in the Indian Ayurvedic System and global texts. Roots of this plant are reported to be useful in neurodegenerative disorders, facial paralysis, and treating several neuropathic pain conditions such as neuralgia, and sciatica. However, despite these claims, there remains a dearth of experimental evidence showcasing the effectiveness of Sida cordifolia L. roots in mitigating neuropathic pain.

AIM OF THE STUDY

The primary objective of this study was to assess the analgesic properties of the whole extract (SCE) obtained from the roots of Sida cordifolia L., as well as its aqueous fraction (SAF) in rat model of chronic constriction injury (CCI)-induced neuropathic pain. Furthermore, in-depth phytochemical and molecular biology studies were conducted to identify the potential phytoconstituents and unveil the underlying mechanisms of action.

MATERIAL AND METHODS

DCM: Methanol (1:1) was used to extract the roots of Sida cordifolia L. to get whole extract (SCE) and was subjected to phytochemical investigations including LC-MS analysis. Analgesic potential of SCE was evaluated in chronic constriction injury (CCI) model of neuropathic pain in rats followed by its bioactivity guided fractionation using in-vitro anti-inflammatory assay and assessment of most potent fraction (SAF) in in-vivo pain model. We have also performed the detailed phytochemical and molecular biology investigations to delineate the mechanism of action of Sida cordifolia root extract.

RESULTS

Chronic constriction injury leads to significant decrease in paw withdrawal threshold and paw withdrawal latency indicating development of hypersensitivity in rodents. Treatment with SCE and its most potent aqueous fraction (SAF) leads to significant and dose-dependent reduction in pain-like behavior of nerve injured rats. Pro-inflammatory cytokines (TNF-α, IL-1β), glia cell markers (Iba1, ICAM1), neuropeptides (CGRP and Substance P), KIF-17 and NR2B expressions were found to be significantly upregulated in DRG and spinal cord of nerve injured rats. Treatment with SCE and SAF suppressed oxido-inflammatory cascade along with attenuation of KIF-17 mediated NR2B trafficking and neuroinflammation in DRG and spinal tissues of neuropathic rats. HPTLC and HR-MS analysis suggest betaine as major constituent in SAF which along with other phytoconstituents.

CONCLUSIONS

Both the whole extract (SCE) and the aqueous fraction (SAF) demonstrate a significant reduction in mechanical and thermal hypersensitivity by inhibiting KIF-17 mediated NR2B signaling in nerve injured rats and may be used as a potential alternative for the treatment of chronic pain. Our findings support the use of roots of Sida cordifolia L. in neuropathic pain conditions as acclaimed by its traditional use.

Stem cells and pain

Pain can be defined as an unpleasant sensory and emotional experience caused by either actual or potential tissue damage or even resemble that unpleasant experience. For years, science has sought to find treatment alternatives, with minimal side effects, to relieve pain. However, the currently available pharmacological options on the market show significant adverse events. Therefore, the search for a safer and highly efficient analgesic treatment has become a priority. Stem cells (SCs) are non-specialized cells with a high capacity for replication, self-renewal, and a wide range of differentiation possibilities. In this review, we provide evidence that the immune and neuromodulatory properties of SCs can be a valuable tool in the search for ideal treatment strategies for different types of pain. With the advantage of multiple administration routes and dosages, therapies based on SCs for pain relief have demonstrated meaningful results with few downsides. Nonetheless, there are still more questions than answers when it comes to the mechanisms and pathways of pain targeted by SCs. Thus, this is an evolving field that merits further investigation towards the development of SC-based analgesic therapies, and this review will approach all of these aspects.

Comparison of S-ketamine and midazolam for intravenous preoperative sedative and anxiolytic effects in preschool children: study protocol for a randomized controlled clinical trial

BACKGROUND

Preoperative anxiety management is gaining particular attention in paediatric anaesthesia. Pharmacological and non-pharmacological resorts can be implemented to address this special issue. Despite the various approaches currently used for preoperative sedation in children, the different sedative and anti-anxiety effects between the newly marketed anaesthetic, S-ketamine, and the traditional sedative, midazolam, are still unclear.

METHODS

This is a patient- and assessor-blinded randomized controlled clinical trial. Participants (n = 110) will receive S-ketamine (0.5 mg/kg) or midazolam (0.08 mg/kg) intravenously administrated at a ratio of 1:1 in the anaesthesia holding area. The primary outcome of this study is the sedative effect evaluated via the change in the modified Yale preoperative anxiety scale. It will be performed at two timepoints: in the pre-anaesthetic holding area before premedication (baseline, marked as T0) and about 5 min after premedication in the operating room without the existence of their guardians (marked as T1). Our secondary objectives include the parent separation anxiety score, postoperative agitation, caregivers' and anaesthesia care providers' satisfaction, and mask compliance.

DISCUSSION

This randomized controlled trial is the first study to compare the anti-anxiety effect of intravenous S-ketamine and midazolam. We will provide a new approach for the clinical management of preoperative anxiety in preschool children posted for elective surgery.

TRIAL REGISTRATION

ChiCTR2300069998. Registered on 30 March 2023.

GluN2A and GluN2B N-Methyl-D-Aspartate Receptor (NMDARs) Subunits: Their Roles and Therapeutic Antagonists in Neurological Diseases

N-methyl-D-aspartate receptors (NMDARs) are ion channels that respond to the neurotransmitter glutamate, playing a crucial role in the permeability of calcium ions and excitatory neurotransmission in the central nervous system (CNS). Composed of various subunits, NMDARs are predominantly formed by two obligatory GluN1 subunits (with eight splice variants) along with regulatory subunits GluN2 (GluN2A-2D) and GluN3 (GluN3A-B). They are widely distributed throughout the CNS and are involved in essential functions such as synaptic transmission, learning, memory, plasticity, and excitotoxicity. The presence of GluN2A and GluN2B subunits is particularly important for cognitive processes and has been strongly implicated in neurodegenerative diseases like Parkinson's disease and Alzheimer's disease. Understanding the roles of GluN2A and GluN2B NMDARs in neuropathologies provides valuable insights into the underlying causes and complexities of major nervous system disorders. This knowledge is vital for the development of selective antagonists targeting GluN2A and GluN2B subunits using pharmacological and molecular methods. Such antagonists represent a promising class of NMDA receptor inhibitors that have the potential to be developed into neuroprotective drugs with optimal therapeutic profiles.

Pharmacology of viable mechanism agnostic respiratory stimulants for the reversal of drug-induced respiratory depression in humans

INTRODUCTION

Drug-induced respiratory depression is potentially fatal and can be caused by various drugs such as synthetic opioids and tranquilizers. The only class of respiratory depressants that has a specific reversal agent are opioids, such as naloxone. These reversal agents have limited utility in situations of polysubstance ingestion with agents from multiple respiratory depressant classes. Hence, there is an unmet need for drugs that stimulate breathing irrespective of the underlying cause of respiratory depression, i.e. mechanism agnostic respiratory stimulants.

AREAS COVERED

In this review, we discuss agnostic respiratory stimulants, tested in humans with promising results, i.e. ampakines, drugs that act at the carotid bodies, N-methyl-D-aspartate receptor antagonist ketamine, and orexin receptor-2-agonist danavorexton, and others that demonstrated positive effects in animals but not yet in humans.

EXPERT OPINION

Rapid, effective rescuing of individuals who overdosed on respiratory depressants saves lives. While naloxone is the preferred drug for reversing opioid-induced respiratory depression, its effectiveness is limited in cases involving non-opioids. While several agnostic respiratory stimulants showed promise in humans, further research is needed to optimize dosing, evaluate safety and efficacy in deeper respiratory depression (apnea). Additionally, future studies should combine agnostic stimulants with naloxone, to improve rapid, effective rescue from drug overdoses.

Novel Drug Targets and Emerging Pharmacotherapies in Neuropathic Pain

Neuropathic pain is a debilitating condition characterized by abnormal signaling within the nervous system, resulting in persistent and often intense sensations of pain. It can arise from various causes, including traumatic nerve injury, neuropathy, and certain diseases. We present an overview of current and emerging pharmacotherapies for neuropathic pain, focusing on novel drug targets and potential therapeutic agents. Current pharmacotherapies, including tricyclic antidepressants, gabapentinoids, and serotonin norepinephrine re-uptake inhibitors, are discussed, as are emerging treatments, such as ambroxol, cannabidiol, and N-acetyl-L-cysteine. Additionally, the article highlights the need for further research in this field to identify new targets and develop more effective and targeted therapies for neuropathic pain management.

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.

Molecular mechanisms underlying the N-methyl-d-aspartate receptor antagonists: Highlighting their potential for transdiagnostic therapeutics

The so-called "psychedelic renaissance" has stimulated expanded interest in several classes of drugs that appear to possess transdiagnostic effects in the treatment of mental health disorders, specifically. N-methyl-d-aspartate receptor (NMDAR) antagonists are one such class with diverse therapeutic potential. NMDARs mediate excitatory postsynaptic signalling in the central nervous system (CNS) and are integral to normal neurobiological processes including neuronal development, synaptic transmission, and plasticity, and thus involved in learning and memory. However, NMDAR hyper-function is also implicated in acute CNS trauma, neuropsychiatric and neurodegenerative disorders, as well as chronic pain. The complex structure of NMDARs permits several locations for therapeutic inhibition, making these receptors a potential target for multiple drugs which modulate them in different ways. NMDAR antagonists, which may be competitive, non-competitive, or uncompetitive, either block glutamate from binding the receptor or modulate the response to glutamate binding. Despite longstanding concerns about side effects of NMDAR antagonists, recent research suggests that, when appropriately used, these agents have favourable safety profiles. Furthermore, their fast-acting mechanism of action, resulting in rapid effects compared to other therapeutic agents, makes them a promising class of drugs that may yield effective therapeutics for multiple CNS disorders.

NMDARs mediate peripheral and central sensitization contributing to chronic orofacial pain

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

S-Ketamine oral thin film—Part 2: Population pharmacodynamics of S-ketamine, S-norketamine and S-hydroxynorketamine

Ketamine is a versatile drug used for many indications and is administered via various routes. Here, we report on the pharmacodynamics of sublingual and buccal fast-dissolving oral-thin-films that contain 50 mg of S-ketamine in a population of healthy male and female volunteers. Twenty volunteers received one or two 50 mg S-ketamine oral thin films in a crossover design, placed for 10 min sublingually (n = 15) or buccally (n = 5). The following measurements were made for 6 h following the film placement: antinociception using three distinct pain assay; electrical, pressure, and heat pain, and drug high on an 11-point visual analog scale. Blood samples were obtained for the measurement of plasma S-ketamine, S-norketamine, and S-hydroxynorketamine concentrations. A population pharmacodynamic analysis was performed in NONMEM to construct a pharmacodynamic model of S-ketamine and its metabolites. P-values < 0.01 were considered significant. The sublingual and buccal 50 and 100 mg S-ketamine oral thin films were antinociceptive and produced drug high with effects lasting 2–6 h, although a clear dose-response relationship for antinociception could not be established. The effects were solely related to the parent compound with no contribution from S-norketamine or S-hydroxynorketamine. S-ketamine potency was lower for antinociception (C₅₀ ranging from 1.2 to 1.7 nmol/mL) than for drug high (C₅₀ 0.3 nmol/ml). The onset/offset of effect as defined by the blood-effect-site equilibration half-life did not differ among endpoints and ranged from 0 to 5 min. In conclusion, the 50-mg S-ketamine oral thin film was safe and produced long-term antinociception in all three nociceptive assays with side effects inherent to the use of ketamine. The study was registered at the trial register of the Dutch Cochrane Center (www.trialregister.nl) under identifier NL9267 and the European Union Drug Regulating Authorities Clinical Trials (EudraCT) database under number 2020-005185-33.

A Study on the Preventive Effect of Esketamine on Postpartum Depression (PPD) after Cesarean Section

Objective

The purpose of this study is to explore and analyze the preventive effect of esketamine on postpartum depression (PPD) after cesarean section.

Methods

A total of 138 puerperae who underwent cesarean section in our hospital from February 2020 to January 2022 were selected as the research subjects. The control group was given intravenous injection of 2 ml of normal saline after the fetus was delivered. Meanwhile, the observation group was given intravenous injection of a small dose of esketamine (esketamine 0.5 mg/kg+ 2 ml of normal saline) after the delivery of the fetus. The changes of blood pressure and heart rate, the Edinburgh Postnatal Depression Scale (EPDS) questionnaire scores and the incidence of postpartum depression were compared between the two groups. At the same time, the incidence of postoperative adverse events in the two groups was observed.

Results

There was no significant difference in systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) between the two groups at T1-T3 (P > 0.05). Compared with the control group, the SBP, DBP, and HR at T4 and T5 in the observation group were higher (P < 0.05). There was no significant difference in SBP, DBP, and HR at T3, T4, and T5 in the observation group (P > 0.05). Compared with T3, SBP, DBP, and HR were lower in control group T4 and T5, respectively. There was no significant difference in the EPDS scores between the two groups on the 1st day before delivery (P > 0.05). The EPDS scores of the two groups were higher at 3d postpartum and 42d postpartum, respectively, than at 1d before delivery. The EPDS scores of the observation group at 3d and 42d after delivery were lower than those in the control group (P < 0.05). Compared with the control group, the incidence of postpartum depression was higher in the observation group at 3 days postpartum and 1 month postpartum, respectively (P < 0.05). There was no significant difference in the incidence of postpartum adverse reactions between the two groups (P > 0.05).

Conclusion

The application of esketamine after cesarean section can effectively reduce depression-related scores and the risk of postpartum depression without increasing adverse reactions and has high safety.

S-Ketamine Oral Thin Film—Part 1: Population Pharmacokinetics of S-Ketamine, S-Norketamine and S-Hydroxynorketamine

Ketamine is administered predominantly via the intravenous route for the various indications, including anesthesia, pain relief and treatment of depression. Here we report on the pharmacokinetics of sublingual and buccal fast-dissolving oral-thin-films that contain 50 mg of S-ketamine in a population of healthy male and female volunteers. Twenty volunteers received one or two oral thin films on separate occasions in a randomized crossover design. The oral thin films were placed sublingually (n = 15) or buccally (n = 5) and left to dissolve for 10 min in the mouth during which the subjects were not allowed to swallow. For 6 subsequent hours, pharmacokinetic blood samples were obtained after which 20 mg S-ketamine was infused intravenously and blood sampling continued for another 2-hours. A population pharmacokinetic analysis was performed in NONMEM pharmacokinetic model of S-ketamine and its metabolites S-norketamine and S-hydroxynorketamine; p < 0.01 were considered significant. S-ketamine bioavailability was 26 ± 1% (estimate ± standard error of the estimate) with a 20% lower bioavailability of the 100 mg oral thin film relative to the 50 mg film, although this difference did not reach the level of significance. Due to the large first pass-effect, 80% of S-ketamine was metabolized into S-norketamine leading to high plasma levels of S-norketamine following the oral thin film application with 56% of S-ketamine finally metabolized into S-hydroxynorketamine. No differences in pharmacokinetics were observed for the sublingual and buccal administration routes. The S-ketamine oral thin film is a safe and practical alternative to intravenous S-ketamine administration that results in relatively high plasma levels of S-ketamine and its two metabolites.

Ketamine Psychedelic and Antinociceptive Effects Are Connected

BACKGROUND

Ketamine produces potent analgesia combined with psychedelic effects. It has been suggested that these two effects are associated and possibly that analgesia is generated by ketamine-induced dissociation. The authors performed a post hoc analysis of previously published data to quantify the pharmacodynamic properties of ketamine-induced antinociception and psychedelic symptoms. The hypothesis was that ketamine pharmacodynamics (i.e., concentration-effect relationship as well as effect onset and offset times) are not different for these two endpoints.

METHODS

Seventeen healthy male volunteers received escalating doses of S- and racemic ketamine on separate occasions. Before, during, and after ketamine infusion, changes in external perception were measured together with pain pressure threshold. A population pharmacokinetic-pharmacodynamic analysis was performed that took S- and R-ketamine and S- and R-norketamine plasma concentrations into account.

RESULTS

The pharmacodynamics of S-ketamine did not differ for antinociception and external perception with potency parameter (median [95% CI]) C50, 0.51 (0.38 to 0.66) nmol/ml; blood-effect site equilibration half-life, 8.3 [5.1 to 13.0] min), irrespective of administration form (racemic ketamine or S-ketamine). R-ketamine did not contribute to either endpoint. For both endpoints, S-norketamine had a small antagonistic effect.

CONCLUSIONS

The authors conclude that their data support an association or connectivity between ketamine analgesia and dissociation. Given the intricacies of the study related to the pain model, measurement of dissociation, and complex modeling of the combination of ketamine and norketamine, it is the opinion of the authors that further studies are needed to detect functional connectivity between brain areas that produce the different ketamine effects.

EDITOR’S PERSPECTIVE

From a Symptom-Based to a Mechanism-Based Pharmacotherapeutic Treatment in Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is a debilitating painful condition of a distal extremity that can develop after tissue damage. CRPS is thought to be a multimechanism syndrome and ideally the most prominent mechanism(s) should be targeted by drugs in an individually tailored manner. This review gives an overview of the action and evidence of current and future pharmacotherapeutic options for CRPS. The available options are grouped in four categories by their therapeutic actions on the CRPS mechanisms, i.e. inflammation, central sensitisation, vasomotor disturbances and motor disturbances. More knowledge about the underlying mechanisms of CRPS helps to specifically target important CRPS mechanisms. In the future, objective biomarkers could potentially aid in selecting appropriate mechanism-based drugs in order to increase the effectiveness of CRPS treatment. Using this approach, current and future pharmacotherapeutic options for CRPS should be studied in multicentre trials to prove their efficacy. The ultimate goal is to shift the symptom-based selection of therapy into a mechanism-based selection of therapy in CRPS.

Systems Pharmacology Modeling Identifies a Novel Treatment Strategy for Bortezomib-Induced Neuropathic Pain

Chemotherapy-induced peripheral neurotoxicity is a common dose-limiting side effect of several cancer chemotherapeutic agents, and no effective therapies exist. Here we constructed a systems pharmacology model of intracellular signaling in peripheral neurons to identify novel drug targets for preventing peripheral neuropathy associated with proteasome inhibitors. Model predictions suggested the combinatorial inhibition of TNFα, NMDA receptors, and reactive oxygen species should prevent proteasome inhibitor-induced neuronal apoptosis. Dexanabinol, an inhibitor of all three targets, partially restored bortezomib-induced reduction of proximal action potential amplitude and distal nerve conduction velocity in vitro and prevented bortezomib-induced mechanical allodynia and thermal hyperalgesia in rats, including a partial recovery of intraepidermal nerve fiber density. Dexanabinol failed to restore bortezomib-induced decreases in electrophysiological endpoints in rats, and it did not compromise bortezomib anti-cancer effects in U266 multiple myeloma cells and a murine xenograft model. Owing to its favorable safety profile in humans and preclinical efficacy, dexanabinol might represent a treatment option for bortezomib-induced neuropathic pain.

Beating Pain with Psychedelics: Matter over Mind?

Basic pain research has shed light on key cellular and molecular mechanisms underlying nociceptive and phenomenological aspects of pain. Despite these advances, [[we still yearn for] the discovery of novel therapeutic strategies to address the unmet needs of about 70% of chronic neuropathic pain patients whose pain fails to respond to opioids as well as to other conventional analgesic agents. Importantly, a substantial body of clinical observations over the past decade cumulatively suggests that the psychedelic class of drugs may possess heuristic value for understanding and treating chronic pain conditions. The present review presents a theoretical framework for hitherto insufficiently understood neuroscience-based mechanisms of psychedelics' potential analgesic effects. To that end, searches of PubMed-indexed journals were performed using the following Medical Subject Headings' terms: pain, analgesia, inflammatory, brain connectivity, ketamine, psilocybin, functional imaging, and dendrites. Recursive sets of scientific and clinical evidence extracted from this literature review were summarized within the following key areas: (1) studies employing psychedelics for alleviation of physical and emotional pain; (2) potential neuro-restorative effects of psychedelics to remediate the impaired connectivity underlying the dissociation between pain-related conscious states/cognitions and the subcortical activity/function leading to the eventual chronicity through immediate and long-term effects on dentritic plasticity; (3) anti-neuroinflammatory and pro-immunomodulatory actions of psychedelics as the may pertain to the role of these factors in the pathogenesis of neuropathic pain; (4) safety, legal, and ethical consideration inherent in psychedelics' pharmacotherapy. In addition to direct beneficial effects in terms of reduction of pain and suffering, psychedelics' inclusion in the analgesic armamentarium will contribute to deeper and more sophisticated insights not only into pain syndromes but also into frequently comorbid psychiatric condition associated with emotional pain, e.g., depressive and anxiety disorders. Further inquiry is clearly warranted into the above areas that have potential to evolve into further elucidate the mechanisms of chronic pain and affective disorders, and lead to the development of innovative, safe, and more efficacious neurobiologically-based therapeutic approaches.

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.

Ready for a "breakthrough" with ketamine? A look at recent pharmacological insights!

PURPOSE OF REVIEW

To update pharmacological insights on ketamine integrating information from different disciplines for developing steps to "breakthrough" approaches in clinical challenges.

RECENT FINDINGS

Pharmacokinetic/pharmacodynamic (PK/PD) models have incorporated recirculation, ketamine metabolites, drug-drug interaction, and covariates such as age. Ketamine-induced relief from treatment-resistant depression has been explained by "disinhibition" of gamma-aminobutyric acid-ergic interneurons and synaptogenic mechanisms requiring neurotrophic signals. Neuroimaging/electroencephalographic investigations have shown an increase in gamma spectral power in healthy volunteers and patients with depression, but also opposite changes in functional network connectivity after subanesthetic ketamine. Volunteer data may not be transferable to clinical conditions. Altered states of consciousness induced by subanesthetic ketamine have been described by disruption of resisting-state functional networks and frontoparietal connectivity with preservation of multisensory and sensor-motor networks. This has been interpreted as a "disconnected consciousness".

SUMMARY

More precise PK/PD models may improve the ketamine use regimen. The findings from research on depression are an important discovery because ketamine's impact on neuronal plasticity and synaptogenesis in human brain disease has directly been documented. Psychic adverse effects with subanesthetic ketamine are related to a "disconnected consciousness". Overall, progress has been made, but the "breakthrough" still has to come.

Pharmacokinetic Modeling of Ketamine Enantiomers and Their Metabolites After Administration of Prolonged-Release Ketamine With Emphasis on 2,6-Hydroxynorketamines

Modeling of metabolite kinetics after oral administration of ketamine is of special interest because of the higher concentrations of active metabolites because of the hepatic first-pass effect. This holds especially in view of the potential analgesic and antidepressant effects of 2R,6R- and 2S,6S-hydroxynorketamine at low doses of ketamine. Therefore, a 9-compartment model was developed to analyze the pharmacokinetics of ketamine enantiomers and their metabolites after racemic ketamine administered intravenously (5 mg) and as 4 doses (10, 20, 40, and 80 mg) of a prolonged-release formulation (PR-ketamine). Using a population approach, the serum concentration-time data of the enantiomers of ketamine, norketamine, dehydronorketamine, and 2,6-hydroxynorketamine obtained in 15 healthy volunteers could be adequately fitted. The estimated model parameters were used to simulate serum concentration-time profiles; after multiple dosing of PR-ketamine (2 daily doses of 20 mg), the steady-state concentrations of R- and S-ketamine were 1.4 and 1.3 ng/mL, respectively. The steady-state concentration of 2R,6R-hydroxynorketamine exceeded those of R-norketamine (4-fold), R-dehydonorketamine (8-fold), and R-ketamine (46-fold), whereas that of 2S,6S-hydroxynorketamine exceeded that of S-ketamine by 14-fold. The model may be useful for identifying dosing regimens aiming at optimal plasma concentrations of 2,6-hydroxynorketamines.

Chiral Pharmacokinetics and Metabolite Profile of Prolonged-release Ketamine Tablets in Healthy Human Subjects

BACKGROUND

The anesthetic ketamine after intravenous dosing is nearly completely metabolized to R- and S-stereoisomers of the active norketamine (analgesic, psychoactive) and 2,6-hydroxynorketamine (potential analgesic, antidepressant) as well as the inactive dehydronorketamine. Oral administration favors the formation of 2,6-hydroxynorketamines via extensive presystemic metabolism. The authors hypothesized that plasma exposure to 2,6-hydroxynorketamines relative to the psychoactive ketamine is greater after prolonged-release ketamine tablets than it is after intravenous ketamine.

METHODS

Pharmacokinetics of ketamine after intravenous infusion (5.0 mg) and single-dose administrations of 10, 20, 40, and 80 mg prolonged-released tablets were evaluated in 15 healthy white human subjects by means of a controlled, ascending-dose study. The stereoisomers of ketamine and metabolites were quantified in serum and urine by validated tandem mass-spectrometric assays and evaluated by noncompartmental pharmacokinetic analysis.

RESULTS

After 40 mg prolonged-release tablets, the mean ± SD area under the concentrations-time curve ratios for 2,6-hydroxynorketamine/ketamine were 18 ± 11 (S-stereoisomers) and 30 ± 16 (R-stereoisomers) compared to 1.7 ± 0.8 and 3.1 ± 1.4 and after intravenous infusion (both P < 0.001). After 10 and 20 mg tablets, the R-ratios were even greater. The distribution volumes at steady state of S- and R-ketamine were 6.6 ± 2.2 and 5.6 ± 2.1 l/kg, terminal half-lives 5.2 ± 3.4 and 6.1 ± 3.1 h, and metabolic clearances 1,620 ± 380 and 1,530 ± 380 ml/min, respectively. Bioavailability of the 40 mg tablets was 15 ± 8 (S-isomer) and 19 ± 10% (R-isomer) and terminal half-life 11 ± 4 and 10 ± 4 h. About 7% of the dose was renally excreted as S-stereoisomers and 17% as R-stereoisomers.

CONCLUSIONS

Prolonged-release ketamine tablets generate a high systemic exposure to 2,6-hydroxynorketamines and might therefore be an efficient and safer pharmaceutical dosage form for treatment of patients with chronic neuropathic pain compared to intravenous infusion.

EDITOR’S PERSPECTIVE

Stem Cell Therapy for Modulating Neuroinflammation in Neuropathic Pain

Neuropathic pain (NP) is a complex, debilitating, chronic pain state, heterogeneous in nature and caused by a lesion or disease affecting the somatosensory system. Its pathogenesis involves a wide range of molecular pathways. NP treatment is extremely challenging, due to its complex underlying disease mechanisms. Current pharmacological and nonpharmacological approaches can provide long-lasting pain relief to a limited percentage of patients and lack safe and effective treatment options. Therefore, scientists are focusing on the introduction of novel treatment approaches, such as stem cell therapy. A growing number of reports have highlighted the potential of stem cells for treating NP. In this review, we briefly introduce NP, current pharmacological and nonpharmacological treatments, and preclinical studies of stem cells to treat NP. In addition, we summarize stem cell mechanisms—including neuromodulation in treating NP. Literature searches were conducted using PubMed to provide an overview of the neuroprotective effects of stem cells with particular emphasis on recent translational research regarding stem cell-based treatment of NP, highlighting its potential as a novel therapeutic approach.

The multiple faces of ketamine in anaesthesia and analgesia

Objective

Ketamine is an anaesthetic agent with a unique dissociative profile and pharmacological effects ranging from the induction and maintenance of anaesthesia to analgesia and sedation, depending on the dose. This article provides information for the clinical use of ketamine in anaesthesia, in both conventional and special circumstances.

Methods

This is a non-systematic review of the literature, through a PubMed search up to February 2021.

Results

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations. It is suitable for patients with many heart conditions and, unlike other anaesthetics, its potential for cardiorespiratory depression is low. Furthermore, it may be used when venous access is difficult as it may be administered through various routes. Ketamine is the anaesthetic of choice for patients with bronchospasm thanks to its bronchodilatory and anti-inflammatory properties.

Conclusion

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations and is suitable for patients with many cardiac and respiratory conditions.

Stability of 10-mg/mL and 50-mg/mL ketamine oral solutions

PURPOSE

Ketamine is an anesthetic agent commonly used for the induction of anesthesia. Ketamine is also given to control pain, for treatment of posttraumatic stress disorder, and to induce bronchodilation in refractory asthma. Moreover, ketamine therapy is gaining ground as an intervention for patients with treatment-resistant depression and individuals who have depression with serious suicidal ideation. Recently, the drug has been used to disrupt maladaptive reward memories in individuals with harmful alcohol consumption behaviors. The stability of 10-mg/mL and 50-mg/mL ketamine solutions stored at ambient and refrigeration temperatures was assessed over 90 days.

METHODS

Three batches of 10-mg/mL and 50-mg/mL ketamine solutions were stored for 90 days under two temperature conditions (2°C-8°C and 22°C-25°C) in amber plastic bottles. Chemical stability was assessed using a stability-indicating high-performance liquid chromatography assay. At each study time, visual inspection and pH assessments of ketamine concentration and pH were conducted.

RESULTS

For all solutions tested at each condition, the ketamine concentration remaining was at least 98% of the initial concentration over 90 days of storage. Throughout the study period, solution pH remained stable and the color and odor of the suspensions remained unchanged.

CONCLUSION

Extemporaneously compounded 10-mg/mL and 50-mg/mL oral solutions of ketamine prepared in a flavored suspending excipient and stored in amber polypropylene plastic bottles were stable for at least 90 days at both ambient and refrigeration temperatures.

Cortical spreading depolarization and ketamine: a short systematic review

INTRODUCTION

Cortical spreading depolarization (SD) describes pathological waves characterized by an almost complete sustained depolarization of neurons and astrocytes that spreads throughout the cortex. In this study, we carried out a qualitative review of all available evidence, clinical and preclinical, on the use of ketamine in SD.

METHODS

We performed a systematic review of Medline, with no restrictions regarding publishing date or language, in search of articles reporting the use of ketamine in SD. The search string was composed of "ketamine," "spreading," "depolarization," and "depression" in both (AND) and (OR) combinations.

RESULTS

Twenty studies were included in the final synthesis. Many studies showed that ketamine effectively blocks SD in rats, swine, and humans. The first prospective randomized trial was published in 2018. Ten patients with severe traumatic brain injury or subarachnoid hemorrhage were enrolled, and ketamine showed a significant, dose-dependent effect on the reduction of SD.

CONCLUSION

The available evidence from preclinical studies is helping to translate the role of ketamine in blocking spreading depolarizations to clinical practice, in the settings of migraine with aura, traumatic brain injury, subarachnoid hemorrhage, and hemorrhagic and ischemic stroke. More randomized controlled trials are needed to determine whether interrupting the ketamine-blockable SDs effectively leads to an improvement in outcome and to assess the real occurrence of adverse effects.

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.

Stem Cells in the Treatment of Neuropathic Pain: Research Progress of Mechanism

Neuropathic pain (NP) is pain caused by somatosensory nervous system injury or disease. Its prominent symptoms are spontaneous pain, hyperalgesia, and allodynia, and the sense of pain is extremely strong. Owing to the complex mechanism, conventional painkillers lack effectiveness. Recently, research on the treatment of NP by stem cells is increasing and promising results have been achieved in preclinical research. In this review, we briefly introduce the neuropathic pain, the current treatment strategy, and the development of stem cell therapy, and we collected the experimental and clinical trial articles of many kinds of stem cells in the treatment of neuropathic pain from the past ten years. We analyzed and summarized the general efficacy and mechanism of stem cells in the treatment of neuropathic pain. We found that the multiple-mechanism approach was different from the single mechanism of routine clinical drugs; stem cells play a role in peripheral mechanism, central mechanism, and disinhibition of spinal cord level that lead to neuropathic pain, so they are more effective in analgesia and treatment of neuropathic pain.

Which idea is better with regard to immune response? Opioid anesthesia or opioid free anesthesia

The stress of surgery is characterized by an inflammatory response with immune suppression resulting from many factors, including the type of surgery and the kind of anesthesia, linked with the drugs that are used and the underlying disease of the patient. The trauma of surgery triggers a cascade of reactions involving the immune response and nociception. As strong analgesics, opioids provide the analgesic component of general anesthesia with bi-directional effect on the immune system. Opioids influence almost all aspects of the immune response in regards to leukocytes, macrophages, mast cells, lymphocytes, and NK cells. The suppressive effect of opioids on the immune system is limiting their use, especially in patients with impaired immune response, so the possibility of using multimodal anesthesia without opioids, known as opioid-free anesthesia (OFA), is gaining more and more sympathizers. The idea of OFA is to eliminate opioid analgesia in the treatment of acute pain and to replace it with drugs from other groups that are assumed to have a comparable analgesic effect without affecting the immune system. Here, we present a review on the impact of anesthesia, with and without the use of opioids, on the immune response to surgical stress.

Pharmacokinetics of ketamine and its major metabolites norketamine, hydroxynorketamine, and dehydronorketamine: a model-based analysis

BACKGROUND

Recent studies show activity of ketamine metabolites, such as hydroxynorketamine, in producing rapid relief of depression-related symptoms and analgesia. To improve our understanding of the pharmacokinetics of ketamine and metabolites norketamine, dehydronorketamine, and hydroxynorketamine, we developed a population pharmacokinetic model of ketamine and metabolites after i.v. administration of racemic ketamine and the S-isomer (esketamine). Pharmacokinetic data were derived from an RCT on the efficacy of sodium nitroprusside (SNP) in reducing the psychotomimetic side-effects of ketamine in human volunteers.

METHODS

Three increasing i.v. doses of esketamine and racemic ketamine were administered to 20 healthy volunteers, and arterial plasma samples were obtained for measurement of ketamine and metabolites. Subjects were randomised to receive esketamine/SNP, esketamine/placebo, racemic ketamine/SNP, and racemic ketamine/placebo on four separate occasions. The time-plasma concentration data of ketamine and metabolites were analysed using a population compartmental model approach.

RESULTS

The pharmacokinetics of ketamine and metabolites were adequately described by a seven-compartment model with two ketamine, norketamine, and hydroxynorketamine compartments and one dehydronorketamine compartment with metabolic compartments in-between ketamine and norketamine, and norketamine and dehydronorketamine main compartments. Significant differences were found between S- and R-ketamine enantiomer pharmacokinetics, with up to 50% lower clearances for the R-enantiomers, irrespective of formulation. Whilst SNP had a significant effect on ketamine clearances, simulations showed only minor effects of SNP on total ketamine pharmacokinetics.

CONCLUSIONS

The model is of adequate quality for use in future pharmacokinetic and pharmacodynamic studies into the efficacy and side-effects of ketamine and metabolites.

CLINICAL TRIAL REGISTRATION

Dutch Cochrane Center 5359.