Pharmacotherapy: Ketamine and Esketamine

Low (micro)doses of 2,5-dimethoxy-4-propylamphetamine (DOPR) increase effortful motivation in low-performing mice

Treating amotivated states remains difficult. Classical psychedelic drugs (5-HT2A receptor agonists) such as LSD and psilocybin have shown therapeutic potential in treating such symptoms, but their development has been hindered by their undesirable hallucinogenic effects. There is increasing evidence that administration of psychedelics at dose levels too low to evoke a hallucinogenic effect ("microdoses") may have therapeutic value in contexts of mood and cognition. 2,5-Dimethoxy-4-propylamphetamine (DOPR) is a psychedelic phenethylamine compound acting as a 5-HT2A receptor agonist. We used a combination of behavioral assays to determine the motivational and hallucinogenic-like effects of DOPR and identify the dose ranges at which each of these effects were observed. In mice, the motivational effects of psychedelic compounds were assessed using the progressive ratio breakpoint task (PRBT, n = 80), a translational assay sensitive to changes in motivation. Psychedelic-like effects were gauged using the mouse head-twitch response (HTR, n = 72) assay, a preclinical readout of psychedelic potential. Significant improvements in PRBT performance were seen at doses as low as 0.0106 mg/kg in animals with low baseline PRBT scores while high-performing PRBT mice were unaffected. DOPR only induced significant HTR at doses ≥0.1 mg/kg. Together, these results indicate that the psychedelic DOPR may increase motivation in those with a low motivated state. Importantly, these effects may be attainable at low doses below the threshold required to induce psychedelic subjective effects. Hence, the ability of low doses of DOPR and other psychedelic drugs to alleviate amotivated states in rodents manipulated to induce disease-relevant states should be investigated.

Chronic, combinatorial targeting of NMDARs and 5-HT4Rs exerts extended behavioral effects against stress-induced perseverative behavior and hyponeophagia

Serotonin (5-HT) receptors and N-methyl-D-aspartate receptors (NMDARs) have both been implicated in stress-induced psychiatric disorders. However, there is a paucity of studies evaluating the effectiveness of novel combinatorial pharmacological treatments to treat stress-related disorders. Here, we evaluated whether administration of combinatorial (R,S)-ketamine, an NMDAR antagonist and Food and Drug Administration (FDA)-approved anesthetic, and prucalopride, a 5-HT type IV receptor (5-HT4R) agonist and FDA-approved drug for chronic idiopathic constipation (CIC), would have additional effects when administered after stress. A single injection of saline (Sal), (R,S)-ketamine (K), prucalopride (P), or a combined dose of (R,S)-ketamine and prucalopride (K + P) was administered for 1x, 2x, or 7x per week for 2 weeks after either contextual fear conditioning (CFC), learned helplessness (LH), stress enhanced fear learning (SEFL), or chronic corticosterone (CORT) stress in both sexes. Drug efficacy was assayed using assays to measure fear, behavioral despair, perseverative, and/or hyponeophagia. Combinatorial drug administration was also tested using intranasal delivery. We found that combinatorial K + P exerted additional effects, compared to either drug alone, in reducing a variety of stress-induced behaviors in both sexes. Moreover, intranasal dosing was also effective. Our results indicate that chronic administration of K + P has extended benefits for combating stress-induced pathophysiology. Our findings provide strong evidence that future clinical studies using this chronic treatment strategy may prove advantageous in decreasing a broad range of stress-induced psychiatric disorders.

The Assessment of the Safety Profile of Selective Serotonin Reuptake Inhibitors Versus Other Antidepressants: Drug-Drug Interaction Insights from EudraVigilance

Depression persists as one of the illnesses described relentlessly through the centuries because it affects a large group of people. Background/Objectives: The treatment of depression consists of various therapeutic agents, among which selective serotonin reuptake inhibitors (SSRIs) are elective. As polypharmacy tends to become the norm in modern days, the study of the real-life occurrence of drug-drug interactions is imperative. The aim of this study was the evaluation of drug-drug interactions (DDIs) between antidepressant medicines, namely SSRIs (each representative) versus eleven representatives from other antidepressant classes. Methods: Based on the spontaneous safety reports (ICSRs) uploaded to EudraVigilance until the end of July 2024, the descriptive and the disproportionality analyses were performed, and results were interpreted in the context of pharmacologic variability. Results: SSRIs were the focus of 137,369 ICSRs while for the other antidepressants, namely amitriptyline, clomipramine, duloxetine, venlafaxine, mirtazapine, bupropion, trazodone, tianeptine, agomelatine, brexpiprazole, and esketamine, a total of 155,458 reports were registered. The most notable differences appeared in psychiatric adverse drug reactions. Except fluvoxamine (n = 463), the remaining SSRIs had a higher number of DDIs reported (n = 1049 for escitalopram and n = 1549 for sertraline) compared to other antidepressants. However, similar numbers of DDIs were reported for duloxetine (n = 1252) and venlafaxine (n = 1513). Sertraline unspecified DDIs were reported with a higher probability compared to all other drugs (e.g., esketamine ROR: 9.37, 95% CI: 5.17-16.96, tianeptine ROR: 4.08, 95% CI: 2.49-6.69, etc.). Conclusions: SSRIs, although known to influence various cytochrome P450 isoenzymes, have not shown higher inhibitory interactions compared to any of the drugs selected as reference. Sertraline appears in more reports concerning DDIs than the other antidepressants. Still, further real world studies related to the DDIs of SSRIs are needed to complete the relevant knowledge level.

Towards an expanded neurocognitive account of ketamine's rapid antidepressant effects

Ketamine is an N-methyl-D-aspartate receptor antagonist that has shown effectiveness as a rapidly acting treatment for depression. Although advances have been made in understanding ketamine's antidepressant pharmacological and molecular mechanisms of action, the large-scale neurocognitive mechanisms driving its therapeutic effects are less clearly understood. To help provide such a framework, we provide a synthesis of current evidence linking ketamine treatment to the modulation of brain systems supporting reward processing, interoception, and self-related cognition. We suggest that ketamine's antidepressant effects are, at least in part, driven by dynamic multi-level influences across these key functional domains.

Effect of different modes of administration of esketamine combined with supraclavicular brachial plexus block on the incidence of rebound pain after upper limb fracture surgery: study protocol for a single-centre, double-blinded, randomised controlled trial

BACKGROUND

Supraclavicular brachial plexus block (SCB) is a common regional analgesic technique for upper limb fracture surgery, but it often leads to rebound pain. Our primary aim is to determine whether different administration methods of esketamine can reduce rebound pain in patients undergoing SCB for upper limb fracture surgery.

METHODS/DESIGN

This study is designed as a single-centre, double-blinded, prospective, randomised controlled trial. Patients undergoing upper limb fracture surgery, who plan to use a tourniquet, aged 18-60 years, with a body mass index of 18-30 kg/m2 and an American Society of Anaesthesiologists classification of I-III will be randomised into three groups after providing written informed consent: group N (perineural esketamine/ropivacaine); group V (intravenous esketamine/perineural ropivacaine); and group C (perineural ropivacaine). The primary outcome will be the percentage of patients experiencing rebound pain within 24 hours postoperatively. Secondary outcomes include the Numeric Rating Scale (NRS) score of rebound pain, the onset of rebound pain, (since performing SCB), the cumulative area under the curve of NRS pain severity scores through 48 hours postsurgery, postoperative opioid consumption at 48 hours postoperatively, onset and duration of the sensory blockade, onset and duration of the motor blockade and adverse reactions and adverse events. Patients will be followed-up to 48 hours postoperatively.

DISCUSSIONS

This protocol describes the design of a randomised controlled trial to evaluate the effect of different modes of administration of esketamine combined with SCB on the incidence of rebound pain after upper limb fracture surgery. The results may help to identify the most effective methods for managing pain in patients undergoing upper limb fracture surgery.

ETHICS AND DISSEMINATION

This study has been approved by the Ethics Committee of the Deyang People's Hospital (2023-03-010-K01). It was registered on the Chinese Clinical Trials Registry on 24 August 2023. We intend to publish the results in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ChiCTR2300075083.

Esketamine administered epidurally as an adjuvant to epidural ropivacaine for labour analgesia: a prospective, double-blind dose-response study

OBJECTIVE

To investigate the efficacy of esketamine as an adjuvant to epidural ropivacaine for labour analgesia by determining its effect on the median effective concentration (EC50) in a 20 ml volume of ropivacaine.

DESIGN

A prospective, double-blind dose-response study.

SETTING

This study was conducted in Women's Hospital, School of Medicine, Zhejiang University, China.

PARTICIPANTS

One hundred and fifty parturients who requested epidural analgesia were recruited in this study to randomly receive epidural ropivacaine alone or with esketamine of 0.2 mg ml-1, 0.3 mg ml-1, 0.4 mg ml-1 or 0.5 mg ml-1, respectively.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome, EC50 of ropivacaine, was determined using an up-down sequential allocation technique. The secondary outcomes were analgesia characteristics, Ramsay Sedation Scale score, labour duration, caesarean section rate and adverse effects.

RESULTS

The EC50 of ropivacaine with the addition of esketamine at concentrations of 0.3 mg ml-1, 0.4 mg ml-1 and 0.5 mg ml-1 resulted in significant reductions in the EC50 of ropivacaine to 0.050%, 0.044% and 0.043%, respectively, from baseline (esketamine 0 mg ml-1) (p<0.0001). However, reductions of the EC50 of ropivacaine were similar among the groups with esketamine of 0.3 mg ml-1, 0.4 mg ml-1 and 0.5 mg ml-1 (p>0.05). The Ramsay Sedation Scale score was higher and more dizziness was observed in the Group of esketamine 0.5 mg ml-1 compared with all other groups (p<0.0001). During the peripartum period, no differences in sensory blockade level, Bromage score, labour duration and percentage of caesarean delivery were found among the groups.

CONCLUSIONS

Under the conditions of this study, the addition of epidural esketamine of 0.3 mg⋅mL-1, 0.4 mg⋅mL-1 and 0.5 mg⋅mL-1 offered a similar ropivacaine dose-sparing effect; 0.5 mg⋅mL-1 of esketamine produced more adverse effects.

TRIAL REGISTRATION NUMBER

ChiCTR2100054348.

Ketamine, Esketamine, and Arketamine: Their Mechanisms of Action and Applications in the Treatment of Depression and Alleviation of Depressive Symptoms

Research over the past years has compared the enantiomers (S)-ketamine (esketamine) and (R)-ketamine (arketamine) of the previously known racemic mixture called ketamine (R/S-ketamine). Esketamine has been found to be more potent, offering three times stronger analgesic effects and 1.5 times greater anesthetic efficacy than arketamine. It provides smoother anesthesia with fewer side effects and is widely used in clinical settings due to its neuroprotective, bronchodilatory, and antiepileptic properties. Approved by the FDA and EMA in 2019, esketamine is currently used alongside SSRIs or SNRIs for treatment-resistant depression (TRD). On the other hand, arketamine has shown potential for treating neurological disorders such as Alzheimer's, Parkinson's, and multiple sclerosis, offering possible antidepressant effects and anti-inflammatory benefits. While esketamine is already in clinical use, arketamine's future depends on further research to address its safety, efficacy, and optimal dosing. Both enantiomers hold significant clinical value, with esketamine excelling in anesthesia, and arketamine showing promise in neurological and psychiatric treatments.

Ketamine alleviates PTSD-like effect and improves hippocampal synaptic plasticity via regulation of GSK-3β/GR signaling of rats

BACKGROUND

Each year, 3-4% of the global population experiences post-traumatic stress disorder (PTSD), a chronic mental disorder with significant social and economic repercussions. Although it has been shown that ketamine can effectively alleviate PTSD symptoms in individuals, the specific mechanism of action underlying its anti-PTSD effects remains unclear. In this study, we investigated how a single, low dose of ketamine affected the glycogen synthase kinase 3β (GSK-3β)/glucocorticoid receptor (GR) signaling pathway in a single prolonged stress (SPS)-induced PTSD rat model.

METHODS

After establishing the model, stress-related behavioral alterations in the rats were assessed following intraperitoneal injections of ketamine (10 mg/kg) and GSK-3β antagonist SB216763 (5 mg/kg). In the hippocampus, alterations in the expression of specific proteins implicated in PTSD development, such as GR, brain-derived neurotrophic factor (BDNF), GSK-3β, and phosphorylated glycogen synthase kinase 3β (p-GSK-3β), were assessed. We also measured changes in the mRNA expression levels of GR, BDNF, GSK-3β, FK501 binding protein 51 (FKBP5), and corticotropin-releasing hormone (CRH), as well as synaptic ultrastructure, in the hippocampus, and measured changes in corticosterone levels in the blood.

RESULTS

SPS induced anxiety-like and depression-like behaviors in rats and induced morphological changes in synapse, which were accompanied by higher GSK-3β protein expression and conversely, decreased expression of GR, BDNF, p-GSK-3β, FKBP5 and CRH. Intraperitoneal administration of ketamine (10 mg/kg) after SPS prevented SPS-induced anxiety-like behaviors. Most importantly, ketamine attenuated SPS-induced dysfunctions in GSK-3β/GR signaling and synaptic deficits. Furthermore, treatment with a GSK-3β inhibitor played the same effect as ketamine on behavioral changes of SPS model rats.

CONCLUSION

Single doses of ketamine effectively ameliorate SPS-induced anxiety-like symptoms, potentially by improving synaptic plastic in the hippocampus by regulating GSK-3β/GR signaling.

Esketamine Combined with Dexmedetomidine to reduce Visceral Pain During elective Cesarean Section Under Combined Spinal-Epidural Anesthesia: A double-Blind Randomized Controlled Study

Purpose

We aimed to evaluate the effect of intravenous esketamine combined with dexmedetomidine as supplemental analgesia in reducing intraoperative visceral pain during elective cesarean section under combined spinal-epidural anesthesia (CSEA).

Patients and Methods

A total of 269 parturients scheduled for elective cesarean section under CSEA between May 2023 and August 2023 were assessed. The parturients were randomly allocated to receiving either intravenous infusion of 0.3-mg/kg esketamine combined with 0.5-μg/kg dexmedetomidine (group ED, n=76), 0.5-μg/kg dexmedetomidine (group D, n=76), or normal saline (group C, n=76) after umbilical cord clamping. The primary outcome was intraoperative visceral pain. Secondary outcomes included the visual analog scale (VAS) score for pain evaluation and other intraoperative complications.

Results

The incidence of visceral pain was lower in group ED [9 (12.7%)] than in group D [32 (43.8%)] and group C [36 (48.6%), P <0.0001]. The VAS score was also lower in group ED when exploring abdominal cavity [0 (0), P <0.0001] and suturing the muscle layer [0 (0), P =0.036]. The mean arterial pressure was higher in group D [83 (9) mmHg] and group ED [81 (11) mmHg] than in group C [75 (10) mmHg, P <0.0001] after solution infusion. The heart rate after infusion of the solution was lower in group D [80 (12) bpm] than in group C [86 (14) bpm] and group ED [85 (12) bpm, P = 0.016]. The incidence of transient neurologic or mental symptoms was higher in group ED compared to group C and group D (76.1% vs 18.9% vs 23.3%, P<0.0001).

Conclusion

During cesarean section, 0.3-mg/kg esketamine combined with 0.5-μg/kg dexmedetomidine can alleviate visceral traction pain and provide stable hemodynamics. Parturients receiving this regimen may experience transient neurologic or mental symptoms that can spontaneously resolve at the end of the surgery.

The role and mechanism of esketamine in preventing and treating remifentanil-induced hyperalgesia based on the NMDA receptor-CaMKII pathway

Remifentanil-induced hyperalgesia (RIH) is a common clinical phenomenon that limits the use of opioids in pain management. Esketamine, a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has been shown to prevent and treat RIH. However, the underlying effect mechanism of esketamine on RIH remains unclear. This study aimed to investigate the role and mechanism of esketamine in preventing and treating RIH based on the NMDA receptor-CaMKIIα pathway. In this study, an experimental animal model was used to determine the therapeutic effect of esketamine on pain elimination. Moreover, the mRNA transcription and protein expression levels of CaMKII and GluN2B were investigated to offer evidence of the protective capability of esketamine in ameliorating RIH. The results demonstrated that esketamine attenuated RIH by inhibiting CaMKII phosphorylation and downstream signaling pathways mediated by the NMDA receptor. Furthermore, ketamine reversed the upregulation of spinal CaMKII induced by remifentanil. These findings suggest that the NMDA receptor-CaMKII pathway plays a critical role in the development of RIH, and ketamine's effect on this pathway may provide a new therapeutic approach for the prevention and treatment of RIH.

Efficacy, Safety, and Tolerability of Psychedelics in Treatment-Resistant Depression (TRD)

Major depressive disorder (MDD) is a highly prevalent psychiatric disorder, associated with substantial burden and large economical costs. Notwithstanding various conventional antidepressant treatment options, a large portion of depressed people (ca. 30%) fails to respond to first-line treatment, resulting in treatment-resistant depression (TRD). Although non-response to multiple antidepressant interventions is a common outcome, a consensus definition of TRD is not yet available. In practice, TRD is applied when two or more successive treatments with different antidepressants are not working. The last decade's intense research into new medicines for TRD has led to two developments, using typical or serotonergic (psilocybin, ayahuasca) and atypical (glutamatergic) psychedelics (ketamine, esketamine). Both approaches, although via different entrance mechanism, exhibit a fast onset but also long-lasting antidepressant effect far beyond the biological presence of the drug in the body, strongly indicating that downstream mechanisms activated by signaling cascades in the brain are involved. The present chapter describes the clinical development of psilocybin and esketamine for TRD and discusses the problems involved in the use of a proper placebo because of the psychotomimetic (psilocybin) or dissociative (ketamine) effects that interfere with performing "blind" studies. Nevertheless, intranasal esketamine was developed and approved for TRD, whereas psilocybin has shown positive results. Adverse effects and tolerability of both drugs in the dose ranges used are generally acceptable. The emergence of anti-TRD medicines for treatment of a very severe disease is a breakthrough in psychiatry.

Psychopharmacological Approaches for Neural Plasticity and Neurogenesis in Major Depressive Disorders

Major depressive disorder (MDD) is a mental health disorder associated with cognitive impairment, dysregulated appetite, fatigue, insomnia or hypersomnia, and severe mood changes that significantly impact the ability of the affected individual to perform day-to-day tasks, leading to suicide in the worst-case scenario. As MDD is becoming more prevalent, affecting roughly 300 million individuals worldwide, its treatment has become a major point of interest. Antidepressants acting as selective serotonin reuptake inhibitors (SSRIs) are currently used as the first line of treatment for MDD. Other antidepressants currently used for the treatment of MDD include the serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), and monoamine oxidase inhibitors (MAOIs). However, although effective in alleviating symptoms of MDD, most antidepressants require weeks or even months of regular administration prior to eliciting a rational clinical effect. Owing to the strong evidence showing a relationship between neural plasticity, neurogenesis, and MDD, researchers have also looked at the possibility of using treatment modalities that target these processes in an attempt to improve clinical outcome. The overarching aim of this chapter is to highlight the role of neural plasticity and neurogenesis in the pathophysiology of MDD and discuss the most recently studied treatment strategies that target these processes by presenting supporting evidence from both animal and human studies.