Long-term outcome of patients who receive ketamine during research

Interleaved Propofol-Ketamine Maintains DBS Physiology and Hemodynamic Stability: A Double-Blind Randomized Controlled Trial

BACKGROUND

The gold standard anesthesia for deep brain stimulation (DBS) surgery is the "awake" approach, using local anesthesia alone. Although it offers high-quality microelectrode recordings and therapeutic-window assessment, it potentially causes patients extreme stress and might result in suboptimal surgical outcomes. General anesthesia or deep sedation is an alternative, but may reduce physiological testing reliability and lead localization accuracy.

OBJECTIVES

The aim is to investigate a novel anesthesia regimen of ketamine-induced conscious sedation for the physiological testing phase of DBS surgery.

METHODS

Parkinson's patients undergoing subthalamic DBS surgery were randomly divided into experimental and control groups. During physiological testing, the groups received 0.25 mg/kg/h ketamine infusion and normal saline, respectively. Both groups had moderate propofol sedation before and after physiological testing. The primary outcome was recording quality. Secondary outcomes included hemodynamic stability, lead accuracy, motor and cognitive outcome, patient satisfaction, and adverse events.

RESULTS

Thirty patients, 15 from each group, were included. Intraoperatively, the electrophysiological signature and lead localization were similar under ketamine and saline. Tremor amplitude was slightly lower under ketamine. Postoperatively, patients in the ketamine group reported significantly higher satisfaction with anesthesia. The improvement in Unified Parkinson's disease rating scale part-III was similar between the groups. No negative effects of ketamine on hemodynamic stability or cognition were reported perioperatively.

CONCLUSIONS

Ketamine-induced conscious sedation provided high quality microelectrode recordings comparable with awake conditions. Additionally, it seems to allow superior patient satisfaction and hemodynamic stability, while maintaining similar post-operative outcomes. Therefore, it holds promise as a novel alternative anesthetic regimen for DBS. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Ketamine: A Practical Review for the Consultation-Liaison Psychiatrist

BACKGROUND

Ketamine is a noncompetitive N-methyl-D-aspartate-receptor antagonist often used for sedation and management of acute agitation in general hospital settings. Many hospitals now include ketamine as part of their standard agitation protocol, and consultation-liaison psychiatrists frequently find themselves treating patients who have received ketamine, despite lack of clear recommendations for management.

OBJECTIVE

Conduct a nonsystematic narrative review regarding the use of ketamine for agitation and continuous sedation, including benefits and adverse psychiatric effects. Compare ketamine to more traditional agents of agitation control. Provide consultation-liaison psychiatrists with a summary of available knowledge and recommendations for managing patients receiving ketamine.

METHODS

A literature review was performed using PubMed, querying published articles from inception to March 2023 for articles related to use of ketamine for agitation or continuous sedation and side effects including psychosis and catatonia.

RESULTS

A total of 37 articles were included. Ketamine was found to have multiple benefits, including shorter time to adequate sedation for agitated patients when compared to haloperidol ± benzodiazepines and unique advantages for continuous sedation. However, ketamine carries significant medical risks including high rates of intubation. Ketamine appears to induce a syndrome that mimics schizophrenia in healthy controls, and such effects are more pronounced and longer-lasting in patients with schizophrenia. Evidence regarding rates of delirium with ketamine for continuous sedation is mixed and requires further investigation before the agent is widely adopted for this purpose. Finally, the diagnosis of "excited delirium syndrome" and use of ketamine to treat this controversial syndrome warrants critical evaluation.

CONCLUSIONS

Ketamine carries many potential benefits and can be an appropriate medication for patients with profound undifferentiated agitation. However, intubation rates remain high, and ketamine may worsen underlying psychotic disorders. It is essential that consultation-liaison psychiatrists understand the advantages, disadvantages, biased administration, and areas of limited knowledge regarding ketamine.

Ketamine for psychotic depression: An overview of the glutamatergic system and ketamine's mechanisms associated with antidepressant and psychotomimetic effects

Approximately 0.35-1% of the general population is afflicted with psychotic depression at some time in their life. Psychotic depression is a subtype of major depressive disorder characterized by mood congruent hallucinations and/or delusions. Patients with psychotic depression often represent the most severe cases, with high relapse and mortality rate. Although treatment guidelines recommend a combination of antidepressants and antipsychotics or electroconvulsive therapy, most patients subsequently relapse due to treatment resistance. Furthermore, with the concern of antipsychotic drug's side effects (e.g., tardive dyskinesia), there is a need for an alternative pharmacotherapy for psychotic depression. Recently, several case studies demonstrated that treatment with ketamine not only ameliorated mood, but also improved psychotic symptoms in patients with treatment-resistant depression and psychotic features. However, the safety of ketamine in these patients is controversial since ketamine is known to induce psychotomimetic and dissociative effects. Additionally, the efficacy and safety of ketamine in patients with psychotic depression has not been established as most clinical trials have excluded these persons due to the theorized risk of aggravating psychotic symptoms. Notwithstanding, it is not established empirically that ketamine treatment in psychotic depression would predictably amplify psychotic symptoms and/or overall illness presentation. Future trials evaluating ketamine in depression should include patients with psychotic features to inform whether ketamine is safe and effective in this subpopulation.

The next psychoactive drugs: From imipramine to ketamine

Since the 1950s, the therapeutic arsenal against depression has grown considerably. From the discovery of mono-amine oxidase inhibitors (MAOIs) to the antidepressant effect of ketamine, several pharmacological breakthroughs made the history of psychiatry. These discoveries oriented the research about the pathophysiology of depression, which is one of the most disabling diseases worldwide affecting 10 to 20% of general population. In this article, we offer a short historical review of the various therapeutic options developed over the past century and the consequences of these innovations. We then review the discovery of the antidepressant effects of ketamine (and its S-enantiomer, esketamine), the lastest development in depression treatment. Ketamine's effects are spectacular both in terms of their very short onset time, and because they are observed even in treatment-resistant depression. Just as MAOIs and tricyclic antidepressants allowed the "monoaminergic hypothesis of depression" to emerge, unravelling the mechanisms of ketamine's antidepressant effects should highlight the role of glutamatergic system and neuro-inflammation in the neurobiology of depression. Ketamine might also help to refine our understanding of the cognitive pathophysiology of depression and to deeply transform the clinical representations of depressive disorder.

[The next psychoactive drugs: From imipramine to ketamine]

Depuis les années 1950, l’arsenal thérapeutique permettant de lutter contre la dépression s’est considérablement enrichi. De la découverte des inhibiteurs de la monoamine oxydase (IMAO) à celle de la kétamine, ces percées pharmacologiques ont marqué l’histoire de la psychiatrie et guidé la recherche sur la physiopathologie de la dépression, cette pathologie dévastatrice affectant entre 10 et 20 % de la population mondiale. Nous proposons dans cet article une courte revue historique des différentes options thérapeutiques développées au cours du siècle passé et des conséquences qu’ont eu ces innovations. Nous réalisons ensuite un état des lieux de la plus récente de ces découvertes, celle des effets antidépresseurs de la kétamine (et de son énantiomère S, l’eskétamine), spectaculaires de par leur délai d’apparition et leur efficacité même dans les formes les plus résistantes de dépression. De même que la découverte des IMAO et des tricycliques a permis de concevoir une théorie monoaminergique de la dépression, l’étude des mécanismes d’actions de la kétamine pourrait permettre de comprendre le rôle de la transmission glutamatergique ou de la neuro-inflammation dans la neurobiologie de cette pathologie, d’affiner nos connaissances sur sa physiopathologie cognitive ou encore de transformer en profondeur les représentations des cliniciens sur cette maladie.

Association of Ketamine With Psychiatric Symptoms and Implications for Its Therapeutic Use and for Understanding Schizophrenia: A Systematic Review and Meta-analysis

Importance

Ketamine hydrochloride is increasingly used to treat depression and other psychiatric disorders but can induce schizophrenia-like or psychotomimetic symptoms. Despite this risk, the consistency and magnitude of symptoms induced by ketamine or what factors are associated with these symptoms remain unknown.

Objective

To conduct a meta-analysis of the psychopathological outcomes associated with ketamine in healthy volunteers and patients with schizophrenia and the experimental factors associated with these outcomes.

Data Sources

MEDLINE, Embase, and PsychINFO databases were searched for within-participant, placebo-controlled studies reporting symptoms using the Brief Psychiatric Rating Scale (BPRS) or the Positive and Negative Syndrome Scale (PANSS) in response to an acute ketamine challenge in healthy participants or patients with schizophrenia.

Study Selection

Of 8464 citations retrieved, 36 studies involving healthy participants were included. Inclusion criteria were studies (1) including healthy participants; (2) reporting symptoms occurring in response to acute administration of subanesthetic doses of ketamine (racemic ketamine, s-ketamine, r-ketamine) intravenously; (3) containing a placebo condition with a within-subject, crossover design; (4) measuring total positive or negative symptoms using BPRS or PANSS; and (5) providing data allowing the estimation of the mean difference and deviation between the ketamine and placebo condition.

Data Extraction and Synthesis

Two independent investigators extracted study-level data for a random-effects meta-analysis. Total, positive, and negative BPRS and PANSS scores were extracted. Subgroup analyses were conducted examining the effects of blinding status, ketamine preparation, infusion method, and time between ketamine and placebo conditions. The Meta-analysis of Observational Studies in Epidemiology (MOOSE) and Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed.

Main Outcomes and Measures

Standardized mean differences (SMDs) were used as effect sizes for individual studies. Standardized mean differences between ketamine and placebo conditions were calculated for total, positive, and negative BPRS and PANSS scores.

Results

The overall sample included 725 healthy volunteers (mean [SD] age, 28.3 [3.6] years; 533 [73.6%] male) exposed to the ketamine and placebo conditions. Racemic ketamine or S-ketamine was associated with a statistically significant increase in transient psychopathology in healthy participants for total (SMD = 1.50 [95% CI, 1.23-1.77]; P < .001), positive (SMD = 1.55 [95% CI, 1.29-1.81]; P < .001), and negative (SMD = 1.16 [95% CI, 0.96-1.35]; P < .001) symptom ratings relative to the placebo condition. The effect size for this association was significantly greater for positive than negative symptoms of psychosis (estimate, 0.36 [95% CI, 0.12-0.61]; P = .004). There was significant inconsistency in outcomes between studies (I2 range, 77%-83%). Bolus followed by constant infusion increased ketamine's association with positive symptoms relative to infusion alone (effect size, 1.63 [95% CI, 1.36-1.90] vs 0.84 [95% CI, 0.35-1.33]; P = .006). Single-day study design increased ketamine's ability to generate total symptoms (effect size, 2.29 [95% CI, 1.69-2.89] vs 1.39 [95% CI, 1.12-1.66]; P = .007), but age and sex did not moderate outcomes. Insufficient studies were available for meta-analysis of studies in schizophrenia. Of these studies, 2 found a statistically significant increase in symptoms with ketamine administration in total and positive symptoms. Only 1 study found an increase in negative symptom severity with ketamine.

Conclusions and Relevance

This study found that acute ketamine administration was associated with schizophrenia-like or psychotomimetic symptoms with large effect sizes, but there was a greater increase in positive than negative symptoms and when a bolus was used. These findings suggest that bolus doses should be avoided in the therapeutic use of ketamine to minimize the risk of inducing transient positive (psychotic) symptoms.

Ketamine induced changes in regional cerebral blood flow, interregional connectivity patterns, and glutamate metabolism

Several imaging studies have attempted to characterize the contribution of glutamatergic dysfunction to functional dysconnectivity of large-scale brain networks using ketamine models. However, findings from BOLD imaging studies are conflicting, in part because the signal stems from a complex interaction between blood flow, blood volume, and oxygen consumption. We used arterial spin labelling imaging to measure regional cerebral blood flow (rCBF) in a group of healthy volunteers during a saline and during a ketamine infusion. We examined changes in rCBF and interregional connectivity patterns, as well as their associations with clinical symptom severity and Glx (glutamate + glutamine) assessed with magnetic resonance spectroscopy. We report a regionally selective pattern of rCBF changes following ketamine administration and complex changes in interregional connectivity patterns. We also found that the increase in rCBF in the bilateral putamen and left hippocampus was positively correlated with ketamine induced clinical symptom severity while anterior cingulate rCBF during the ketamine challenge was negatively correlated with change in hippocampal Glx. Our study adds to the efforts to empirically confirm putative links between an NMDA receptor blockage and dysconnectivity of large-scale brain networks, specifically the salience, executive control and default mode networks, suggesting that a glutamatergic imbalance may contribute to dysconnectivity. Development of glutamatergic compounds that alleviate disease burden, possibly through normalizing glutamate excess related increased rCBF, is direly needed.

Neurometabolic abnormalities in the associative striatum in antipsychotic-naïve first episode psychosis patients

Schizophrenia is a chronic, often progressive, disorder. Understanding the underlying neurobiology present in the early stages of the illness is as a pivotal step in designing targeted interventions aimed at arresting disease progression. The aim of our study was to examine neurometabolic changes in the dopamine rich associative striatum in medication-naïve first episode psychosis (FEP). We quantified neurometabolites in 14 FEP and 18 healthy controls (HC) matched on key demographic characteristics. Spectra from the voxel in the left associative striatum were acquired using a PRESS sequence (TR/TE = 2000/80 ms; 512 averages). MRS data were quantified in the time domain with AMARES in jMRUI. Choline was significantly elevated in FEP compared to HC. No significant alterations in other metabolites were observed. We did not observe correlations between metabolite levels and clinical characteristics in FEP. Here, we demonstrated elevated choline and a disruption of the relationship between N-acetyl-aspartate and Glx (glutamate + glutamine) in medication-naïve FEP patients in the left striatum indicating possible mitochondrial, membrane and glial dysfunction as an underlying pathological phenomenon. In addition, striatal choline shows promise as a biomarker for FEP that may have utility in clinical trials investigating target engagement in experimental regimens.

Approach to the Agitated Emergency Department Patient

BACKGROUND

Acute agitation is a common occurrence in the emergency department (ED) that requires rapid assessment and management.

OBJECTIVE

This review provides an evidence-based summary of the current ED evaluation and management of acute agitation.

DISCUSSION

Acute agitation is an increasingly common presentation to the ED and has a broad differential diagnosis including metabolic, neurologic, infectious, toxicologic, and psychiatric etiologies. Missed diagnosis of a dangerous etiology of the patient's agitation may result in severe morbidity and mortality. Assessment and management of the agitated patient should occur concurrently. Focused history and physical examination are recommended, though control of the patient's agitation may be required. All patients should receive a point-of-care glucose test, with additional testing depending upon the specific patient presentation. Initial management should involve verbal de-escalation techniques, followed by pharmacologic interventions, with physical restraints reserved as a last resort. Pharmacologic options include first-generation antipsychotics, second-generation antipsychotics, benzodiazepines, and ketamine. Finally, the management of pediatric, pregnant, and elderly patients warrants special consideration.

CONCLUSION

Acute agitation is an important presentation that requires prompt recognition and treatment. A focused and thorough examination coupled with appropriate management strategies can assist emergency clinicians to safely and effectively manage these patients.

Pilot Randomized Controlled Trial of Titrated Subcutaneous Ketamine in Older Patients with Treatment-Resistant Depression

OBJECTIVE

To assess the efficacy and safety of subcutaneous ketamine for geriatric treatment-resistant depression. Secondary aims were to examine if repeated treatments were safe and more effective in inducing or prolonging remission than a single treatment.

METHODS

In this double-blind, controlled, multiple-crossover study with a 6-month follow-up (randomized controlled trial [RCT] phase), 16 participants (≥60 years) with treatment-resistant depression who relapsed after remission or did not remit in the RCT were administered an open-label phase. Up to five subcutaneous doses of ketamine (0.1, 0.2, 0.3, 0.4, and 0.5 mg/kg) were administered in separate sessions (≥1 week apart), with one active control (midazolam) randomly inserted (RCT phase). Twelve ketamine treatments were given in the open-label phase. Mood, hemodynamic, and psychotomimetic outcomes were assessed by blinded raters. Remitters in each phase were followed for 6 months.

RESULTS

Seven of 14 RCT-phase completers remitted with ketamine treatment. Five remitted at doses below 0.5 mg/kg. Doses ≥ 0.2 mg/kg were significantly more effective than midazolam. Ketamine was well tolerated. Repeated treatments resulted in higher likelihood of remission or longer time to relapse.

CONCLUSION

Results provide preliminary evidence for the efficacy and safety of ketamine in treating elderly depressed. Dose titration is recommended for optimizing antidepressant and safety outcomes on an individual basis. Subcutaneous injection is a practical method for giving ketamine. Repeated treatments may improve remission rates (clinicaltrials.gov; NCT01441505).

Ketamine modulates hippocampal neurochemistry and functional connectivity: a combined magnetic resonance spectroscopy and resting-state fMRI study in healthy volunteers

A growing body of evidence suggests glutamate excess in schizophrenia and that N-methyl-d-aspartate receptor (NMDAR) hypofunction on γ-aminobutyric acid (GABA) interneurons disinhibiting pyramidal cells may be relevant to this hyperglutamatergic state. To better understand how NMDAR hypofunction affects the brain, we used magnetic resonance spectroscopy and resting-state functional magnetic resonance imaging (MRI) to study the effects of ketamine on hippocampal neurometabolite levels and functional connectivity in 15 healthy human subjects. We observed a ketamine-induced increase in hippocampal Glx (glutamate+glutamine; F=3.76; P=0.04), a decrease in fronto-temporal (t=4.92, P_FDR<0.05, k_E=2198, x=-30, y=52, z=14) and temporo-parietal functional connectivity (t=5.07, P_FDR<0.05, k_E=6094, x=-28, y=-36, z=-2), and a possible link between connectivity changes and elevated Glx. Our data empirically support that hippocampal glutamatergic elevation and resting-state network alterations may arise from NMDAR hypofunction and establish a proof of principle whereby experimental modelling of a disorder can help mechanistically integrate distinct neuroimaging abnormalities in schizophrenia.

Effects of sex and DTNBP1 (dysbindin) null gene mutation on the developmental GluN2B-GluN2A switch in the mouse cortex and hippocampus

BACKGROUND

Neurodevelopmental disorders such as autism spectrum disorders and schizophrenia differentially impact males and females and are highly heritable. The ways in which sex and genetic vulnerability influence the pathogenesis of these disorders are not clearly understood. The n-methyl-d-aspartate (NMDA) receptor pathway has been implicated in schizophrenia and autism spectrum disorders and changes dramatically across postnatal development at the level of the GluN2B-GluN2A subunit "switch" (a shift from reliance on GluN2B-containing receptors to reliance on GluN2A-containing receptors). We investigated whether sex and genetic vulnerability (specifically, null mutation of DTNBP1 [dysbindin; a possible susceptibility gene for schizophrenia]) influence the developmental GluN2B-GluN2A switch.

METHODS

Subcellular fractionation to enrich for postsynaptic density (PSD), together with Western blotting and kinase assay, were used to investigate the GluN2B-GluN2A switch in the cortex and hippocampus of male and female DTNBP1 null mutant mice and their wild-type littermates. Main effects of sex and DTNBP1 genotype, and interactions with age, were assessed using factorial ANOVA.

RESULTS

Sex differences in the GluN2B-GluN2A switch emerged across development at the frontal cortical synapse, in parameters related to GluN2B. Males across genotypes displayed higher GluN2B:GluN2A and GluN2B:GluN1 ratios (p < 0.05 and p < 0.01, respectively), higher GluN2B phosphorylation at Y1472 (p < 0.01), and greater abundance of PLCγ (p < 0.01) and Fyn (p = 0.055) relative to females. In contrast, effects of DTNBP1 were evident exclusively in the hippocampus. The developmental trajectory of GluN2B was disrupted in DTNBP1 null mice (genotype × age interaction p < 0.05), which also displayed an increased synaptic GluN2A:GluN1 ratio (p < 0.05) and decreased PLCγ (p < 0.05) and Fyn (only in females; p < 0.0005) compared to wild-types.

CONCLUSIONS

Sex and DTNBP1 mutation influence the GluN2B-GluN2A switch at the synapse in a brain-region-specific fashion involving pY1472-GluN2B, Fyn, and PLCγ. This highlights the possible mechanisms through which risk factors may mediate their effects on vulnerability to disorders of NMDA receptor dysfunction.

Has psychiatry tamed the "ketamine tiger?" Considerations on its use for depression and anxiety

Ketamine has been available for approximately 50 years as an anesthetic agent. It is known to have potent effects on the central nervous system glutamatergic system, in particular blockade of N-methyl-D-aspartate (NMDA) receptors. Based upon pre-clinical evidence of involvement of the glutamatergic system in mood disorders, studies have been undertaken to test the antidepressant properties of ketamine. Several well-controlled studies, along with open-label case series, have established that ketamine can have rapid antidepressant effects. Additionally, data exist showing benefits of ketamine in post-traumatic stress disorder as well as obsessive compulsive disorder. However, improvements in these conditions tend to be short-lived with single infusions of ketamine. Of concern, ketamine has been associated with neurotoxicity in pre-clinical rodent models and is well-known to cause psychotomimetic effects and addiction in humans. While ketamine has been proven safe for use in sub-anesthetic doses administered once or a few times, the safety profile of prolonged use has not been established. Aspects of safety, possible mechanisms of action, and future directions of ketamine research are discussed in addition to the clinical literature on its use in psychiatric conditions.

A Ketamine Protocol and Intubation Rates for Psychiatric Air Medical Retrieval

OBJECTIVE

The air medical transfer of psychiatric patients with acute agitation is a regular requirement in only a few countries, with ours (Australia) being one of them. The optimal strategy has yet to be well described, ranging from physical restraints to general anesthesia with endotracheal intubation. In an Australian air medical service, Royal Flying Doctor Service (Queensland Section) rates of endotracheal intubation required for patient management were retrospectively compared before and after implementation of a ketamine sedation protocol for this patient population.

METHODS

A systematic retrospective review was performed using 9 years of data included in the Royal Flying Doctor Service (Queensland Section) electronic database (2004-2013). Coding for mental health as the primary diagnosis and intubation were the search criteria.

RESULTS

A total of 1,478 patients were transferred during the study period, with 44 requiring intubation. This equates to intubation rates of 3.5% before protocol use compared with 2.3% after protocol implementation.

CONCLUSION

In an Australian air medical service, the implementation of a ketamine sedation protocol for the management of the acutely agitated patient requiring air transfer has reduced the number of intubations in this patient group.

[Ketamine as antidepressant: the current study situation]

The treatment of depressive episodes is characterized by a delay in response of antidepressant medications and high rates of therapeutic failure. In recent years several open and five controlled trials have demonstrated the antidepressant efficacy of ketamine for major depression. In addition a recent study established the utility of nasal ketamine which may render the necessity of intravenous administration obsolete. The current state of evidence is reviewed and discussed.

Preliminary evaluation of clinical outcome and safety of ketamine as an anesthetic for electroconvulsive therapy in schizophrenia

OBJECTIVES

Electroconvulsive therapy (ECT) is an effective and safe option in the treatment of affective disorders and schizophrenia. One parameter known to influence ECT treatment efficacy is the choice of narcotic, and ketamine has emerged as an interesting alternative to conventional anaesthetics like barbiturates since it does not negatively influence seizure threshold. However, due to the potential to provoke dissociative symptoms, ketamine anaesthesia is rather hesitantly used in schizophrenia patients for fear of causing disease exacerbation.

METHODS

We retrospectively investigated clinical outcome and safety in patients treated with ECT for schizophrenia and receiving ketamine anaesthesia, either exclusively or as switch from another narcotic and compared seizure parameters to a group of ECT-treated schizophrenia patients with thiopental anaesthesia.

RESULTS

In none of the six patients undergoing ECT with ketamine did we observe disease exacerbation, and except for one patient, all patients responded or remitted under ECT. A preliminary analysis of seizure parameters shows an association with longer seizures in patients exclusively receiving ketamine.

CONCLUSIONS

While the small sample size and retrospective character are limitations of our study, our preliminary results nonetheless challenge wide-spread preconceptions about the use of ketamine in schizophrenia patients and encourage further research into the option of using ketamine anaesthesia for ECT.

A review of ketamine in affective disorders: current evidence of clinical efficacy, limitations of use and pre-clinical evidence on proposed mechanisms of action

INTRODUCTION

Recent research has seen low-dose ketamine emerge as a novel, rapid-acting antidepressant. Ketamine, an N-methy-d-aspartate (NMDA) receptor antagonist, leads to effects on the glutamatergic system and abnormalities in this neurotransmittor system are present in depression. This article aims to (1) review the clinical literature on low-dose ketamine as a rapid-acting antidepressant in affective disorders, (2) provide a critical overview of the limitations of ketamine and research attempts to overcome these (3) discuss the proposed mechanisms of action of ketamine and (4) point towards future research directions.

METHOD

The electronic database Pubmed, Web of Science and sciencedirect were searched using the keywords: ketamine, N-methyl-d-aspartate receptor antagonist, rapid-acting antidepressant, depression, treatment-resistant depression, bipolar depression, suicidal ideation, electroconvulsive therapy, mechanism of action.

RESULT

The literature demonstrates evidence supporting a rapid-acting antidepressant effect of low-dose intravenous ketamine in major depressive disorder, in bipolar depression and in depression with suicidal ideation. There are mixed results as to whether ketamine leads to a reduction in time to remission in patients undergoing electroconvulsive therapy (ECT). Efforts to unravel ketamine's therapeutic mechanism of action have implicated the mammalian target of rapamycin (mTOR)-dependent synapse formation in the rat prefrontal cortex, eukaryotic elongation factor 2 phosphorylation (p-eEF2) and glycogen synthase kinase (GSK-3). Ketamine's limiting factors are the transient nature of its antidepressant effect and concerns regarding abuse, and research efforts to overcome these are reviewed.

CONCLUSION

Current and future research studies are using ketamine as a promising tool to evaluate the glutamatergic neurotransmittor system to learn more about the pathophysiology of depression and develop more specific rapid-acting antidepressant treatments.

Rapid-acting glutamatergic antidepressants: the path to ketamine and beyond

Traditional antidepressants require many weeks to reveal their therapeutic effects. However, the widely replicated observation that a single subanesthetic dose of the N-methyl-D-aspartate glutamate receptor antagonist ketamine produced meaningful clinical improvement within hours, suggested that rapid-acting antidepressants might be possible. The ketamine studies stimulated a new generation of basic antidepressant research that identified new neural signaling mechanisms in antidepressant response and provided a conceptual framework linking a group of novel antidepressant mechanisms. This article presents the path that led to the testing of ketamine, considers its promise as an antidepressant, and reviews novel treatment mechanisms that are emerging from this line of research.

Relationship of ketamine's plasma metabolites with response, diagnosis, and side effects in major depression

BACKGROUND

Ketamine has rapid antidepressant effects lasting as long as 1 week in patients with major depressive disorder (MDD) and bipolar depression (BD). Ketamine is extensively metabolized. This study examined the relationship between ketamine metabolites and response, diagnosis, and psychotomimetic symptoms in MDD and BD patients.

METHODS

Following a 40-minute ketamine infusion (.5 mg/kg), plasma samples were collected at 40, 80, 110, and 230 minutes and day 1 postinfusion in 67 patients currently experiencing a major depressive episode (MDD, n = 45; BD, n = 22). Concentrations of ketamine, norketamine (NK), dehydronorketamine (DHNK), six hydroxynorketamine metabolites (HNK), and hydroxyketamine (HK) were measured. Plasma concentrations were analyzed by diagnostic group and correlated with patients' depressive, psychotic, and dissociative symptoms. The relationship between cytochrome P450 gene polymorphisms and metabolites, response, and diagnosis was also examined.

RESULTS

Ketamine, NK, DHNK, four of six HNKs, and HK were present during the first 230 minutes postinfusion. Patients with BD had higher plasma concentrations of DHNK, (2S,6S;2R,6R)-HNK, (2S,6R;2R,6S)-HNK, and (2S,5S;2R,5R)-HNK than patients with MDD, who, in turn, had higher concentrations of (2S,6S;2R,6R)-HK. Higher (2S,5S;2R,5R)-HNK concentrations were associated with nonresponse to ketamine in BD patients. Dehydronorketamine, HNK4c, and HNK4f levels were significantly negatively correlated with psychotic and dissociative symptoms at 40 minutes. No relationship was found between cytochrome P450 genes and any of the parameters examined.

CONCLUSIONS

A diagnostic difference was observed in the metabolism and disposition of ketamine. Concentrations of (2S,5S;2R,5R)-HNK were related to nonresponse to ketamine in BD. Some hydroxylated metabolites of ketamine correlated with psychotic and dissociative symptoms.

Meta-analysis of the efficacy of adjunctive NMDA receptor modulators in chronic schizophrenia

BACKGROUND

Based on the glutamatergic NMDA receptor hypofunction theory of schizophrenia, NMDA receptor modulators (NMDARMs) may have therapeutic potential in the treatment of schizophrenia.

OBJECTIVE

This meta-analysis aimed to evaluate the potential of modulators of the NMDA receptor as adjunctive therapy for schizophrenia, using the results from published trials.

DATA SOURCES

A primary electronic search for controlled clinical trials using NMDARMs in schizophrenia was conducted on the PubMed, Cochrane Library, EMBASE, CINAHL® and PsycINFO databases. A secondary manual search of references from primary publications was also performed.

STUDY SELECTION

Inclusion criteria were the application of an established method of diagnosis, randomized case assignment, comparison of NMDARM add-on therapy with placebo, and double-blind assessment of symptoms in chronic schizophrenia using standardized rating scales. Results were based on a total sample size of 1253 cases from 29 trials that fulfilled the specified criteria.

DATA EXTRACTION

Scores on rating scales or on their relevant subscales were obtained for all selected studies from published results for the minimum dataset to compute the difference between post- and pre-trial scores and their pooled standard deviation for NMDARM add-on therapy and placebo groups for negative, positive and total symptoms.

RESULTS

A negative standardized mean difference (SMD) indicates therapeutic benefit in favour of NMDARM add-on therapy and all SMD results mentioned here are statistically significant. The overall effect size for NMDARMs as a group was small for negative (SMD -0.27) and medium for total (SMD -0.40) symptoms of chronic schizophrenia. Subgroup analysis revealed medium effect sizes for D-serine and N-acetyl-cysteine (NAC) for negative (SMD -0.53 and -0.45, respectively) and total (SMD -0.40 and -0.64, respectively) symptoms, and for glycine (SMD -0.66) and sarcosine (SMD -0.41) for total symptoms. As adjuvants to non-clozapine antipsychotics, additional therapeutic benefits were observed for NMDARM as a group (SMD -0.14) and glycine (SMD -0.54) for positive symptoms; D-serine (SMD -0.54), NAC (SMD -0.45) and sarcosine (SMD -0.39) for negative symptoms; and NMDARM as a group (SMD -0.38), D-serine (SMD -0.40), glycine (SMD -1.12), NAC (SMD -0.64) and sarcosine (SMD -0.53) for total symptoms. When added to clozapine, none of the drugs demonstrated therapeutic potential, while addition of glycine (SMD +0.56) worsened positive symptoms.

CONCLUSIONS

Taking into consideration the number of trials and sample size in subgroup analyses, D-serine, NAC and sarcosine as adjuncts to non-clozapine antipsychotics have therapeutic benefit in the treatment of negative and total symptoms of chronic schizophrenia. While glycine improves positive and total symptoms as an adjuvant to non-clozapine antipsychotics, it worsens them when added to clozapine.

The Therapeutic Potential of D-Amino Acid Oxidase (DAAO) Inhibitors

D-amino acid oxidase (DAAO) is a flavoenzyme that degrades D-amino acids through the process of oxidative deamination. DAAO regulation of D-amino acid levels has been associated with several physiological processes ranging from hormone secretion to synaptic transmission and cognition. Recent genetic studies have identified a mutation on chromosome 13 in schizophrenia patients that encodes two gene products (G30 and G72) that are associated with DAAO. Furthermore, DAAO expression and enzyme activity has been reported to be increased in post mortem brain tissue samples from patients with schizophrenia compared to healthy controls. D-serine, a D-amino acid that is regulated by DAAO, is a potent, endogenous co-agonist of the N-methyl-D-aspartic acid (NMDA) receptor. Because NMDA receptor dysfunction is thought to be involved in the positive (psychotic), negative and cognitive symptoms in schizophrenia, there has been much interest in developing potent and selective DAAO inhibitors for the treatment of this disease. Several research reports have been published that describe the synthesis and biological effects of novel, selective, small molecule inhibitors of DAAO. Many of these compounds have been shown, when given systemically, to increase D-serine concentrations in the blood and brain. However, the efficacy of these compounds in behavioral assays that measure antipsychotic potential and pro-cognitive effects in laboratory animals has been inconsistent. This article highlights and reviews research advances for DAAO inhibitors published in peer reviewed journals.

Safety and efficacy of repeated-dose intravenous ketamine for treatment-resistant depression

BACKGROUND

A single subanesthetic (intravenous) IV dose of ketamine might have rapid but transient antidepressant effects in patients with treatment-resistant depression (TRD). Here we tested the tolerability, safety, and efficacy of repeated-dose open-label IV ketamine (six infusions over 12 days) in 10 medication-free symptomatic patients with TRD who had previously shown a meaningful antidepressant response to a single dose.

METHODS

On day 1, patients received a 40-min IV infusion of ketamine (.5 mg/kg) in an inpatient setting with continuous vital-sign monitoring. Psychotomimetic effects and adverse events were recorded repeatedly. The primary efficacy measure was change from baseline in the Montgomery-Asberg Depression Rating Scale (MADRS) score. If patients showed a > or =50% reduction in MADRS scores on day 2, they received five additional infusions on an outpatient basis (days 3, 5, 8, 10, and 12). Follow-up visits were conducted twice-weekly for > or =4 weeks or until relapse.

RESULTS

Ketamine elicited minimal positive psychotic symptoms. Three patients experienced significant but transient dissociative symptoms. Side effects during and after each ketamine infusion were generally mild. The response criterion was met by nine patients after the first infusion as well as after the sixth infusion. The mean (SD) reduction in MADRS scores after the sixth infusion was 85% (12%). Postketamine, eight of nine patients relapsed, on average, 19 days after the sixth infusion (range 6 days-45 days). One patient remained antidepressant-free with minimal depressive symptoms for >3 months.

CONCLUSIONS

These pilot findings suggest feasibility of repeated-dose IV ketamine for the acute treatment of TRD.

Research risk for persons with psychiatric disorders: a decisional framework to meet the ethical challenge

OBJECTIVE

There is a lack of consensus on how to evaluate the risk of research studies conducted with persons who have psychiatric disorders. The authors reviewed research on vulnerability, risk, and procedures to mitigate risk in studies with this population to help inform evaluation of such research.

METHODS

Searches of MEDLINE (1966-2006), PsycINFO (1967-2006), and Google Scholar used combinations of the terms mental illness, vulnerable, psychiatric, schizophrenia, and depression combined with terms such as research risk, vulnerability, research harm, capacity, risk, and mitigation of risk. Articles were identified from reference lists, and additional searches used terms from identified articles.

RESULTS

Evidence for two types of vulnerability--capacity based and power based--is presented, which supports the notion of vulnerability as a state, rather than a trait, among persons with psychiatric disorders. Three categories of risk are described--minimal risk, minor increment over minimal risk, and greater than minor increment. Evidence shows that many common types of studies pose risk in the first two categories when conducted with this population. The literature also describes procedures for reducing vulnerability and mitigating risk that should be considered in study evaluations. The authors offer a framework for evaluating the category of risk posed by a study.

CONCLUSIONS

Although more research is needed, there is sufficient evidence that many common types of research present minimal risk or only a minor increment over minimal risk for large segments of the population of persons with psychiatric disorders, as they do for persons in the general population.

Models of schizophrenia in humans and animals based on inhibition of NMDA receptors

The research of the glutamatergic system in schizophrenia has advanced with the use of non-competitive antagonists of glutamate NMDA receptors (phencyclidine, ketamine, and dizocilpine), which change both human and animal behaviour and induce schizophrenia-like manifestations. Models based on both acute and chronic administration of these substances in humans and rats show phenomenological validity and are suitable for searching for new substances with antipsychotic effects. Nevertheless, pathophysiology of schizophrenia remains unexplained. In the light of the neurodevelopmental model of schizophrenia based on early administration of NMDA receptor antagonists it seems that increased cellular destruction by apoptosis or changes in function of glutamatergic NMDA receptors in the early development of central nervous system are decisive for subsequent development of psychosis, which often does not manifest itself until adulthood. Chronic administration of antagonists initializes a number of adaptation mechanisms, which correlate with findings obtained in patients with schizophrenia; therefore, this model is also suitable for research into pathophysiology of this disease.

Psychiatric safety of ketamine in psychopharmacology research

RATIONALE

A growing number of investigators are studying ketamine effects in healthy human subjects, but concerns remain about its safety as a research tool. Therefore, it is timely to revisit the safety of subanesthetic doses of ketamine in experimental psychopharmacology studies.

OBJECTIVE

To report on the safety of laboratory studies with subanesthetic doses of ketamine in healthy humans using an existing dataset.

MATERIALS AND METHODS

Medically healthy subjects with no personal or familial Axis I psychotic spectrum disorders were administered subanesthetic doses of ketamine by intravenous infusion in a series of clinical investigations from 1989 to 2005. The safety of ketamine administration was monitored in these subjects.

RESULTS

Four hundred and fifty subjects received at least one dose of active ketamine. Eight hundred and thirty three active ketamine and 621 placebo infusions were administered. Ten adverse mental status events were documented in nine subjects/infusions that were deemed related to ketamine administration (2% of subjects, 1.45% of infusions). All but one adverse reaction resolved by the end of the test session. The side effects in the remaining individual were no longer clinically significant within 4 days of the test session. No residual sequelae were observed.

CONCLUSION

Ketamine administration at subanesthetic doses appears to present an acceptable level of risk for carefully screened populations of healthy human subjects in the context of clinical research programs that intensively monitor subjects throughout their study participation.

Ketamine : from medicine to misuse

This review describes the medical, research and recreational uses of ketamine, an anaesthetic derivative of phencyclidine that has dissociative, analgesic and psychedelic properties. Ketamine has a complex mechanism of action that is further complicated by stereoselectivity; however, antagonism of glutamate NDMA receptors is thought to underlie its analgesic, dissociative and neuroprotective effects. While ketamine use in medical and veterinary settings is well documented and has a good safety record, the increase in its unregulated use outside of such controlled environments is a cause for concern. The impact on higher centres in the brain, particularly altered perception of auditory, visual and painful stimuli, results in a general lack of responsive awareness that puts the recreational user at (often unrecognised) risk of personal harm. The perceptual and mood changes observed in those who have consumed ketamine are highly sensitive to age, dose, route of administration, previous experience and setting. At low doses, stimulant effects predominate and the effect of environmental conditions are significant; with higher doses, psychedelic effects predominate and the effect of the environment diminishes. The potential of ketamine as a novel clinical and research tool is matched by its abuse potential outside medical settings.

Absence of behavioral sensitization in healthy human subjects following repeated exposure to ketamine

RATIONALE

Sensitization to the effects of N-methyl-D-aspartate (NMDA) glutamate receptor antagonists is robust in animals. However, the applicability of this model to humans is unclear because it currently rests on highly confounded retrospective studies of individuals who experienced protracted psychoses following repeated binges with NMDA receptor antagonists.

OBJECTIVES

The purpose of the current study was to determine whether there was evidence of sensitization to the behavioral effects of ketamine in healthy human subjects with repeated exposure to this drug.

METHODS

Data were studied from 295 healthy human subjects who participated in one or more of 11 separate studies that involved ketamine administration over 14 years. Positive and negative symptoms (Brief Psychiatric Rating Scale: BPRS), perceptual alterations (Clinician-Administered Dissociative States Scale: CADSS), and "high" and "anxiety" states (Visual Analog Scale: VAS) that were measured in all studies were included as outcome measures.

RESULTS

After including the number of previous exposures, number of previous studies, and time since first exposure as variables, repeated exposure to ketamine did not result in increased behavioral responses, suggestive of behavioral sensitization.

CONCLUSIONS

The current data do not provide evidence that repeated exposure to ketamine, albeit limited, is associated with sensitization to the behavioral effects of ketamine.

Evaluating Glutamatergic Transmission in Schizophrenia

Our findings with schizophrenia and the glutamate system have relied on the characterization of the clinical response of patients to ketamine and their functional brain imaging response (rCBF) to the drug. Prior to the human studies reported here, we had evaluated the region activation characteristics and pharmacology of PCP and its congener MK 801 in animals. What I will report in this paper has been individually reported elsewhere but brought together here in a new synthesis.

N-methyl-D-aspartate receptor in working memory impairments in schizophrenia: event-related potential study of late stage of working memory process

Working memory (WM) deficit in schizophrenic patients has been well established. Still, underlying biological substrate of the impairment is not clear. Among neurotransmitter hypotheses of schizophrenia, N-methyl-D-aspartate (NMDA) receptor model is mostly supported, considering that NMDA receptor antagonist can elicit both psychosis and cognitive impairment observed in schizophrenic patients. In current study, to test the neuropsychological and the electrophysiological effects of NMDA receptor in WM, event-related potentials (ERPs) of Sternberg's short-term memory scanning task (SMST) were analyzed in 10 healthy subjects under intravenous administration of a subanesthetic dose of ketamine (0.65 mg/kg/h) or placebo (normal saline). Late positive component (LPC) of ERP was hypothesized to reflect later stage of WM. Brief Psychiatric Rating Scale score was significantly increased (t=-5.75, df=9, P<.001) and correct response rate was significantly decreased (t=2.21, df=9, P=.054) after ketamine administration. Neither reaction time nor LPC latency, which reflect memory scanning time, was changed. Amplitude of LPC was significantly reduced after ketamine administration (z=-2.31, number of observations=120, P=.021). In conclusion, NMDA receptor antagonist administration elicited WM deficit both in behavioral and electrophysiological level. Electrophysiological component reflecting later stage of WM was impaired by NMDA antagonist.

Effects of subanesthetic doses of ketamine on sensorimotor information processing in healthy subjects

Ketamine, an antagonist N-Methyl-D-Aspartate receptor, induces a broad range of anomalies in healthy subjects similar to those observed in psychosis. Previous studies have shown that information sensorimotor processing was impaired in patients with schizophrenia. The aim of the study was to assess the effects of subanesthetic doses of ketamine on behavior symptoms and information processing in healthy volunteers. A double-blind, crossover, placebo-controlled study was performed with eight subjects. Brief Psychiatric Rating Scale, Scale for the Assessment of Negative Symptoms, and Scale for the Assessment of Positive Symptoms assessed behavior changes. Information processing was assessed using a choice reaction time. Three experimental factors (stimulus intensity, stimulus response compatibility, and foreperiod duration) chosen to affect a different stage of information processing were manipulated. Our study has demonstrated that administration of ketamine produced significant effects on Brief Psychiatric Rating Scale, Scale for the Assessment of Negative Symptoms, and Scale for the Assessment of Positive Symptoms scores. Results on choice reaction time demonstrated a significant longer reaction time under ketamine. Effects of stimulus intensity and compatibility stimulus response were similar under ketamine and under placebo. Moreover, there was a specific interaction between ketamine and foreperiod. This interaction indicated that foreperiod's effect was more prolonged under ketamine (29 ms) than under placebo (17 ms). These results showed that the clinical effects of ketamine were associated with schizophrenic-like impairments on choice reaction time in healthy subjects.

A comparison of symptom provocation procedures in psychiatry and other areas of medicine: implications for their ethical use in research

BACKGROUND

Symptom provocation is used to study a wide variety of medical disorders. In contrast to other areas of medicine, the application of these procedures to the study of mental disease has generated significant scientific, political, and public debate. Purported differences include an overabundance of these procedures in psychiatry and a lack of diagnostic and therapeutic utility. Accurate appraisal of these research designs is needed to address scientific merit and ethical concerns. This article provides a general review of challenge studies in several areas of medical research, compares purposes and methods to those used in psychiatry, and ascertains whether fundamental differences exist.

METHODS

In total, 655 challenge studies were identified using MEDLINE and PsychInfo Boolean key word searches. Information was collected from each study including the year of publication, whether subjects were healthy or patient volunteers, the disease being studied, and the study purpose (e.g., to study pathophysiology, test treatment efficacy, or diagnosis of a disorder).

RESULTS

Differences in study design, purpose, and frequency of studies across time were similar for medical and psychiatric diseases.

CONCLUSIONS

Given extensive similarity in purpose and procedures, why are psychiatric challenge studies being subjected to public criticism and special review and approval procedures? Several relevant issues are addressed including risk, scientific merit, and clinical application.

Emerging targets for the treatment of depressive disorder

New agents offering novel mechanisms of action are required in the treatment of depressive disorder. Established agents targeting monoamine systems are unsatisfactory because of full and partial treatment resistance, delay in the onset of their effect and the occurrence of side effects. The monoamine hypothesis of depression is now recognised to provide an incomplete explanation of the pathophysiology of depression. New theories have recently developed and new targets for treatment have emerged. We briefly review some important candidate systems and therapeutic targets in depression: the hypothalamic-pituitary-adrenal axis (HPA) and the glucocorticoid and corticotrophin-releasing factor receptors, synaptic plasticity and neurotrophins and the N-methyl-D-aspartate (NMDA) receptor. The putative role of the neuropeptides substance P and neuropeptide Y, the nicotinic system and the potential therapeutic benefits of cannabinoids are also reviewed. Vagal nerve stimulation (VNS) and transcranial magnetic stimulation, serendipitous advances in treatment, are discussed briefly.