Repeated intravenous infusions of ketamine: Neurocognition in patients with anxious and nonanxious treatment-resistant depression

Long-Term Cognitive Outcomes of Esketamine Nasal Spray in Treatment-Resistant Depression: A Preliminary Report

Background/Objectives: Ketamine/esketamine has a rapid/robust antidepressant effect on treatment-resistant depression (TRD). However, its long-term cognitive effects remain unclear. In this study, we investigated the potential cognitive effects of an esketamine spray on a series of TRD patients. Methods: We evaluated the cognitive performance of eight TRD patients subjected to an esketamine nasal spray as an adjunct treatment for six months. Cognitive assessments were performed before treatment initiation (T0) and at three (T3) and six (T6) months by an experienced neuropsychologist using a comprehensive neuropsychological battery. Depression severity was assessed by the Montgomery-Åsberg Depression Rating Scale. Changes in cognitive performance were analyzed by determining the bias between time points. To investigate the association between the severity of depression and performance on cognitive tests, we used correlation with correction for repeated measures and regression analysis with a general linear mixed model. We used the Tukey method to compare three estimates and the Dunnett method to compare two estimates. Results: Improvements in at least one test from T0 to T6 were found for attention, memory, and the executive functions of working memory, set-shifting, and inhibitory control. Most of the improvements had occurred by T3, but working memory and set-shifting improvements were significant only at T6. The severity of depression decreased significantly from T0 to T6, and most cognitive improvements were correlated with an improvement in depression severity. No test indicated a worsening of cognitive performance from T0 to T6. Conclusions: Our results suggest that the cognitive performance of TRD patients improved with long-term adjunct treatment with an esketamine nasal spray. Confirmatory studies are necessary.

Demographic and clinical predictors of response and remission in the treatment of major depressive disorder with ketamine and esketamine: A systematic review

Accumulating evidence supports the efficacy of (es)ketamine in the treatment of major depressive disorder (MDD), particularly treatment-resistant depression (TRD). Yet around 50% of the individuals with TRD do not respond to (es)ketamine. Elucidating predictors of response and remission could improve treatment outcomes at the individual level by defining subpopulations that are most likely to benefit from (es)ketamine. This systematic review outlines the predictive value of demographic and clinical characteristics for treatment outcomes of (es)ketamine in MDD. A systematic literature search was performed to retrieve studies investigating the association between baseline characteristics and the likelihood of achieving response and remission following (es)ketamine treatment in MDD. Forty-four studies investigating the association between response and remission and demographic variables, characteristics of the depressive episode, treatment resistance, psychiatric comorbidities, symptomatology, suicidal risk/attempts, family/personal history, medication use, somatic variables, personality traits, and neurocognitive performance were included. The predictive value of demographic and clinical variables for treatment outcomes of (es)ketamine was limited with either no significant relationship or inconsistent results. Findings provide preliminary support for a positive association of response with anhedonia, sleep disturbances, childhood physical abuse, obesity, openness, better episodic memory, and visual learning, poorer neurocognitive performance, slower processing speed, and lower attention, as well as a negative association with melancholic depression, benzodiazepine use, and metabolic syndrome. However, these characteristics have been investigated in a limited number of studies and warrant replication. These findings suggest that (es)ketamine represents a promising treatment prospect for individuals who present clinical characteristics that are often considered difficult to treat.

Cognitive changes in patients with unipolar TRD treated with IV ketamine: A systematic review

BACKGROUND

Unipolar treatment-resistant depression (MDD-TRD) is associated with neurocognitive impairment. Ketamine, an emerging treatment for MDD-TRD, may have neurocognitive benefits, but evidence remains limited.

METHODS

We conducted a systematic search on EMBASE, Google Scholar, PsycINFO, and PubMed and included studies exploring the cognitive effects of intravenous (IV) ketamine treatment in the management of MDD-TRD following the PRISMA guidelines. We analyzed cognitive scale score changes pre- and post-IV ketamine treatment and the quality of the evidence using the Cochrane risk of bias tool and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE).

RESULTS

Out of 1171 identified studies, fourteen studies were included in this study. Most studies reported positive cognitive outcomes post-ketamine treatment, including improvements in processing speed, working memory, verbal and visual memory, executive function, attention, emotional processing, and auditory verbal episodic memory. Variability existed, with one study reporting negative effects on verbal memory. Overall, studies exhibited a low risk of bias.

LIMITATIONS

Several limitations impacted the results observed, including confining our scope to articles in English, heterogeneity of the included studies, small sample sizes, and the predominance of a female, Western, and Caucasian population, constraining the generalizability of the findings.

CONCLUSIONS

IV ketamine treatment shows promise in improving neurocognitive function in MDD-TRD patients. However, further research is warranted to elucidate long-term effects, control for confounders such as concomitant medications, and explore neurocognitive subgroups within the TRD population. These findings underscore the need for comprehensive assessment and management of cognitive symptoms in TRD, informing future clinical practice.

Major challenges in youth psychopathology: treatment-resistant depression. A narrative review

Major depressive disorder (MDD) represents a major health issue in adolescents and young adults, leading to high levels of disability and profoundly impacting overall functioning. The clinical presentation of MDD in this vulnerable age group may slightly differ from what can be observed in adult populations, and psychopharmacological strategies do not always lead to optimal response. Resistance to antidepressant treatment has a prevalence estimated around 40% in youths suffering from MDD and is associated with higher comorbidity rates and suicidality. Several factors, encompassing biological, environmental, and clinical features, may contribute to the emergence of treatment-resistant depression (TRD) in adolescents and young adults. Furthermore, TRD may underpin the presence of an unrecognized bipolar diathesis, increasing the overall complexity of the clinical picture and posing major differential diagnosis challenges in the clinical practice. After summarizing current evidence on epidemiological and clinical correlates of TRD in adolescents and young adults, the present review also provides an overview of possible treatment strategies, including novel fast-acting antidepressants. Despite these pharmacological agents are promising in this population, their usage is expected to rely on risk-benefit ratio and to be considered in the context of integrated models of care.

Cognitive outcomes from the randomised, active-controlled Ketamine for Adult Depression Study (KADS)

BACKGROUND

Due to its rapid antidepressant effect, ketamine has recently been clinically translated for people with treatment-resistant depression. However, its cognitive profile remains unclear, particularly with repeated and higher doses. In the present study, we report the cognitive results from a recent large multicentre randomised controlled trial, the Ketamine for Adult Depression Study (KADS).

METHODS

In this randomised, double-blind, active-controlled, parallel group, multicentre phase 3 trial study we investigated potential cognitive changes following repeated treatment of subcutaneous racemic ketamine compared to an active comparator, midazolam, over 4 weeks, which involved two cohorts; Cohort 1 involved a fixed dose treatment protocol (0.5 mg/kg ketamine), Cohort 2 involved a dose escalation protocol (0.5-0.9 mg/kg) based on mood outcomes. Participants with treatment-resistant Major Depressive Disorder (MDD) were recruited from 7 mood disorder centres and were randomly assigned to receive ketamine (Cohort 1 n = 33; Cohort 2 n = 53) or midazolam (Cohort 1 n = 35; Cohort 2 n = 53) in a 1:1 ratio. Cognitive measurements were assessed at baseline and at the end of randomised treatment.

RESULTS

Results showed that in Cohort 1, there were no differences between ketamine and midazolam in cognitive outcomes. For Cohort 2, there was similarly no difference between conditions for cognitive outcomes.

LIMITATIONS

The study included two Cohorts with different dosing regimes.

CONCLUSIONS

The findings support the cognitive safety of repeated fixed and escalating doses at least in the short-term in people with treatment resistant MDD.

Recent Advances in the Treatment of Treatment-Resistant Depression: A Narrative Review of Literature Published from 2018 to 2023

PURPOSE OF REVIEW

We review recent advances in the treatment of treatment-resistant depression (TRD), a disorder with very limited treatment options until recently. We examine advances in psychotherapeutic, psychopharmacologic, and interventional psychiatry approaches to treatment of TRD. We also highlight various definitions of TRD in recent scientific literature.

RECENT FINDINGS

Recent evidence suggests some forms of psychotherapy can be effective as adjunctive treatments for TRD, but not as monotherapies alone. Little recent evidence supports the use of adjunctive non-antidepressant pharmacotherapies such as buprenorphine and antipsychotics for the treatment of TRD; side effects and increased medication discontinuation rates may outweigh the benefits of these adjunctive pharmacotherapies. Finally, a wealth of recent evidence supports the use of interventional approaches such as electroconvulsive therapy, ketamine/esketamine, and transcranial magnetic stimulation for TRD. Recent advances in our understanding of how to treat TRD have largely expanded our knowledge of best practices in, and efficacy of, interventional psychiatric approaches. Recent research has used a variety of TRD definitions for study inclusion criteria; research on TRD should adhere to inclusion criteria based on internationally defined guidelines for more meaningfully generalizable results.

Long-term quality of life after repeated ketamine infusions in anxious and nonanxious patients with depression

BACKGROUND

There have been many studies on the benefits of repeated ketamine infusions on patients' depression but few on the impact of ketamine on patients' long-term quality of life (QoL). This study investigated long-term QoL in individuals with depression, both anxious and nonanxious.

METHODS

A total of 107 individuals with a diagnosis of depression were included in the study. The patients were evaluated on Days 0, 13 and 26 and Months 6 and 9, and they received six ketamine infusions over the course of two weeks. The World Health Organization Quality of Life-BREF (WHOQOL-BREF) Scale and the Patient Health Questionnaire-9 (PHQ-9) Scale were used to measure depressive symptoms and QoL. Linear mixed models were used to evaluate depressive symptoms and QoL during ketamine treatment.

RESULTS

A total of 67.2 % of patients were diagnosed with anxious depression. In the long term, there were no significant differences in the time-by-group interactions for general QoL (F = 0.510; P = 0.676), physical QoL (F = 2.092; P = 0.102), psychological QoL (F = 0.102; P = 0.959), social QoL (F = 2.180; P = 0.091), or environmental QoL (F = 1.849; P = 0.139) between the two groups.

LIMITATIONS

The main limitation of this study is its open-label design.

CONCLUSION

The improvement in depression symptoms and QoL following ketamine treatment was not impacted by the presence or absence of anxiety in patients who were depressed prior to treatment. Only occasionally did depressed individuals with anxiety experience a worsening of their quality of life compared to those without anxiety.

Efficacy of repeated intravenous esketamine in adolescents with anxious versus non-anxious depression

Background

Patients with anxious major depressive disorder (MDD) are more likely to have poorer outcomes than those with non-anxious MDD. However, the effect of esketamine on adolescents with anxious versus non-anxious MDD has remained unknown.

Aims

We compared the efficacy of esketamine in adolescents with MDD and suicidal ideation, both anxious and non-anxious.

Methods

Fifty-four adolescents with anxious (n=33) and non-anxious (n=21) MDD received three infusions of esketamine 0.25 mg/kg or active-placebo (midazolam 0.045 mg/kg) over 5 days, with routine inpatient care and treatment. Suicidal ideation and depressive symptoms were assessed using the Columbia Suicide Severity Rating Scale and the Montgomery-Åsberg Depression Rating Scale. Multiple-sample proportional tests were used to compare the differences between groups on treatment outcomes 24 hours after the final infusion (day 6, primacy efficacy endpoint) and throughout the 4-week post-treatment (days 12, 19 and 33).

Results

In subjects who received esketamine, a greater number of patients in the non-anxious group than the anxious group achieved antisuicidal remission on day 6 (72.7% vs 18.8%, p=0.015) and day 12 (90.9% vs 43.8%, p=0.013), and the non-anxious group had a higher antidepressant remission rate compared with the anxious group on day 33 (72.7% vs 26.7%, p=0.045). No significant differences in treatment outcomes were observed between the anxious and non-anxious groups at other time points.

Conclusions

Three infusions of esketamine as an adjunct to routine inpatient care and treatment had a greater immediate post-treatment antisuicidal effect in adolescents with non-anxious MDD than in those with anxious MDD; however, this benefit was temporary and was not maintained over time.

Trial registration number

ChiCTR2000041232.

Neurocognitive effects of subanesthetic serial ketamine infusions in treatment resistant depression

INTRODUCTION

Ketamine treatment prompts a rapid antidepressant response in treatment-resistant depression (TRD). We performed an exploratory investigation of how ketamine treatment in TRD affects different cognitive domains and relates to antidepressant response.

METHODS

Patients with TRD (N = 66; 30 M/35F; age = 39.5 ± 11.1 years) received four ketamine infusions (0.5 mg/kg). Neurocognitive function and depressive symptoms were assessed at baseline, 24 h after the first and fourth ketamine infusion, and 5 weeks following end of treatment. Mixed effect models tested for changes in seven neurocognitive domains and antidepressant response, with post-hoc pairwise comparisons between timepoints, including follow-up. Relationships between change in neurocognitive function and antidepressant response over the course of treatment were tested with Pearson's correlation and mediation analyses. Associations between baseline neurocognitive performance and antidepressant response were tested with Pearson's correlation.

RESULTS

Significant improvements in inhibition, working memory, processing speed, and overall fluid cognition were observed after the first and fourth ketamine infusion. Improvements in processing speed and overall fluid cognition persisted through follow-up. Significant improvements in depressive symptoms reverted towards baseline at follow-up. Baseline working memory and change in inhibition were moderately correlated with antidepressant response, however, improvements in neurocognitive performance were statistically independent from antidepressant response.

CONCLUSION

Antidepressant ketamine leads to improved neurocognitive function, which persist for at least 5 weeks. Neurocognitive improvements observed appear independent of antidepressant response, suggesting ketamine may target overlapping but distinct functional brain systems. Limitations Research investigating repeated serial ketamine treatments is important to determine cognitive safety. This study is a naturalistic design and does not include placebo.

The therapeutic role of ketamine and esketamine in treating psychopathological domains of depression

Over the past two decades, ketamine has emerged as a novel effective and rapid-acting antidepressant. While the vast majority of studies on ketamine have focused on its ability to reduce the severity of depression broadly, its effectiveness in specific domains such as cognition, anhedonia, suicidality, and workplace/social/scholastic functionality has been neglected. Similarly, current treatments (e.g., SSRIs and SNRIs) aim to improve overall depression severity, which often results in the persistence of one or more residual symptom domains and prevents full recovery to premorbid functionality. In this review, we narratively synthesize the literature pertaining to the effectiveness of ketamine in treating key domains of depressive symptomatology (i.e., cognition, anhedonia, suicidality, and psychosocial functionality). Our findings suggest that ketamine is effective across domains varyingly, with the strongest evidence being for its ability to reduce suicidality. The rapid acting nature of ketamine further supports its use in treating suicidality and potentially preventing the completion of suicide. Evidence for the effectiveness of ketamine in other domains is weak, primarily due to a lack of robust studies specifically designed to assess these domains as primary outcomes. Future studies should scrutinize the effects of ketamine on specific domains of depression to optimize its implementation.

Functional connectivity differences in the amygdala are related to the antidepressant efficacy of ketamine in patients with anxious depression

BACKGROUND

The antidepressant effects of ketamine in patients with anxious depression (AD) remain unclear. Functional connectivity (FC) differences in the amygdala have been linked to depression improvement after ketamine treatment in depressed patients, but their role in AD patients is uncertain. We investigated the correlation between depression improvement after ketamine treatment and amygdala FC in AD patients.

METHODS

Thirty-one AD patients and 18 non-anxious depression (NAD) patients received six intravenous ketamine infusions (0.5 mg/kg) over two weeks. AD patients were further divided into responders (defined as a ≥50% MADRS total score reduction on day 13) and non-responders. The FC of the amygdala subregions, including the laterobasal amygdala (LBA), centromedial amygdala (CMA), and superficial amygdala, were compared between the groups. Receiver operating characteristic curves were used to predict treatment response after ketamine infusions.

RESULTS

The baseline FC difference in the left LBA and the left precuneus between responders and non-responders among AD patients was found to be associated with depression improvement and was a significant predictor of treatment response to ketamine. A marked reduction in baseline LBA-precuneus FC after ketamine infusion was observed in responders. Unlike in patients with NAD, a lower right CMA-right middle temporal gyrus FC was found in AD patients.

LIMITATIONS

The sample size is rather small.

CONCLUSIONS

Our findings may suggest that amygdala FC is a significant predictor of treatment response to ketamine infusions in patients with AD. Further studies exploring the potential antidepressant mechanisms of ketamine may aid in the treatment of AD patients.

Pharmacological targeting of cognitive impairment in depression: recent developments and challenges in human clinical research

Impaired cognition is often overlooked in the clinical management of depression, despite its association with poor psychosocial functioning and reduced clinical engagement. There is an outstanding need for new treatments to address this unmet clinical need, highlighted by our consultations with individuals with lived experience of depression. Here we consider the evidence to support different pharmacological approaches for the treatment of impaired cognition in individuals with depression, including treatments that influence primary neurotransmission directly as well as novel targets such as neurosteroid modulation. We also consider potential methodological challenges in establishing a strong evidence base in this area, including the need to disentangle direct effects of treatment on cognition from more generalised symptomatic improvement and the identification of sensitive, reliable and objective measures of cognition.

Ketamine treatment for refractory anxiety: A systematic review

There is a growing interest in the psychiatric properties of the dissociative anaesthetic ketamine, as single doses have been shown to have fast-acting mood-enhancing and anxiolytic effects, which persist for up to a week after the main psychoactive symptoms have diminished. Therefore, ketamine poses potential beneficial effects in patients with refractory anxiety disorders, where other conventional anxiolytics have been ineffective. Ketamine is a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) glutamate receptor, which underlies its induction of pain relief and anaesthesia. However, the role of NMDA receptors in anxiety reduction is still relatively unknown. To fill this paucity in the literature, this systematic review assesses the evidence that ketamine significantly reduces refractory anxiety and discusses to what extent this may be mediated by NMDA receptor antagonism and other receptors. We highlight the temporary nature of the anxiolytic effects and discuss the high discrepancy among the study designs regarding many fundamental factors such as administration routes, complementary treatments and other treatments.

Antianhedonic effects of serial intravenous subanaesthetic ketamine in anxious versus nonanxious depression

OBJECTIVES

Patents with anxious depression have poor treatment outcomes compared to their nonanxious counterparts. Ketamine has a rapid and robust antianhedonic effect, independent of depressive symptoms. The difference in the antianhedonic effect of ketamine between patients with anxious versus nonanxious depression remains unknown.

METHODS

One hundred thirty-five Chinese individuals with anxious depression (n = 92) and nonanxious depression (n = 43) received six intravenous infusions of ketamine (0.5 mg/kg). Post hoc analyses compared changes in anhedonic symptoms, as measured by the Montgomery-Åsberg Depression Rating Scale (MADRS), between patients with anxious depression (defined by a Hamilton Depression Rating Scale Anxiety-Somatization score ≥7) and nonanxious depression.

RESULTS

In this study, 68.1 % of patients were found to have anxious depression. Anxious depressed patients were associated with a relatively lower antianhedonic response (47.8 % versus 51.2 %, p > 0.05) and remission (17.4 % versus 27.9 %, p > 0.05) than their nonanxious counterparts. When compared to baseline, a significant reduction in anhedonic symptoms was observed from the first infusion to the last infusion and 2-week follow-up in both groups (all p < 0.05). A linear mixed model did not find a significant group main effect on the MADRS anhedonia subscale scores (F = 0.5, p = 0.46).

CONCLUSION

This preliminary study shows that repeated intravenous infusions of ketamine rapidly ameliorate anhedonic symptoms in individuals experiencing anxious depression, but these individuals displayed a weaker antianhedonic response to ketamine than nonanxious depressed patients.

Acute effects of ketamine and esketamine on cognition in healthy subjects: A meta-analysis

BACKGROUND

Impairment in cognition is frequently associated with acute ketamine administration. However, some questions remain unanswered as to which deficits are most prominent and what variables modulate these effects.

METHODS

A literature search yielded 56 experimental studies of acute ketamine administration that assessed cognition in 1041 healthy volunteers. A multivariate meta-analysis was performed, and effect sizes were estimated for eleven cognitive domains: attention, executive function, response inhibition, social cognition, speed of processing, verbal / language, verbal learning, verbal memory, visual learning & memory, visuospatial abilities, and working memory.

RESULTS

There were small-to-moderate impairments across all cognitive domains. Deficits in verbal learning / memory were most prominent, whereas response inhibition was the least affected. Meta-regression analysis revealed that the negative effects of ketamine on cognition are dependent on infusion dose and plasma level, but unaffected by enantiomer type, route of administration, sex or age. A publication bias was observed.

DISCUSSION

Acute ketamine broadly impairs cognition across all domains among healthy individuals. Verbal learning and memory figures most prominently in cognitive impairment elicited by acute ketamine administration.

Assessment of Objective and Subjective Cognitive Function in Patients With Treatment-Resistant Depression Undergoing Repeated Ketamine Infusions

BACKGROUND

Subanesthetic ketamine infusions can elicit rapid and sustained antidepressant effects, yet the potential cognitive impact of ketamine has not been thoroughly examined. This study measured changes in objective and subjective cognitive function following repeated ketamine treatment.

METHODS

Thirty-eight patients with treatment-resistant depression were administered cognitive assessments before and after undergoing 7 i.v. ketamine infusions (0.5 mg/kg over 40 minutes) within a clinical trial examining the efficacy of single and repeated administrations. Depression severity and perceived concentration were evaluated with the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Quick Inventory of Depressive Symptoms Self-Report.

RESULTS

Twenty-three participants (60.5%) responded after repeated infusions (≥50% decrease in MADRS total scores). We measured significant improvements in several cognitive domains, including attention, working memory, verbal, and visuospatial memory (effect sizes ranging from Cohen d = 0.37-0.79). Cognitive changes were attributed to reduction in depressive symptoms except for improvement in verbal memory, which remained significant after adjustment for change in MADRS total score (P = .029, η p2 = 0.13). Only responders reported improvement in subjective cognitive function with repeated ketamine administration (MADRS item 6, P < .001, d = 2.00; Quick Inventory of Depressive Symptoms Self-Report item 10, P < .001, d = 1.36).

CONCLUSION

A short course of repeated ketamine infusions did not impair neurocognitive function in patients with treatment-resistant depression. Further research is required to understand the potential mediating role of response and remission on improved cognitive function accompanying ketamine treatment as well as to examine longer-term safety outcomes. ClinicalTrials.gov identifier NCT01945047.

Neurocognitive effects of repeated ketamine infusions in comorbid posttraumatic stress disorder and major depressive disorder

BACKGROUND

The glutamate N-methyl-d-aspartate (NMDA) receptor antagonist ketamine rapidly ameliorates posttraumatic stress disorder (PTSD) and depression symptoms in individuals with comorbid PTSD and major depressive disorder (MDD). However, concerns over ketamine's potential neurocognitive side effects have yet to be assessed in this population. The current study investigated 1) changes in neurocognitive performance after a repeated ketamine dosing regimen and 2) baseline neurocognitive performance as a predictor of ketamine treatment effect.

METHOD

Veterans with comorbid PTSD and MDD (N = 15) received six infusions of 0.5 mg/kg ketamine over a 12-day period. Neurocognitive and clinical outcomes assessments occurred at baseline and within 7 days of infusion-series completion using the CogState battery.

RESULTS

Repeated ketamine infusions did not significantly worsen any measures of cognition. Rather, significant improvement was observed in working memory following completion of the infusion series. In addition, greater improvements in PTSD and MDD symptoms were associated with lower working memory, slower processing speed and faster set shifting at baseline. Lower verbal learning was also predictive of improvement in depression.

LIMITATIONS

This study applied an open-label design without a placebo control. As such, it is not known to what extent the correlations or improvement in neurocognitive performance may have occurred under placebo conditions.

CONCLUSION

This is the first study to examine the neurocognitive effects of repeated ketamine in participants with comorbid PTSD and MDD. Our findings suggest potential baseline neurocognitive predictors of ketamine response for comorbid PTSD and MDD symptoms.

A Systematic Review of Neurocognitive Effects of Subanesthetic Doses of Intravenous Ketamine in Major Depressive Disorder, Post-Traumatic Stress Disorder, and Healthy Population

BACKGROUND AND OBJECTIVE: Ketamine, a noncompetitive, high-affinity antagonist of the N-methyl-D-aspartate type glutamate receptor, has been investigated for its high efficacy and rapid antidepressant effect and, more recently, for its potential utility in post-traumatic stress disorder (PTSD). The proposal that ketamine's antidepressant and anti-suicidal mechanism may be in part due to its procognitive effect contrasts with the well-established decreased performance on spatial working memory and pattern recognition memory among long-term frequent users. We aimed to review the neurocognitive effects of subanesthetic doses of intravenous ketamine in pharmacological studies among healthy subjects and patients with PTSD or depression.

METHODS

We included studies in English, among healthy adults, or with PTSD or unipolar or bipolar depression where the primary or secondary cognitive outcomes were measured by means of validated neuropsychological test. We excluded studies that reported the use of ketamine only in combination with other drugs or psychotherapy, or studies investigating emotion-laden cognitive functions.

RESULTS

Ketamine administration among patients with depression and possibly with PTSD does not show significant impairment of cognitive functions in the short-term, in contrast with the immediate altered cognitive dysfunction found in healthy subjects. The potential procognitive effects of ketamine seem more pronounced in cognitive domains of executive function, which is in line with the putative molecular, cellular, and synaptic mechanisms of ketamine's therapeutic action.

CONCLUSIONS

The potential procognitive effect of ketamine deserves further exploration. Whether ketamine has transient or sustained neurocognitive benefits beyond its antidepressant effects is unknown. Improved cognition by ketamine might be used to facilitate psychotherapy interventions for PTSD and depression.

Ketamine and esketamine for crisis management in patients with depression: Why, whom, and how?

Currently, only a limited number of interventions can rapidly relieve depressive symptomatology in patients with major depressive disorder or bipolar disorder experiencing extreme distress. Such crises, especially when suicide attempt or ideation is involved, are a major risk factor of suicide. Ketamine, a N-methyl-d-aspartate glutamate receptor antagonist, and its enantiomer esketamine rapidly reduce depressive symptoms in depressed patients with current suicidal ideation. Recently, esketamine has been approved for use in patients with depression at risk of suicide and for psychiatric emergency by major medical agencies in the United States and Europe, whereas ketamine is increasingly used off-label. However, there is currently limited guidance on why, when, and how to use these drugs in patients with depression to treat a crisis. In this review article, we provide a succinct overview of the cellular and molecular mechanisms of action of ketamine and esketamine, and of the functional brain changes following their administration. We also summarize the major clinical studies on ketamine and esketamine efficacy in patients experiencing a crisis (generally, suicidal ideation), and propose a profile of patients who can benefit most from such drugs, on the basis of neurobiological and clinical observations. Finally, we describe the administration mode, the efficacy and tolerability profiles, the side effect management, possible concomitant treatments and the issue of deprescribing.

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.

(R,S)-ketamine and (2R,6R)-hydroxynorketamine differentially affect memory as a function of dosing frequency

A single subanesthetic infusion of ketamine can rapidly alleviate symptoms of treatment-resistant major depression. Since repeated administration is required to sustain symptom remission, it is important to characterize the potential untoward effects of prolonged ketamine exposure. While studies suggest that ketamine can alter cognitive function, it is unclear to what extent these effects are modulated by the frequency or chronicity of treatment. To test this, male and female adolescent (postnatal day [PD] 35) and adult (PD 60) BALB/c mice were treated for four consecutive weeks, either daily or thrice-weekly, with (R,S)-ketamine (30 mg/kg, intraperitoneal) or its biologically active metabolite, (2R,6R)-hydroxynorketamine (HNK; 30 mg/kg, intraperitoneal). Following drug cessation, memory performance was assessed in three operationally distinct tasks: (1) novel object recognition to assess explicit memory, (2) Y-maze to assess working memory, and (3) passive avoidance to assess implicit memory. While drug exposure did not influence working memory performance, thrice-weekly ketamine and daily (2R,6R)-HNK led to explicit memory impairment in novel object recognition independent of sex or age of exposure. Daily (2R,6R)-HNK impaired implicit memory in the passive-avoidance task whereas thrice-weekly (2R,6R)-HNK tended to improve it. These differential effects on explicit and implicit memory possibly reflect the unique mechanisms by which ketamine and (2R,6R)-HNK alter the functional integrity of neural circuits that subserve these distinct cognitive domains, a topic of clinical and mechanistic relevance to their antidepressant actions. Our findings also provide additional support for the importance of dosing frequency in establishing the cognitive effects of repeated ketamine exposure.

Neurocognitive Effects of Ketamine and Esketamine for Treatment-Resistant Major Depressive Disorder: A Systematic Review

LEARNING OBJECTIVE

After participating in this activity, learners should be better able to:• Analyze the effects of ketamine and esketamine on individuals with treatment-resistant depression.

INTRODUCTION

Cognitive impairment is commonly present in individuals with treatment-resistant depression, especially in attention, memory, and executive functions. These deficits are related to symptom severity, remission rates, and functional impairments during and after the acute phase of the disorder. Ketamine, an N-methyl-D-aspartate antagonist previously used as an anesthetic, brings promising antidepressant results. This study systematically reviews the neurocognitive effects of ketamine and esketamine in patients with treatment-resistant major depressive disorder.

METHODS

Systematic searches were conducted at Embase, PubMed, and PsycINFO using the terms depression, ketamine, and cognition. Title, abstract, and full-text reading were conducted independently by two of the authors (BSM and CSL). Risk of bias, study design, neuropsychological outcomes, and neuroimaging data were recorded.

RESULTS

From a total of 997 hits, 14 articles were included. One study reported cognitive impairment after ketamine treatment for processing speed and verbal memory. Five studies reported improvements in processing speed, verbal memory, visual memory, working memory, or cognitive flexibility. The esketamine study suggested no changes to performance. Lower attention, slower processing speed, and higher working memory are reported as predictors of antidepressant response. Brain areas for emotional and reward processing, including the amygdala, insula, and orbitofrontal cortex, show a normalizing tendency after ketamine.

CONCLUSIONS

Ketamine and esketamine do not seem to exert significant deleterious neurocognitive effects in the short or long term in individuals with treatment-resistant depression. Results suggest neuropsychological functions and brain areas commonly impaired in treatment-resistant depression may especially benefit from subanesthetic ketamine infusions. Key questions that remain unanswered are discussed.

Efficacy of ketamine for major depressive episodes at 2, 4, and 6-weeks post-treatment: A meta-analysis

RATIONALE

Major depressive episodes are severe mood episodes which occur both in major depressive disorder and bipolar I and II disorder. Major depressive episodes are characterized by debilitating symptoms that often persist and interfere with typical daily functioning. Various treatments exist for major depressive episodes; however, most primary pharmacologic treatments may take weeks to months to provide relief from depressive symptoms. Ketamine is a demonstrated treatment for major depressive episodes, as relief from depressive symptoms can occur rapidly following treatment.

OBJECTIVES

Prior meta-analyses have been conducted to analyze the effectiveness of ketamine for the treatment of major depressive episodes, but at the time of this writing, no meta-analysis had been conducted to observe ketamine treatment efficacy beyond 2 weeks.

METHODS

The present meta-analysis evaluated the efficacy of ketamine for the treatment of major depressive episodes; observations of depressive episode severity were analyzed at 2, 4, and 6-weeks post-treatment.

RESULTS

The present meta-analysis observed large effects at 2 weeks (g = -1.28), 4 weeks, (g = -1.28), and 6 weeks (g = -1.36) post-treatment.

CONCLUSIONS

The results from the present meta-analysis indicate that ketamine can be an effective pharmacologic intervention for major depressive episodes, with treatment effects lasting up to 6 weeks post-ketamine administration, which has many positive implications for treatment.

Neurocognitive performance of repeated versus single intravenous subanesthetic ketamine in treatment resistant depression

BACKGROUND

Ketamine demonstrated rapid antidepressant effects in treatment-resistant depression (TRD). However, evaluation of ketamine's neurocognitive effect in TRD is unclear. We aim to (1) characterize baseline neurocognitive performance as a predictor of the change in severity of depressive symptoms over time, and (2) investigate the association of six versus single intravenous (IV) ketamine and neurocognitive changes from baseline to the end of treatment.

METHODS

Subjects with TRD were randomized to receive either five IV midazolam followed by a single IV ketamine or six IV ketamine during a 12-day period. Depression symptom assessments occurred prior and 24 h after infusion days using the Montgomery-Åsberg Depression Rating Scale. Neurocognitive tasks were designed to test attention, memory, speed of processing, and set shifting using the CogState battery at baseline and at the end of treatment.

RESULTS

Better complex working memory at baseline predicted improvement in MADRS scores of ketamine (vs midazolam) after 5 infusions. Most, but not all, neurocognitive functions remained stable or improved after repeated or single ketamine. There was a greater differential effect of treatment on speed of processing, set shifting, and spatial working memory that favors subjects in the six ketamine group. These cognitive improvements from baseline to the end of treatment were robust when controlling for age and changes in depression severity.

CONCLUSION

The study suggests that six IV ketamine compared to single IV ketamine has a mood independent procognitive effect among TRD patients. Large scale studies are needed to confirm whether ketamine enhances cognitive function in TRD.

The Effects of Ketamine on Cognition in Treatment-Resistant Depression: A Systematic Review and Priority Avenues for Future Research

Replicated evidence has documented cognitive deficits in populations with treatment-resistant depression (TRD). Approximately 40 % of patients with MDD present with impairment of one or more cognitive domains. As such, there is an unmet need to discover treatments that have pro-cognitive effects in TRD patients. Ketamine has demonstrated efficacy as a rapid-onset intervention for the treatment of depression. The objective of the current review was to assess the effects of ketamine on cognition in TRD patients. We systematically searched PubMed, Google Scholar and PsycINFO between database inception to March 24th, 2020. We identified five studies that evaluated cognition in TRD populations following ketamine treatment. All studies included a 0.5 mg/kg subanesthetic intravenous (IV) administration of ketamine. One study found significant improvements in complex (p = .008) and simple (p = .027) working memory and one study found improvements in visual learning memory following IV ketamine infusions (p = .014). Improvements in speed of processing and verbal learning memory were observed in anxious TRD participants only. Importantly, a subanesthetic dose of IV ketamine does not worsen cognitive function.

The effectiveness of repeated intravenous ketamine on depressive symptoms, suicidal ideation and functional disability in adults with major depressive disorder and bipolar disorder: Results from the Canadian Rapid Treatment Center of Excellence

BACKGROUND

The effectiveness, tolerability, and safety of intravenous (IV) ketamine in adults with treatment resistant depression (TRD) receiving care in real-word settings is insufficiently characterized. Herein, results from a naturalistic, retrospective study are presented from a Canadian outpatient IV ketamine clinic.

METHODS

Adults (N = 213; M_age = 45) with Major Depressive Disorder or Bipolar Disorder, with a minimum of Stage 2 antidepressant resistance, received IV ketamine at a community-based multi-disciplinary clinic. The primary outcome measure was change from baseline to post-infusion 4 on the Quick Inventory for Depression Symptomatology-Self Report-16 (QIDS-SR₁₆; n = 190). Secondary measures included QIDS-SR₁₆-measured response and remission rates, changes from baseline to endpoint in Generalized Anxiety Disorder-7 Scale (GAD-7; n = 188) and the Sheehan Disability Scale (SDS; n = 168).

RESULTS

Significant improvement in total depressive symptoms severity (p < 0.0001) was observed after four infusions of IV ketamine 0.5-0.75 mg/kg. Moreover, the response rate (QIDS-SR₁₆ total score change ≥ 50%) was 27% and remission (QIDS-SR₁₆ total score ≤5) rate was 13%. Patients receiving IV ketamine exhibited anxiolytic effects (p < 0.0001,), improved overall psychosocial function (p < 0.0001), and reduced suicidal ideation (p < 0.0001). Compared to the baseline infusion, dissociation severity significantly reduced in subsequent infusions.

LIMITATIONS

This was a naturalistic, retrospective study, without a control group.

CONCLUSIONS

IV ketamine was safe, well-tolerated, and effective at improving depressive, anxiety, and functional impairment symptoms in a well-characterized cohort of adults with TRD.

Ketamine as an antidepressant: overview of its mechanisms of action and potential predictive biomarkers

Ketamine, a drug introduced in the 1960s as an anesthetic agent and still used for that purpose, has garnered marked interest over the past two decades as an emerging treatment for major depressive disorder. With increasing evidence of its efficacy in treatment-resistant depression and its potential anti-suicidal action, a great deal of investigation has been conducted on elucidating ketamine's effects on the brain. Of particular interest and therapeutic potential is the ability of ketamine to exert rapid antidepressant properties as early as several hours after administration. This is in stark contrast to the delayed effects observed with traditional antidepressants, often requiring several weeks of therapy for a clinical response. Furthermore, ketamine appears to have a unique mechanism of action involving glutamate modulation via actions at the N-methyl-D-aspartate (NMDA) and α -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, as well as downstream activation of brain-derived neurotrophic factor (BDNF) and mechanistic target of rapamycin (mTOR) signaling pathways to potentiate synaptic plasticity. This paper provides a brief overview of ketamine with regard to pharmacology/pharmacokinetics, toxicology, the current state of clinical trials on depression, postulated antidepressant mechanisms and potential biomarkers (biochemical, inflammatory, metabolic, neuroimaging sleep-related and cognitive) for predicting response to and/or monitoring of therapeutic outcome with ketamine.