Letter: Beyond Crisis, Prolonged Effectiveness of Ketamine in Adolescents with Treatment-Refractory Depression.

ObjectiveTo firstly examine the relationship between serum brain-derived neurotrophic factor (BDNF) levels and antidepressant response to ketamine as an anaesthesia in electroconvulsive therapy (ECT) in Chinese patients with treatment-refractory depression (TRD).MethodsThirty patients with TRD were enrolled and underwent eight ECT sessions with ketamine anaesthesia (0.8 mg/kg) alone. Depression severity, response and remission were evaluated using the 17-item Hamilton Depression Rating Scale (HAMD-17). Enzyme-linked immunosorbent assay (ELISA) was applied to examine serum BDNF levels in patients with TRD at baseline and after the second, fourth and eighth ECT sessions. Baseline serum samples were also collected for 30 healthy controls.ResultsNo significant differences were observed in serum BDNF levels between patients with TRD and healthy controls at baseline (p > 0.05). The remission rate was 76.7% (23/30) after the last ECT treatment, although all patients with TRD obtained antidepressant response criteria. Serum BDNF levels were not altered compared to baseline, even between remitters and nonremitters (all p > 0.05), despite the significant reduction in HAMD-17 and Brief Psychiatric Rating Scale (BPRS) scores after ECT with ketamine anaesthesia (all p < 0.05). The antidepressant effects of ECT with ketamine anaesthesia were not correlated with changes in serum BDNF levels (all p > 0.05).ConclusionThis preliminary study indicated that serum BDNF levels do not appear to be a reliable biomarker to determine the antidepressant effects of ketamine as an anaesthesia in ECT for patients with TRD. Further studies with larger sample sizes are warranted to confirm these findings.

Objectives: To first explore the role of plasma vascular endothelial growth factor (VEGF) concentrations in ketamine's antianhedonic effects, focusing on Chinese patients with treatment-refractory depression (TRD).Methods: Seventy-eight patients with treatment-refractory major depressive disorder (MDD) or bipolar disorder (BD) were treated with six ketamine infusions (0.5 mg/kg). Levels of anhedonia were measured using the Montgomery–Åsberg Depression Rating Scale (MADRS) anhedonia item at baseline, day 13 and 26. Plasma VEGF concentrations were examined at the same time points as the MADRS.Results: Despite a significant reduction in anhedonia symptoms in individuals with treatment-refractory MDD (n = 59) or BD (n = 19) after they received repeated-dose ketamine infusions (p < 0.05), no significant changes in plasma VEGF concentrations were found at day 13 when compared to baseline (p > 0.05). The alteration of plasma VEGF concentrations did not differ between antianhedonic responders and non-responders at days 13 and 26 (all ps > 0.05). Additionally, no significant correlations were observed between the antianhedonic response to ketamine and plasma VEGF concentrations (all ps > 0.05).Conclusion: This preliminary study suggests that the antianhedonic effects of ketamine are not mediated by VEGF.

(R,S)-Ketamine produces rapid, robust, and sustained antidepressant effects in major depressive disorder. Specifically, its pharmacological efficacy in treatment refractory depression is considered a major breakthrough in the field. However, the mechanism of action of ketamine's rapid effect remains to be determined. In order to identify pathways that are responsible for ketamine's effect, a targeted metabolomic approach was carried out using a double-blind, placebo-controlled crossover design, with infusion order randomized with medication-free patients with treatment-resistant major depressive disorder (29 subjects) and healthy controls (25 subjects). The metabolomic profile of these subjects was characterized at multiple time points, and a comprehensive analysis was investigated between the following: MDD and healthy controls, treatment and placebo in both groups and the corresponding response to ketamine treatment. Ketamine treatment resulted in a general increase in circulating sphingomyelins, levels which were not correlated with response. Ketamine response resulted in more pronounced effects in the kynurenine pathway and the arginine pathway at 4h post-infusion, where a larger decrease in circulating kynurenine levels and a larger increase in the bioavailability of arginine were observed in responders to ketamine treatment, suggesting possible mechanisms for response to ketamine treatment.

The N-methyl-D-aspartate (NMDA) glutamate receptor antagonist ketamine has demonstrated rapid antidepressant effects in patients with treatment-resistant depression (TRD). Despite the promise of a novel and urgently needed treatment for refractory depression, concerns regarding potential adverse neurocognitive effects of ketamine remain. Although extensive research has been conducted in healthy volunteers, there is a paucity of studies examining the neurocognitive effects of ketamine in depressed patients. Therefore, the aims of the current study were to characterize the relationship between baseline neurocognition and antidepressant response to ketamine, measure the acute impact of ketamine on neurocognition, and investigate the relationship between acute neurocognitive effects of ketamine and antidepressant response. Neurocognitive functioning was assessed in 25 patients with TRD using a comprehensive battery: estimated premorbid intelligence quotient (IQ), current IQ, and tests from the MATRICS Consensus Cognitive Battery (MCCB). A subset of the MCCB was repeated immediately following a 40-min intravenous infusion of ketamine (0.5mg/kg). Patients who responded to ketamine 24h following treatment had poorer baseline neurocognitive performance relative to nonresponders and, in particular, slower processing speed (F = 8.42; df = 23; p = 0.008). Ketamine was associated with selective impairments in memory recall, and the degree of cognitive change carried negative prognostic significance (e.g., negative cognitive effects immediately after ketamine predicted lower response rate at 24h; Fisher's exact test two-sided p = 0.027). Taken together, our findings suggest a potential baseline neurocognitive predictor of ketamine response and an inverse relationship between the cognitive effects of ketamine and antidepressant efficacy.

Is the antidepressant effect of ketamine separate from its psychotomimetic effect? A review of rodent models

Ketamine, an N-methyl-d-aspartate receptor antagonist, has been "repurposed" as a rapid-acting antidepressant for treatment-resistant depression (TRD). The s-enantiomer of ketamine, "esketamine," was FDA approved for TRD and depressive symptoms in adults with major depressive disorder with suicidal ideations/behaviors. Intravenous (IV) ketamine, although financially less expensive, is often not covered by insurance and intranasal (IN) esketamine, although covered by insurance can be expensive. There is a paucity of literature on efficacy data comparing subanesthetic IV ketamine and IN esketamine for TRD in a real-world scenario. Thus, we conducted this study comparing the efficacy and the number of treatments required to achieve remission/response with repeated use of subanesthetic IV ketamine/IN esketamine among TRD patients. This was an observational study where we included adults (≥18years) with TRD who provided consent and had received up to 6 IV ketamine infusions (0.5mg/kg, infused over 40minutes) or up to 8 intranasal (IN) esketamine (56/84mg) treatments for TRD at the Mayo Clinic Depression Center. Depression symptoms were measured utilizing the self-report 16-Item Quick Inventory of Depressive Symptomatology (QIDS-SR) scale before and 24hours after ketamine/esketamine treatment. Remission and response were defined as QIDS-SR 16 score ≤5 and ≥50% change in QIDS-SR 16, respectively. Continuous variables are reported as means±SD and categorical variables as counts and percentages. The Wilcoxon rank-sum test was used to compare continuous variables. Chi-square and Fisher's exact tests were used to compare categorical variables. The number of treatments to remission/response was calculated. Sixty-three adults with TRD, middle-aged (47.0±12.1 years), predominantly female (65%), of which 76% (n=48) and 24% (n=15) received IV ketamine and IN esketamine, respectively. Mean (SE) change in QIDS-SR 16 score was -8.7±0.7 (P<.001), a significant reduction (improvement) from baseline (mean±SD=17.6±3.7). Overall remission and response rates were 36.5% and 55.6%, respectively in the acute phase. Response (56.3% vs 53.3%) and remission rates (39.6% vs 26.7%) were similar among patients who received IV ketamine or IN esketamine, respectively (P>.05). The mean number of treatments received to achieve response (2.5±1.6 vs 4.6±2.1) and remission (2.4±1.3 vs 6.3±2.4) were significantly lower among patients who received IV ketamine compared to IN esketamine (P<.005). Most patients tolerated both treatments well. Intravenous ketamine and intranasal esketamine showed similar response/remission in TRD patients but the number of treatments required to achieve response/remission was significantly lower with IV ketamine compared to IN esketamine. These findings need to be investigated in a randomized control trial comparing these two treatment interventions. No funding.

Ketamine is a novel, rapid-acting antidepressant for treatment refractory depression (TRD); however, clinical durability is poor and treatment response trajectories vary. Little is known about which patient characteristics predict faster or more durable ketamine responses. Ketamine's antidepressant mechanism may involve modulation of glutamatergic signaling and long-term potentiation (LTP); these neuroplasticity pathways are also attenuated with older age. A retrospective analysis examining the impact of patient age on the speed and durability of ketamine's antidepressant effects in 49 veterans receiving serial intravenous ketamine infusions for TRD. The relationship between age and percent change in Beck Depression Inventory (BDI-II) scores was compared across six serial ketamine infusions (twice-weekly for 3weeks) using a linear-mixed model. A significant Age-X-Infusion number interaction (F = 3.01, p = .0274) indicated that the relationship between age and treatment response depended on infusion number. Follow-up tests showed that younger age significantly predicted greater clinical improvement at infusion #4 (t = 3.02, p = .004); this relationship was attenuated at infusion #5 (t = 1.95, p = .057) and was absent at infusion #6. Age was not a significant predictor of treatment durability, defined as percent change in BDI-II 3weeks following infusion #6. These data preliminarily suggest that younger age is associated with a faster response over six serial ketamine infusions; by infusion #6 and subsequent weeks of clinical follow-up, age no longer predicts ketamine's antidepressant activity. Age may mediate the speed but not the durability or total efficacy of ketamine treatment, suggesting that dissociable mechanisms may underlie differing aspects of ketamine's antidepressant activity.

Objective: Ketamine has been redeveloped as a rapid-acting antidepressant for treatment-resistant depression (TRD). There is a paucity of literature comparing subanesthetic intravenous (IV) ketamine and US Food and Drug Administration (FDA)-approved intranasal (IN) esketamine for TRD in real-world clinical settings. We compared the efficacy and time to achieve remission/response with repeated ketamine and esketamine.Methods: An observational study of adults with TRD received up to 6 IV ketamine (0.5 mg/kg over 40 minutes) or up to 8 IN esketamine (56- or 84-mg) treatments from August 17, 2017, to June 24, 2021. Depressive symptoms were measured utilizing the 16-item Quick Inventory of Depressive Symptomatology self-report (QIDS-SR) before and 24 hours after treatment. Cox proportional hazard models were used to evaluate associations between time to response ( ≥ 50% change in QIDS-SR score) and remission (QIDS-SR score ≤ 5).Results: Sixty-two adults (median age = 50 years, 65% female) received IV ketamine (76%, n = 47) or IN esketamine (24%, n = 15). Neither baseline-to-endpoint change in QIDS-SR score nor response/remission rates were significantly different between groups. Time to remission, defined as number of treatments (adjusting for age, body mass index [BMI], sex, and baseline QIDS-SR score), was faster for IV versus IN treatment (HR = 5.0, P = .02).Conclusions: Intravenous ketamine and intranasal esketamine showed similar rates of response and remission in TRD patients, but the number of treatments required to achieve remission was significantly lower with IV ketamine compared to IN esketamine. These findings need to be investigated in a randomized control trial comparing these two treatment interventions.

Ketamine, administered in subanesthetic doses, is gaining recognition as an off-label treatment for severe and even treatment-refractory depression. This article explores potential pharmacokinetic and pharmacodynamic drug interactions of relevance to the use of ketamine in depression. Sparse evidence suggests that ketamine will not induce clinically significant drug interactions except to the extent that these are predictable by its clinical actions. A small body of literature indicates that drugs that induce cytochrome P450 (CYP)2B6 and CYP3A4 will reduce exposure to ketamine and that drugs that inhibit these enzymes will increase exposure to ketamine. Common genetic polymorphisms of the CYP2B6 gene may also be associated with variations in the exposure to ketamine. However, the clinical implications of such variations in exposure have not been sufficiently studied. A very small number of reports and studies suggest that concurrent benzodiazepine medication may diminish the antidepressant benefits of ketamine. Likewise, a small body of literature suggests that drugs (such as lamotrigine) that inhibit glutamatergic signaling may reduce the adverse effects of ketamine; however, it is unknown whether these drugs also diminish the antidepressant effect. Data from clinical trials indicate that most conventional antidepressants can probably be combined with ketamine without compromising efficacy or increasing the adverse effect burden.​.

We aimed to develop population pharmacokinetic/pharmacodynamic (PK/PD) models that can effectively describe ketamine and norketamine PK/PD relationships for Montgomery–Åsberg Depression Rating Scale (MADRS) scores, blood pressure (BP), and heart rate (HR) following i.v., s.c., and i.m. ketamine administration in patients with treatment‐refractory depression. Ketamine PK/PD data were collected from 21 treatment‐refractory depressed participants who received ketamine (dose titration 0.1–0.5 mg/kg as single doses) by i.v., s.c., or i.m. administration. Model development used nonlinear mixed effect modeling. Ketamine and norketamine PK were best described using two‐compartment models with first‐order absorption after s.c. and i.m. administration. Estimated ketamine bioavailability after i.m. and s.c. was ~ 64% with indistinguishable first‐order absorption rate constants. Allometric scaling of body weight on all clearance and volumes of distribution improved the model fit. The delay in the concentration‐response relationship for MADRS scores was best described using a turnover model (turnover time ~ 42 hours), whereas for the BP and HR rates this was an immediate effect model. For all PD effects, ketamine alone was superior to models with norketamine concentration linked to an effect. No covariates were identified for PD effects. The estimated half‐maximal effective concentration from the MADRS score, BP, and HR were 0.44, 468, and 7,580 ng/mL, respectively. The integrated population models were able to effectively describe the PK/PD relationships for MADRS scores, BP, and HR after i.v., s.c., and i.m. ketamine administration. These findings allow for a deeper understanding of the complex relationships between route of ketamine administration and clinical response and safety.

Objectives Accumulating evidence suggests that the effects of ketamine administered intravenously at subanaesthetic doses on both anhedonic symptoms and suicidal ideation occur independently of depressive symptoms in major depressive disorder (MDD) and bipolar disorder (BD). This study sought to determine the relationship between anhedonia and suicidal ideation after serial ketamine infusions. Methods A total of 79 subjects with either treatment-refractory MDD (n = 60) or BD (n = 19) were included in a clinical ketamine study. The Montgomery–Åsberg Depression Rating Scale (MADRS) anhedonia factor and the first five items of the Scale for Suicidal Ideations (SSI-Part I) were used to assess anhedonia symptoms and suicidal ideation, respectively. Results At baseline, anhedonia, as measured by the MADRS, was not significantly associated with suicidal ideation or specific suicide-related ideation as measured by SSI-Part I (all p’s > 0.05). Only the ‘wish to die’ and ‘desire to make a suicide attempt’ items were positively associated with anhedonia at two weeks after the sixth ketamine infusion, which was independent of the reductions in depressive symptoms (all p’s < 0.05). Conclusion Anhedonia as measured by the MADRS appeared to not be positively related to suicidal ideation after serial ketamine infusions. KEY POINTS Serial ketamine (0.5 mg/kg) infusions have shown quick and dramatic antisuicidal and antianhedonic effects in patients with depression. The association between anhedonia and suicidal ideation after serial ketamine infusions is unclear. Anhedonia appeared to not be positively related to suicidal ideation after serial ketamine infusions.

Understanding the Efficacy and Mechanism of Action of a Dextromethorphan-Bupropion Combination: Where Does It Fit in the NMDA Versus mu-Opioid Story?

Major depressive disorder and bipolar depression are among the most prevalent and disabling mental disorders worldwide. Real-world effectiveness trials in major depressive disorder have underscored that most pharmacological options target monoamines, which are involved in a minority (15-20%) of synaptic contacts in the mammalian brain. Most synapses (∼50%) use the amino acid glutamate as their primary neurotransmitter, and preclinical models of depression have implicated aberrant glutamatergic neurotransmission for 25 years (1). More recently, the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist ketamine was shown to produce rapid and robust antidepressant effects in patients with treatment-resistant major depressive disorder and bipolar depression (2–7).

Anhedonia—which is defined as diminished pleasure from, or interest in, previously rewarding activities—is one of two cardinal symptoms of a major depressive episode. However, evidence suggests that standard treatments for depression do little to alleviate the symptoms of anhedonia and may cause reward blunting. Indeed, no therapeutics are currently approved for the treatment of anhedonia. Notably, over half of patients diagnosed with bipolar disorder experience significant levels of anhedonia during a depressive episode. Recent research into novel and rapid-acting therapeutics for depression, particularly the noncompetitive N-Methyl-D-aspartate receptor antagonist ketamine, has highlighted the role of the glutamatergic system in the treatment of depression; however, it is unknown whether ketamine specifically improves anhedonic symptoms. The present study used a randomized, placebo-controlled, double-blind crossover design to examine whether a single ketamine infusion could reduce anhedonia levels in 36 patients with treatment-resistant bipolar depression. The study also used positron emission tomography imaging in a subset of patients to explore the neurobiological mechanisms underpinning ketamine's anti-anhedonic effects. We found that ketamine rapidly reduced the levels of anhedonia. Furthermore, this reduction occurred independently from reductions in general depressive symptoms. Anti-anhedonic effects were specifically related to increased glucose metabolism in the dorsal anterior cingulate cortex and putamen. Our study emphasizes the importance of the glutamatergic system in treatment-refractory bipolar depression, particularly in the treatment of symptoms such as anhedonia.

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