Memantine augmentation in clozapine-refractory schizophrenia: a randomized, double-blind, placebo-controlled crossover study

Finding the Right Dose: NMDA Receptor-Modulating Treatments for Cognitive and Plasticity Deficits in Schizophrenia and the Role of Pharmacodynamic Target Engagement

Cognitive impairment associated with schizophrenia (CIAS) and related deficits in learning (plasticity) are among the leading causes of disability in schizophrenia. Despite this, there are no Food and Drug Administration-approved treatments for CIAS, and the development of treatments has been limited by numerous phase 2/3 failures of compounds that showed initial promise in small-scale studies. NMDA-type glutamate receptors (NMDARs) have been proposed to play an important role in schizophrenia; moreover, the NMDAR has a well-characterized role in cognition, learning, and neuroplasticity. We review previously published clinical trials in CIAS that focused on NMDAR modulator treatments, focusing on published and recent developments of the use of novel NMDAR-modulating treatments for CIAS both alone and combined with plasticity/learning paradigms to enhance learning. We use this discussion of previous studies to highlight the importance of incorporating pharmacodynamic target engagement biomarkers early in treatment development, which can help predict which compounds will succeed or fail in phase 3. A range of direct and indirect NMDAR modulators are covered, including D-serine, D-cycloserine, memantine, and glycine and first-generation glycine transport inhibitors (e.g., sarcosine and bitopertin), as well as recent positive studies of iclepertin, a novel glycine transport inhibitor, and luvadaxistat, a D-amino acid oxidase inhibitor that increases brain D-serine levels, and indirect noninvasive brain stimulation NMDAR-modulating treatments. Several examples of successful use of pharmacodynamic target engagement biomarkers for dose/drug discovery are emphasized, including the mismatch negativity, auditory steady state, and time-frequency event-related potential approaches.

Analysis of clinical studies on clozapine from 2012-2022

Clozapine has been considered the "gold standard" in the treatment of schizophrenia for many years. Clozapine has a superior effect, particularly in the treatment of negative symptoms and suicidal behaviour. However, due to its numerous adverse reactions, clozapine is mainly used for treatment-resistant schizophrenia. The aim of this paper is to analyze the results of clinical studies on clozapine from 2012-2022. PubMed was used as the database. Sixty-four studies were included and categorised by topic. The pharmacokinetic properties of clozapine tablets and a clozapine suspension solution did not differ markedly. Clozapine was superior to olanzapine and risperidone in reducing aggression and depression. A long-term study showed that metabolic parameters changed comparably with olanzapine and clozapine after 8 years. Risperidone and ziprasidone can be used as an alternative to clozapine. Scopolamine, atropine drops, and metoclopramide are effective in the treatment of clozapine-induced hypersalivation. Eight drugs, including liraglutide, exenatide, metformin, and orlistat, are potentially effective in the treatment of clozapine-induced weight gain. Ziprasidone, haloperidol, and aripiprazole showed a positive effect on symptoms when added to clozapine. No investigated drug was superior to clozapine for the treatment of schizophrenia. Ziprasidone and risperidone can also be used well for the treatment of schizophrenia. In the treatment of clozapine-induced hypersalivation and weight gain, some drugs proved to be effective.

Drugs with glutamate-based mechanisms of action in psychiatry

Psychopharmacotherapy of major psychiatric disorders is mostly based on drugs that modulate serotonergic, dopaminergic, or noradrenergic neurotransmission, either by inhibiting their reuptake or by acting as agonists or antagonists on specific monoamine receptors. The effectiveness of this approach is limited by a significant delay in the therapeutic mechanism and self-perpetuating growth of treatment resistance with a consecutive number of ineffective trials. A growing number of studies suggest that drugs targeting glutamate receptors offer an opportunity for rapid therapeutic effect that may overcome the limitations of monoaminergic drugs. In this article, we present a review of glutamate-modulating drugs, their mechanism of action, as well as preclinical and clinical studies of their efficacy in treating mental disorders. Observations of the rapid, robust, and long-lasting effects of ketamine and ketamine encourages further research on drugs targeting glutamatergic transmission. A growing number of studies support the use of memantine and minocycline in major depressive disorder and schizophrenia. Amantadine, zinc, and Crocus sativus extracts yield the potential to ameliorate depressive symptoms in patients with affective disorders. Drugs with mechanisms of action based on glutamate constitute a promising pharmacological group in the treatment of mental disorders that do not respond to standard methods of therapy. However, further research is needed on their efficacy, safety, dosage, interactions, and side effects, to determine their optimal clinical use.

Pharmacological Treatments of Negative Symptoms in Schizophrenia-An Update

Schizophrenia is a chronic psychotic disorder comprising positive symptoms, negative symptoms, and cognitive deficits. Negative symptoms are associated with stigma, worse functional outcomes, and a significant deterioration in quality of life. Clinical diagnosis is challenging despite its significance, and current treatments offer little improvement in the burden of negative symptoms. This article reviews current pharmacological strategies for treating negative symptoms. Dopaminergic, glutamatergic, serotonergic, noradrenergic, cholinergic, anti-inflammatory compounds, hormones, and psychostimulants are explored. Finally, we review pharmacological global treatment guidelines for negative symptoms. In general, switching to a second-generation antipsychotic seems to be most often recommended for patients with schizophrenia on first-generation antipsychotics, and an add-on antidepressant is considered when depression is also present. However, the treatment of negative symptoms remains an unmet need. Future, larger clinical studies and meta-analyses are needed to establish effective pharmacological agents for the effective treatment of negative symptoms.

Pharmacological management of neurocognitive impairment in schizophrenia: A narrative review

BACKGROUND

Cognitive impairment are among the core features of schizophrenia, experienced by up to 75% of patients. Available treatment options for schizophrenia including dopamine antagonists and traditional antipsychotic medications have not been shown to confer significant benefits on cognitive deficits. Contrary to the focus on management of positive symptoms in schizophrenia, cognitive abilities are main predictor of independent living skills, functional abilities, employment, engagement in relapse prevention, and patients' subjective sense of well-being and quality of life. This review aims to provide a summary of recent literature on pharmacological options for the treatment of cognitive deficits in schizophrenia.

METHODS

We conducted a literature search of studies from 2011 to 2021 across four electronic databases including PubMed, PsycInfo, MEDLINE, and Embase. Human studies using a pharmacological treatment for cognitive impairment in schizophrenia were included.

RESULTS

Fifty-eight eligible publications, representing 11 pharmacological classes, were included in this review. Major limitations involved small sample size, methodological limitations as well as heterogeneity of participants and outcome measures.

CONCLUSIONS

Overall evidence remains inconclusive for any pharmacological classes studied for the treatment of cognitive deficits in schizophrenia. Methodological limitations in a majority of the studies rendered their findings preliminary. We further discuss possible explanations for these findings that could guide future research.

Comprehensive evaluation of 45 augmentation drugs for schizophrenia: a network meta-analysis

Background

Antipsychotics are the gold standard treatment for schizophrenia, but many patients who receive treatment experience persistent symptoms. The aim of this network meta-analysis was to determine the efficacy of augmentation drugs for the treatment of schizophrenia.

Methods

In accordance with the PRISMA statement, the PubMed, Web of Science, Google Scholar, CENTRAL, clinical trial and EUDRACT databases were searched from inception to May 15th, 2023. To ensure the robustness of the results, only double-blind randomised controlled trials with a low risk of bias (measured by the Risk Of Bias v2 (ROB2) tool) were included. The studies were categorised according to the background regimen: participants were treated with risperidone, mixed antipsychotics or clozapine. A Bayesian network meta-analysis was conducted using a random effects model. PROSPERO register: CRD42023420964.

Findings

A total of 44 trials (comprising 45 augmentation drugs and 3358 participants) were included in the analysis. One-third of the drugs (16 drugs) demonstrated significant efficacy vs. placebo for at least one outcome. The most notable effect sizes (ESs) were observed for the use of tropisetron (standard mean difference: -0.83 [95% interval confidence -1.12 to -0.55]), memantine (-0.50 [-0.66 to -0.32]) and minocycline (-0.56 [-0.72 to -0.39]) to treat negative symptoms among patients treated with risperidone (moderate-to-high ESs). Studies involving mixed antipsychotics yielded lower ESs (small-to-moderate). Sodium benzoate (-0.41 [-0.60 to -0.21]) and memantine (-0.23 [-0.36 to -0.11]) were found have significant effects on positive symptoms, while memantine demonstrated efficacy for negative symptoms (-0.32 [-0.45 to -0.19]) and general psychopathology (-0.32 [-0.44 to -0.20]). Studies focusing exclusively on patients treated with clozapine revealed that duloxetine produced the best results (negative symptoms: -1.12 [-1.35 to -0.91]). Sodium benzoate was the only augmentation drug that demonstrated efficacy in relieving persistent positive symptoms (-0.32 [-0.59 to -0.08]) among patients treated with clozapine. Treatment with clozapine in combination with antipsychotics yielded small-to-moderate ESs.

Interpretation

The GRADE framework indicated that the quality of the evidence among the included studies was moderate, primarily due to the limited number of randomised controlled trials with a low risk of bias. Important drugs did not appear in these results due to insufficient low-risk-of-bias data for these medications. These results highlight new pathways for treating schizophrenia that should be incorporated into future guidelines after further validation.

Funding

No funding.

Higher orexin-A levels are associated with treatment response to clozapine in patients with schizophrenia: A cross-sectional study

BACKGROUND

Clozapine is the primary antipsychotic (APD) for treatment-resistant schizophrenia (TRS). However, only 40% of patients with TRS respond to clozapine, constituting a subgroup of clozapine-resistant patients. Recently, the neuropeptide orexin-A was shown to be involved in the pathophysiology of schizophrenia. This study evaluated the association of orexin-A levels with the clozapine response in patients with TRS.

METHODS

We recruited 199 patients with schizophrenia, including 37 APD-free and 162 clozapine-treated patients. Clozapine-treated patients were divided into clozapine-responsive (n = 100) and clozapine-resistant (n = 62) groups based on whether they had achieved psychotic remission defined by the 18-item Brief Psychiatric Rating Scale (BPRS-18). We compared blood orexin-A levels among the three groups and performed regression analysis to determine the association of orexin-A level with treatment response in clozapine-treated patients. We also explored the correlation between orexin-A levels and cognitive function, assessed using the CogState Schizophrenia Battery.

RESULTS

Clozapine-responsive patients had higher orexin-A levels than clozapine-resistant and APD-free patients. Orexin-A level was the only factor significantly associated with treatment response after adjustment. Orexin-A levels were negatively correlated with BPRS-18 full scale and positive, negative, and general symptoms subscale scores. We also observed a positive correlation between orexin-A levels and verbal memory, visual learning and memory, and working memory function.

CONCLUSIONS

This cross-sectional study showed that higher levels of orexin-A are associated with treatment response to clozapine in patients with TRS. Future prospective studies examining changes in orexin-A level following clozapine treatment and the potential benefit of augmenting orexin-A signaling are warranted.

Delirium due to Trousseau syndrome treated with memantine and perospirone: A case report

Background

Trousseau syndrome is a hypercoagulability syndrome associated with cancer. It is known that delirium occasionally occurs after the onset of Trousseau syndrome. However, there have been no detailed reports about treatment for psychiatric symptoms of delirium associated with Trousseau syndrome.

Case Presentation

A 61-year-old man with lung cancer was hospitalized due to Trousseau syndrome. Delirium occurred after hospitalization and psychiatric symptoms worsened. Although haloperidol, risperidone, and chlorpromazine were used, severe insomnia persisted. After memantine (5 mg/day) was used with perospirone, the patient's psychiatric symptoms gradually decreased; he could sleep for 4-5 h at night. Due to psychiatric improvement, he was able to return home and resume immunotherapy for lung cancer as scheduled.

Conclusion

We report the first case of Trousseau syndrome delirium treated by memantine used with perospirone. Although further studies are needed, memantine and perospirone might be candidates for the management of psychiatric symptoms associated with Trousseau syndrome.

Novel pharmacotherapy targeting the positive symptoms of schizophrenia

INTRODUCTION

The severity of positive symptoms in schizophrenia is associated with poor prognosis. About one-third of schizophrenia patients partially respond to treatment with available antipsychotics. The purpose of the present manuscript is to provide an updated overview of novel pharmacotherapy targeting positive symptoms in schizophrenia.

AREAS COVERED

A comprehensive research on the main database sources (PubMed, PsychINFO, Isi Web of Knowledge, MEDLINE, and EMBASE) was performed to obtain original articles published till 31st January 2023 about new pharmacological strategies for the treatment of positive symptoms in schizophrenia.

EXPERT OPINION

The most promising compounds include: lamotrigine, pro-cognitive-compounds (donepezil - in the short term, idazoxan and piracetam) and drugs acting partially or totally outside the Central Nervous System (CNS) (anti-inflammatory drugs: celecoxib, methotrexate; cardiovascular compounds: L-theanine, mononitrate isosorbide, propentofylline, sodium nitroprusside; metabolic regulators: diazoxide, allopurinol; others: bexarotene, raloxifene [in women]). The effectiveness of the latter compounds indicates that other biological systems, such as immunity or metabolism can be object of future research to identify pharmacological targets for positive symptoms of schizophrenia. Mirtazapine could be useful for treating negative symptoms without increasing the risk of a worsening of delusions/hallucinations. Nevertheless, the lack of replication of studies prevents to draw definitive conclusions and future studies are needed to confirm the findings presented in this overview.

Negative symptoms in schizophrenia: Newly emerging measurements, pathways, and treatments

The negative symptoms of schizophrenia, which often appear earlier than any other symptom, are prominent and clinically relevant in the majority of patients. As a result, interest in their treatment has increased. Patients who exhibit significant negative symptoms have worse functional outcomes than those without, resulting in impairments in occupational, household, and recreational functioning, as well as difficulties in relationships. Yet treatment with currently available medications does not lead to any significant improvements in this core component of schizophrenia. An increased understanding of the pathophysiology underlying negative symptoms and the discovery of novel treatments that do not directly target dopamine offer the potential to develop therapies that may reduce negative symptoms and increase quality of life for patients. The current article will discuss the impact of negative symptoms, outline current measurement tools for the assessment of negative symptoms, and examine how these measures may be improved. Insights into the neural circuitry underlying negative symptoms will be discussed, and promising targets for the development of effective treatments for these symptoms will be identified. As more prospective, large-scale, randomized studies focus on the effects of treatments on negative symptoms, progress in this area is foreseeable. However, improvements in clinical assessment instruments, a better understanding of the underlying neural mechanisms, development of novel treatments with varied targets, and a greater focus on personalized treatment are all important to produce significant benefits for patients with negative symptoms of schizophrenia.

Unveiling the Enigma: Exploring Risk Factors and Mechanisms for Psychotic Symptoms in Alzheimer's Disease through Electronic Medical Records with Deep Learning Models

Around 50% of patients with Alzheimer's disease (AD) may experience psychotic symptoms after onset, resulting in a subtype of AD known as psychosis in AD (AD + P). This subtype is characterized by more rapid cognitive decline compared to AD patients without psychosis. Therefore, there is a great need to identify risk factors for the development of AD + P and explore potential treatment options. In this study, we enhanced our deep learning model, DeepBiomarker, to predict the onset of psychosis in AD utilizing data from electronic medical records (EMRs). The model demonstrated superior predictive capacity with an AUC (area under curve) of 0.907, significantly surpassing conventional risk prediction models. Utilizing a perturbation-based method, we identified key features from multiple medications, comorbidities, and abnormal laboratory tests, which notably influenced the prediction outcomes. Our findings demonstrated substantial agreement with existing studies, underscoring the vital role of metabolic syndrome, inflammation, and liver function pathways in AD + P. Importantly, the DeepBiomarker model not only offers a precise prediction of AD + P onset but also provides mechanistic understanding, potentially informing the development of innovative treatments. With additional validation, this approach could significantly contribute to early detection and prevention strategies for AD + P, thereby improving patient outcomes and quality of life.

Augmentation Therapies as Treatments for Coexisting Somatic Problems in Schizophrenia-A Systematic Review

The aim of this review is to appraise the data from available randomized clinical trials (RCT) regarding the possible combinations of neuroleptic and non-antipsychotic treatment which could enhance antipsychotic therapy efficacy whilst simultaneously addressing somatic symptoms in individuals with schizophrenia. A systematic search of the PubMed database up to February 2022 was conducted. Inclusion criteria: randomized controlled trials using augmentation therapy in chronic schizophrenia in adults, written in English, and only studies with psychometric assessments of schizophrenia were incorporated. Exclusion criteria: non-clinical, first episode of schizophrenia, patients on medication other than antipsychotics augmented, and not adjunctive therapy. Overall, 37 studies of 1931 patients with schizophrenia who received a combination of antipsychotic medication with other drugs were selected. A statistically significant reduction of negative and positive symptoms of schizophrenia, measured with the PANSS scale, when using a combination of antipsychotic treatment along with aspirin, simvastatin, N-acetylcysteine, or pioglitazone was found. A combination of antipsychotic medication with aspirin, simvastatin, N-acetylcysteine, or pioglitazone seems to be effective in the reduction of symptoms of schizophrenia in adults, but long-term studies are required to confirm this effect.

Augmentation strategies for clozapine resistance: a systematic review and meta-analysis

BACKGROUND

Several augmentation strategies have been used to improve symptomatology in patients not adequately responding to clozapine. Several randomised controlled trials (RCTs) have evaluated the efficacy of different strategies to augment clozapine. This systematic review and meta-analysis reviewed the available RCTs that have evaluated the clinical efficacy of various pharmacological agents, non-pharmacological strategies (occupational therapy, cognitive behaviour therapy), and somatic treatment [electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation, etc.)] as augmenting agents to clozapine.

METHODS

Data were extracted using standard procedures, and risk of bias was evaluated. Effect sizes were computed for the individual studies.

RESULTS

Forty-five clinical trials were evaluated. The pooled effect size for various antipsychotic medications was 0.103 (95% CI: 0.288-0.493, p < 0.001); when the effect size was evaluated for specific antipsychotics for which more than one trial was available, the effect size for risperidone was -0.27 and that for aripiprazole was 0.57. The effect size for lamotrigine was 0.145, and that for topiramate was 0.392. The effect size for ECT was 0.743 (CI: 0.094-1.392). Risk of bias was low (mean Jadad score - 3.93). Largest effect sizes were seen for mirtazapine (effect size of 5.265). Most of the studies can be considered underpowered and limited by small sample sizes.

CONCLUSIONS

To conclude, based on the findings of the present systematic review and meta-analysis, it can be said that compared to other treatment strategies, clozapine non-responsive patients respond maximum to mirtazapine followed by ECT.

Thirty years of research on negative symptoms of schizophrenia: A scientometric analysis of hotspots, bursts, and research trends

Research on negative symptoms of schizophrenia has received renewed interest since the 1980s. A scientometric analysis that objectively maps scientific knowledge, with changes in recent trends, is currently lacking. We searched the Web of Science Core Collection (WOSCC) on December 17, 2021 using relevant keywords. R-bibliometrix and CiteSpace were used to perform the analysis. We retrieved 27,568 references published between 1966 and 2022. An exponential rise in scientific interest was observed, with an average annual growth rate in publications of 16.56% from 1990 to 2010. The co-cited reference network that was retrieved presented 24 different clusters with a well-structured network (Q=0.7921; S=0.9016). Two distinct major research trends were identified: research on the conceptualization and treatment of negative symptoms. The latest trends in research on negative symptoms include evidence synthesis, nonpharmacological treatments, and computational psychiatry. Scientometric analyses provide a useful summary of changes in negative symptom research across time by identifying intellectual turning point papers and emerging trends. These results will be informative for systematic reviews, meta-analyses, and generating novel hypotheses.

Glutamatergic dysfunction in Schizophrenia

The NMDA-R hypofunction model of schizophrenia started with the clinical observation of the precipitation of psychotic symptoms in patients with schizophrenia exposed to PCP or ketamine. Healthy volunteers exposed to acute low doses of ketamine experienced mild psychosis but also negative and cognitive type symptoms reminiscent of the full clinical picture of schizophrenia. In rodents, acute systemic ketamine resulted in a paradoxical increase in extracellular frontal glutamate as well as of dopamine. Similar increase in prefrontal glutamate was documented with acute ketamine in healthy volunteers with 1H-MRS. Furthermore, sub-chronic low dose PCP lead to reductions in frontal dendritic tree density in rodents. In post-mortem ultrastructural studies in schizophrenia, a broad reduction in dendritic complexity and somal volume of pyramidal cells has been repeatedly described. This most likely accounts for the broad, subtle progressive cortical thinning described with MRI in- vivo. Additionally, prefrontal reductions in the obligatory GluN1 subunit of the NMDA-R has been repeatedly found in post-mortem tissue. The vast 1H-MRS literature in schizophrenia has documented trait-like small increases in glutamate concentrations in striatum very early in the illness, before antipsychotic treatment (the same structure where increased pre-synaptic release of dopamine has been reported with PET). The more recent genetic literature has reliably detected very small risk effects for common variants involving several glutamate-related genes. The pharmacological literature has followed two main tracks, directly informed by the NMDA-R hypo model: agonism at the glycine site (as mostly add-on studies targeting negative and cognitive symptoms); and pre-synaptic modulation of glutamatergic release (as single agents for acute psychosis). Unfortunately, both approaches have failed so far. There is little doubt that brain glutamatergic abnormalities are present in schizophrenia and that some of these are related to the etiology of the illness. The genetic literature directly supports a non- specific etiological role for glutamatergic dysfunction. Whether NMDA-R hypofunction as a specific mechanism accounts for any important component of the illness is still not evident. However, a glutamatergic model still has heuristic value to guide future research in schizophrenia. New tools to jointly examine brain glutamatergic, GABA-ergic and dopaminergic systems in-vivo, early in the illness, may lay the ground for a next generation of clinical trials that go beyond dopamine D2 blockade.

A narrative review of treatment interventions to improve cognitive performance in schizophrenia, with an emphasis on at-risk and early course stages

Cognitive dysfunction is a core feature of schizophrenia (SCZ), which unfavorably affects SCZ patients' daily functioning and overall clinical outcome. An increasing body of evidence has shown that cognitive deficits are present not only at the beginning of the illness but also several years before the onset of psychosis. Nonetheless, the majority of treatment interventions targeting cognitive dysfunction in SCZ, using both pharmacological and nonpharmacological approaches, have focused on chronic patients rather than individuals at high risk or in the early stages of the disease. In this article, we provide a narrative review of cognitive interventions in SCZ patients, with a particular focus on pre-emptive interventions in at-risk/early course individuals when available. Furthermore, we discuss current challenges for these pre-emptive treatment interventions and provide some suggestions on how future work may ameliorate cognitive dysfunction in these individuals.

MDMA for the Treatment of Negative Symptoms in Schizophrenia

The profound economic burden of schizophrenia is due, in part, to the negative symptoms of the disease, which can severely limit daily functioning. There is much debate in the field regarding their measurement and classification and there are no FDA-approved treatments for negative symptoms despite an abundance of research. 3,4-Methylenedioxy methamphetamine (MDMA) is a schedule I substance that has emerged as a novel therapeutic given its ability to enhance social interactions, generate empathy, and induce a state of metaplasticity in the brain. This review provides a rationale for the use of MDMA in the treatment of negative symptoms by reviewing the literature on negative symptoms, their treatment, MDMA, and MDMA-assisted therapy. It reviews recent evidence that supports the safe and potentially effective use of MDMA to treat negative symptoms and concludes with considerations regarding safety and possible mechanisms of action.

Memantine for the Treatment of Behavioral Disturbance in Unspecified Major Neurocognitive Disorder

In this case report, we aimed to examine how the use of memantine in an elderly gentleman with unspecified major neurocognitive disorder (NCD) led to significant clinical improvement in his behavioral disturbances. After presenting to the psychiatric ward due to aggressive behavior at his assisted living facility, the patient continued to exhibit numerous disruptive and confrontational behaviors while hospitalized. Memantine was started at 5 mg daily with gradual titration up to 10 mg twice daily over the course of four weeks, with marked improvement in behavior as well as an increase in Montreal Cognitive Assessment (MoCA) score by five points after seven weeks of treatment. Given our experience and the safety profile of memantine, we conclude that memantine may have a role in the treatment of behavioral disturbances in patients with unspecified major NCD, though further research will be necessary to define this role.

Characteristics and definitions of ultra-treatment-resistant schizophrenia - A systematic review and meta-analysis

OBJECTIVE

The aim of this systematic review and meta-analysis was to characterize ultra-treatment-resistant Schizophrenia also known as clozapine-resistant schizophrenia (CRS) patients across clozapine combination and augmentation trials through demographic and clinical baseline data. Furthermore, we investigated the variability and consistency in CRS definitions between studies.

METHODS

Systematic searches of articles indexed in PubMed, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL) and PsycINFO were conducted in March 2020. 1541 randomized and non-randomized clinical trials investigating pharmacological and non-pharmacological clozapine add-on strategies were screened and a total of 71 studies were included. The primary outcome was the overall symptom score at baseline, measured with Positive and Negative Syndrome Scale (PANSS) total or Brief Psychiatric Rating Scale (BPRS) total scores.

RESULTS

Data from 2731 patients were extracted. Patients were overall moderately ill with a mean PANSS total score at baseline of 79.16 (±7.52), a mean duration of illness of 14.64 (±4.14) years with a mean clozapine dose of 436.94 (±87.47) mg/day. Illness severity data were relatively homogenous among patients independently of the augmentation strategy involved, although stark geographical differences were found. Overall, studies showed a large heterogeneity of CRS definitions and insufficient guidelines implementation.

CONCLUSIONS

This first meta-analysis characterizing CRS patients and comparing CRS definitions revealed a lack of consistent implementation of a CRS definition from guidelines into clinical trials, compromising the replicability of the results and their applicability in clinical practice. We offer a new score modeled on a best practice definition to help future trials increase their reliability.

Meta-analysis of cognitive functioning in patients with psychotic disorders and obsessive-compulsive symptoms

Obsessive-compulsive symptoms (OCS) in psychotic disorders are associated with unfavorable outcomes, whether this extends to cognitive function remains unclear. We conducted meta-analyses on several cognitive domains to investigate overall group differences between patients with a psychotic disorder and co-occurring OCS (OCS +) and those without OCS (OCS-). We used meta-regression to assess possible confounding effects. No overall associations between OCS + and OCS- in any of the 17 investigated cognitive domains were found. We predominantly found large heterogeneity in effect size and direction among studies. Post-hoc analyses of processing speed tasks not purely based on reaction-time showed worse performance in the OCS + group with a small effect size (SMD = - 0.190; p = 0.029). Meta-regression revealed advanced age was significantly correlated with worse performance of the OCS + group in processing speed (R² = 0.7), working memory (R² = 0.11), cognitive inhibition (R² = 0.59), and cognitive flexibility (R² = 0.34). Patients fulfilling the criteria for an obsessive-compulsive disorder showed less impairment in cognitive inhibition compared to the OCS + group (R² = 0.63). Overall, comorbid OCS were not associated with cognitive impairment. However, large heterogeneity between studies highlights the complex nature of factors influencing cognition in people with psychotic disorder and comorbid OCS and warrants further research into possible moderating factors.

In Silico Molecular Docking Analysis of Potential Anti-Alzheimer's Compounds Present in Chloroform Extract of Carissa carandas Leaf Using Gas Chromatography MS/MS

Background: The current treatment of Alzheimer's disease (AD) is far from adequate. AD can be treated by inhibiting either β-amyloid protein deposition or acetylcholinesterase enzyme activity. Many treatments for AD are directed at these 2 targets. In the present study, the phytoconstituents of Carissa carandas chloroform leaf extract were identified by gas chromatography-MS/MS analysis, and in silico molecular docking studies were performed to evaluate their potential against AD. Objectives: The present study aimed to identify the possible anti-Alzheimer's activity of novel phytoconstituents isolated from C carandas. Methods: The powdered leafy material was subjected to successive Soxhlet extraction using 3 different solvents: n-hexane, chloroform, and methanol. The chloroform extract was subjected to gas chromatography-MS/MS analysis, and the observed chromatogram revealed the presence of 48 chemical constituents. Among them, 42 new phytoconstituents are reported in this plant for the first time. The gas chromatography-MS/MS-identified phytoconstituents were evaluated by iGEMDOCK software against AD targets of β-amyloid fibril (protein data bank ID: 2LMN) and recombinant human acetylcholinesterase (protein data bank ID: 3LII) ligands, and their anti-AD potential were compared with those of known inhibitors of galantamine and curcumin. Results: On the basis of results from both docking assays, the 5 compounds with the highest docking energy were further analyzed using in silico admetSAR web portal modeling for the evaluation of parameters such as intestinal absorption, blood-brain barrier permeation, carcinogenicity, and acute oral toxicity. Conclusions: The chloroform leaf extract of C carandas was found to contain constituents that have affinities for the 2 targets tested; that is, amyloid β and acetylcholinesterase. The best docking scores were found for 7 compounds: 1-heneicosanol; N-nonadecanol-1; cholesta-4,6-dien-3-ol, (3beta); di-n-octyl phthalate; 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione; 6-undecyl-5,6-dihydro-2H-pyran-2-one, and phenol, 2,4-di-t-butyl-6-nitro compounds, and these compounds were therefore suggested to be promising anti-AD lead compounds. Further, the target leads were subjected to ligplot analysis for their 2-dimensional representation of hydrogen bonding and hydrophobic interactions. Thus, the results obtained from the in silico study of C carandas leaf extract using these computational approaches indicate the presence of phytoconstituents that have affinities for the selected 2 targets of AD. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX).

Clozapine: An Updated Overview of Pharmacogenetic Biomarkers, Risks, and Safety-Particularities in the Context of COVID-19

BACKGROUND

clozapine (CLZ) use is precarious due to its neurological, cardiovascular, and hematological side effects; however, it is the gold standard in therapy-resistant schizophrenia (TRS) in adults and is underused.

OBJECTIVE

to examine the most recent CLZ data on (a) side effects concerning (b) recent pharmacological mechanisms, (c) therapy benefits, and (d) the particularities of the COVID-19 pandemic.

DATA SOURCES

a search was performed in two databases (PubMed and Web of Science) using the specific keywords "clozapine" and "schizophrenia", "side effects", "agranulocytosis", "TRS", or "bipolar affective disorder (BAF)" for the last ten years.

STUDY ELIGIBILITY CRITERIA

clinical trials on adults with acute symptoms of schizophrenia or related disorders.

RESULTS

we selected 37 studies, randomized controlled trials (RCTs), and clinical case series (CCS), centered on six main topics in the search area: (a) CLZ in schizophrenia, (b) CLZ in bipolar disorder, (c) side effects during the clozapine therapy, (d) CLZ in pregnancy, (e) CLZ in early-onset schizophrenia, and (f) CLZ therapy and COVID-19 infection.

LIMITATIONS

we considered RCTs and CCS from two databases, limited to the search topics. Conclusions and implications of key findings: (a) clozapine doses should be personalized for each patient based on pharmacogenetics testing when available; the genetic vulnerability postulates predictors of adverse reactions' severity; patients with a lower genetic risk could have less frequent hematological monitoring; (b) a CLZ-associated risk of pulmonary embolism imposes prophylactic measures for venous thromboembolism; (c) convulsive episodes are not an indication for stopping treatment; the plasma concentration of clozapine is a better side effect predictor than the dosage; (d) COVID-19 infection may enhance clozapine toxicity, generating an increased risk of pneumonia. Therapy must be continued with the proper monitoring of the white blood count, and the clozapine dose decreased by half until three days after the fever breaks; psychiatrists and healthcare providers must act together.

Is Memantine Effective as an NMDA-Receptor Antagonist in Adjunctive Therapy for Schizophrenia?

Memantine, an n-methyl-d-aspartate (NMDA) receptor antagonist approved for treating Alzheimer's disease, has a good safety profile and is increasingly being studied for possible use in a variety of non-dementia psychiatric disorders. There is an abundance of basic and clinical data that support the hypothesis that NMDA receptor hypofunction contributes to the pathophysiology of schizophrenia. However, there are numerous randomized, double-blind, placebo-controlled clinical trials showing that add-on treatment with memantine improves negative and cognitive symptoms, particularly the negative symptoms of schizophrenia, indicating that memantine as adjunctive therapy in schizophrenia helps to ameliorate negative symptoms and cognitive deficits. It remains unclear why memantine does not show undesirable central nervous system (CNS) side effects in humans unlike other NMDA receptor antagonists, such as phencyclidine and ketamine. However, the answer could lie in the fact that it would appear that memantine works as a low-affinity, fast off-rate, voltage-dependent, and uncompetitive antagonist with preferential inhibition of extrasynaptic receptors. It is reasonable to assume that the effects of memantine as adjunctive therapy on negative symptoms and cognitive deficits in schizophrenia may derive primarily, if not totally, from its NMDA receptor antagonist activity at NMDA receptors including extrasynaptic receptors in the CNS.

Adjunctive Memantine Treatment of Schizophrenia: A Double-Blind, Randomized Placebo-Controlled Study

PURPOSE/BACKGROUND

This double-blind, placebo-controlled clinical trial was designed to assess the efficacy and safety of memantine augmentation to standard regimen of antipsychotic treatment on psychotic symptoms and cognitive function in individuals with chronic schizophrenia for 8 weeks.

METHODS/PROCEDURES

Forty stabilized individuals with chronic schizophrenia were randomized in a 1:1 ratio to memantine (20 mg/d) and control (placebo) groups, along with their antipsychotic regimen for 8 weeks. The efficacy of treatment was assessed by the Positive and Negative Syndrome Scale (PANSS) and Brief Assessment of Cognition Scale, and the safety was measured by the Abnormal Involuntary Movement Scale and Barnes Akathisia Rating Scale at baseline and at weeks 4 and 8.

FINDINGS/RESULTS

No significant differences were observed in demographic or clinical variables between both groups at baseline. During the study, all subscales and total scores of PANSS decreased significantly within both groups, except the subscale score in memantine, which was found to be positive. Reduction in general subscale and total scores of PANSS was significantly higher in the control group compared with the memantine group. All subscale scores of the Brief Assessment of Cognition Scale increased significantly only in the memantine group. The increase in the Verbal Memory, Working Memory, Verbal Fluency Letter, and Verbal Fluency Total subscale scores was significantly higher in the memantine group than in the control group. There was no significant difference in the Abnormal Involuntary Movement Scale and Barnes Akathisia Rating Scale scores between the 2 groups during the study.

IMPLICATIONS/CONCLUSIONS

This study showed that adjunctive memantine to antipsychotic regimen improved the verbal memory, learning, verbal letter fluency, and working memory without improvement on psychotic symptoms in individuals with chronic schizophrenia.

Pharmacological enrichment of polygenic risk for precision medicine in complex disorders

Individuals with complex disorders typically have a heritable burden of common variation that can be expressed as a polygenic risk score (PRS). While PRS has some predictive utility, it lacks the molecular specificity to be directly informative for clinical interventions. We therefore sought to develop a framework to quantify an individual’s common variant enrichment in clinically actionable systems responsive to existing drugs. This was achieved with a metric designated the pharmagenic enrichment score (PES), which we demonstrate for individual SNP profiles in a cohort of cases with schizophrenia. A large proportion of these had elevated PES in one or more of eight clinically actionable gene-sets enriched with schizophrenia associated common variation. Notable candidates targeting these pathways included vitamins, antioxidants, insulin modulating agents, and cholinergic drugs. Interestingly, elevated PES was also observed in individuals with otherwise low common variant burden. The biological saliency of PES profiles were observed directly through their impact on gene expression in a subset of the cohort with matched transcriptomic data, supporting our assertion that this gene-set orientated approach could integrate an individual’s common variant risk to inform personalised interventions, including drug repositioning, for complex disorders such as schizophrenia.

Clozapine augmentation strategies

Clozapine is established as the gold standard for antipsychotic treatment of patients suffering from treatment-resistant schizophrenia. Over virtually 3 decades, the level of inadequate response to clozapine was found to range from 40% to 60%. A heightened interest developed in the augmentation of clozapine to try to achieve response or maximize partial response. A large variety of drug groups have been investigated. This article focuses on the meta-analyses of these trials to discover reasonable evidence-based approaches to the management of patients not responding to clozapine.

Adjunctive memantine for major mental disorders: A systematic review and meta-analysis of randomized double-blind controlled trials

OBJECTIVE

As a non-competitive N-methyl-d-aspartate receptor antagonist, memantine has been used to treat major mental disorders including schizophrenia, bipolar disorder, and major depressive disorder (MDD). This meta-analysis systematically investigated the effectiveness and tolerability of adjunctive memantine for patients with schizophrenia, bipolar disorder, and MDD.

METHODS

Only randomized controlled trials (RCTs) were identified and included in the study. Data of the three disorders were separately synthesized using the RevMan 5.3 software.

RESULTS

Fifteen RCTs (n = 988) examining memantine (5-20 mg/day) as an adjunct treatment for schizophrenia (9 trials with 512 patients), bipolar disorder (3 trials with 319 patients), and MDD (3 trials with 157 patients) were analyzed. Memantine outperformed the comparator regarding total psychopathology with a standardized mean difference (SMD) of -0.56 [95% confidence interval (CI): -1.01, -0.11; I² = 76%, P = 0.01] and negative symptoms with an SMD of -0.71 (95% CI: -1.09, -0.33; I² = 74%, P = 0.0003) in schizophrenia, but no significant effects were found with regard to positive symptoms and general psychopathology in schizophrenia, or depressive and manic symptoms in bipolar disorder or depressive symptoms in MDD. Memantine outperformed the comparator in improving cognitive performance in schizophrenia with an SMD of 1.07 (95% CI: 0.53, 1.61; P < 0.0001, I² = 29%). No group differences were found in the rates of adverse drug reactions and discontinuation due to any reason in the three major mental disorders.

CONCLUSIONS

Memantine as an adjunct treatment appears to have significant efficacy in improving negative symptoms in schizophrenia. The efficacy and safety of adjunctive memantine for bipolar disorder or MDD needs to be further examined.

REVIEW REGISTRATION

PROSPERO: 42018099045.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Potential Role of Antipsychotic-Galantamine-Memantine Combination in the Treatment of Positive, Cognitive, and Negative Symptoms of Schizophrenia

Schizophrenia is, in part, a cognitive illness. There are no approved medications for cognitive impairments associated with schizophrenia (CIAS) and primary negative symptoms. Cholinergic and glutamatergic systems, alpha-7 nicotinic acetylcholine (α-7nACh) and N-methyl-D-aspartate (NMDA) receptors, kynurenic acid (KYNA), and mismatch negativity have been implicated in the pathophysiology of CIAS and negative symptoms. Galantamine is an acetylcholinesterase inhibitor that is also a positive allosteric modulator at the α4β2 and α7nACh receptors. Memantine is a noncompetitive NMDA receptor antagonist. Galantamine and memantine alone and in combination were effective for cognition in animals and people with Alzheimer's disease. The objective of this article is to critically dissect the published randomized controlled trials with galantamine and memantine for CIAS to highlight the efficacy signal. These studies may have failed to detect a clinically meaningful efficacy signal due to limitations, methodological issues, and possible medication nonadherence. There is evidence from a small open-label study that the galantamine-memantine combination may be effective for CIAS with kynurenine pathway metabolites as biomarkers to detect the severity of cognitive impairments. Given that there are no available treatments for cognitive impairments and primary negative symptoms in schizophrenia, testing of this "five-pronged strategy" (quintuple hypotheses: dopamine, nicotinic-cholinergic, glutamatergic/NMDA, GABA, and KYNA) is a "low-risk high-gain" approach that could be a major breakthrough in the field. The galantamine-memantine combination has the potential to treat positive, cognitive, and negative symptoms, and targeting the quintuple hypotheses concurrently may lead to a major scientific advancement - from antipsychotic treatment to antischizophrenia treatment.

Resistance is not futile: treatment-refractory schizophrenia - overview, evaluation and treatment

INTRODUCTION

Schizophrenia is a debilitating condition with three main symptom domains: positive, negative, and cognitive. Approximately one-third of persons with schizophrenia will fail to respond to treatment. Growing evidence suggests that treatment-resistant (refractory) schizophrenia (TRS) may be a distinct condition from treatment-respondent schizophrenia. There is limited evidence on effective treatments for TRS, and a lack of standardized diagnostic criteria for TRS has hampered research. Areas covered: A literature search was conducted using Pubmed.gov and the EMBASE literature database. The authors discuss the pragmatic definitions of TRS and review treatments consisting of antipsychotic monotherapy and augmentation strategies. Expert opinion: Currently available first-line antipsychotic medications are generally effective at treating the positive symptoms of schizophrenia, leaving residual negative and cognitive symptoms. Before diagnosing TRS, rule out any pharmacodynamic or pharmacokinetic failures. Most evidence supports clozapine as having the most efficacy for TRS. If clozapine is used, it should be optimized, and serum levels should be at least 350-420 ng/ml. If clozapine is unable to be tolerated, some evidence suggests olanzapine at dosages up to 40mg/day can be useful. Augmentation strategies have weak evidence. Tailoring treatment to the specific domain is the preferred approach, and the use of a structured assessment/outcome measure is encouraged.

Efficacy of different types of cognitive enhancers for patients with schizophrenia: a meta-analysis

Cognitive impairment is a core feature of schizophrenia, which is predictive for functional outcomes and is, therefore, a treatment target in itself. Yet, literature on efficacy of different pharmaco-therapeutic options is inconsistent. This quantitative review provides an overview of studies that investigated potential cognitive enhancers in schizophrenia. We included pharmacological agents, which target different neurotransmitter systems and evaluated their efficacy on overall cognitive functioning and seven separate cognitive domains. In total, 93 studies with 5630 patients were included. Cognitive enhancers, when combined across all different neurotransmitter systems, which act on a large number of different mechanisms, showed a significant (yet small) positive effect size of 0.10 (k = 51, p = 0.023; 95% CI = 0.01 to 0.18) on overall cognition. Cognitive enhancers were not superior to placebo for separate cognitive domains. When analyzing each neurotransmitter system separately, agents acting predominantly on the glutamatergic system showed a small significant effect on overall cognition (k = 29, Hedges’ g = 0.19, p = 0.01), as well as on working memory (k = 20, Hedges’ g = 0.13, p = 0.04). A sub-analysis of cholinesterase inhibitors (ChEI) showed a small effect on working memory (k = 6, Hedges’ g = 0.26, p = 0.03). Other sub-analyses were positively nonsignificant, which may partly be due to the low number of studies we could include per neurotransmitter system. Overall, this meta-analysis showed few favorable effects of cognitive enhancers for patients with schizophrenia, partly due to lack of power. There is a lack of studies involving agents acting on other than glutamatergic and cholinergic systems, especially of those targeting the dopaminergic system.

Augmentation strategies for clozapine refractory schizophrenia: A systematic review and meta-analysis

BACKGROUND

Although clozapine is the most effective medication for treatment refractory schizophrenia, only 40% of people will meet response criteria. We therefore undertook a systematic review and meta-analysis of global literature on clozapine augmentation strategies.

METHODS

We systematically reviewed PubMed, PsycInfo, Embase, Cochrane Database, Chinese Biomedical Literature Service System and China Knowledge Resource Integrated Database for randomised control trials of augmentation strategies for clozapine resistant schizophrenia. We undertook pairwise meta-analyses of within-class interventions and, where possible, frequentist mixed treatment comparisons to differentiate treatment effectiveness Results: We identified 46 studies of 25 interventions. On pairwise meta-analyses, the most effective augmentation agents for total psychosis symptoms were aripiprazole (standardised mean difference: 0.48; 95% confidence interval: -0.89 to -0.07) fluoxetine (standardised mean difference: 0.73; 95% confidence interval: -0.97 to -0.50) and, sodium valproate (standardised mean difference: 2.36 95% confidence interval: -3.96 to -0.75). Memantine was effective for negative symptoms (standardised mean difference: -0.56 95% confidence interval: -0.93 to -0.20). However, many of these results included poor-quality studies. Single studies of certain antipsychotics (penfluridol), antidepressants (paroxetine, duloxetine), lithium and Ginkgo biloba showed potential, while electroconvulsive therapy was highly promising. Mixed treatment comparisons were only possible for antipsychotics, and these gave similar results to the pairwise meta-analyses.

CONCLUSIONS

On the basis of the limited data available, the best evidence is for the use of aripiprazole, fluoxetine and sodium valproate as augmentation agents for total psychosis symptoms and memantine for negative symptoms. However, these conclusions are tempered by generally short follow-up periods and poor study quality.

Using EEG-Guided Basket and Umbrella Trials in Psychiatry: A Precision Medicine Approach for Cognitive Impairment in Schizophrenia

Due to advances over the last several decades, many fields of medicine are moving toward a precision medicine approach where treatments are tailored to nuanced patient factors. While in some disciplines these innovations are commonplace leading to unique biomarker-guided experimental medicine trials, there are no such analogs in psychiatry. In this brief review, we will overview two unique biomarker-guided trial designs for future use in psychiatry: basket and umbrella trials. We will illustrate how such trials could be useful in psychiatry using schizophrenia as a candidate illness, the EEG measure mismatch negativity as the candidate biomarker, and cognitive impairment as the target disease dimension.

Adjunctive memantine for schizophrenia: a meta-analysis of randomized, double-blind, placebo-controlled trials

BACKGROUND

Dysfunction of N-methyl-D-aspartate receptor (NMDAR) is involved in the pathophysiology of schizophrenia. A meta-analysis of randomized controlled trials (RCTs) was conducted to examine the efficacy and safety of memantine, a non-competitive NMDAR antagonist, in the treatment of schizophrenia.

METHODS

Standardized/weighted mean differences (SMDs/WMDs), risk ratio (RR), and their 95% confidence intervals (CIs) were calculated and analyzed.

RESULTS

Included in the meta-analysis were eight RCTs (n = 452) of 11.5 ± 2.6 weeks duration, with 229 patients on memantine (20 mg/day) and 223 patients on placebo. Adjunctive memantine outperformed placebo in the measures of Positive and Negative Syndrome Scale and Brief Psychiatric Rating Scale negative symptoms [SMD: -0.63 (95% CI -1.10 to -0.16), p = 0.009, I 2 = 77%], but not in the total, positive and general symptoms [SMD: -0.46 to -0.08 (95% CI -0.93 to 0.22), p = 0.06-0.60, I 2 = 0-74%] or the Clinical Global Impression Severity Scale [WMD: 0.04 (95% CI -0.24 to 0.32), p = 0.78]. The negative symptoms remained significant after excluding one outlying RCT [SMD: -0.41 (95% CI -0.72 to -0.11), p = 0.008, I 2 = 47%]. Compared with the placebo group, adjunctive memantine was associated with significant improvement in neurocognitive function using the Mini-Mental State Examination (MMSE) [WMD: 3.09, (95% CI 1.77-4.42), p < 0.00001, I 2 = 22%]. There was no significant difference in the discontinuation rate [RR: 1.34 (95% CI 0.76-2.37), p = 0.31, I 2 = 0%] and adverse drug reactions between the two groups.

CONCLUSIONS

This meta-analysis showed that adjunctive memantine appears to be an efficacious and safe treatment for improving negative symptoms and neurocognitive performance in schizophrenia. Higher quality RCTs with larger samples are warranted to confirm these findings.

Medications Used for Cognitive Enhancement in Patients With Schizophrenia, Bipolar Disorder, Alzheimer's Disease, and Parkinson's Disease

BACKGROUND/AIMS

Cognitive impairment, which frequently occurs in patients with schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease, has a significant impact on the daily lives of both patients and their family. Furthermore, since the medications used for cognitive enhancement have limited efficacy, the issue of cognitive enhancement still remains a clinically unsolved challenge.

SAMPLING AND METHODS

We reviewed the clinical studies (published between 2007 and 2017) that focused on the efficacy of medications used for enhancing cognition in patients with schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease.

RESULTS

Acetylcholinesterase inhibitors and memantine are the standard treatments for Alzheimer's disease and Parkinson's disease. Some studies have reported selective cognitive improvement in patients with schizophrenia following galantamine treatment. Newer antipsychotics, including paliperidone, lurasidone, aripiprazole, ziprasidone, and BL-1020, have also been reported to exert cognitive benefits in patients with schizophrenia. Dopaminergic medications were found to improve language function in patients with Parkinson's disease. However, no beneficial effects on cognitive function were observed with dopamine agonists in patients with schizophrenia. The efficacies of nicotine and its receptor modulators in cognitive improvement remain controversial, with the majority of studies showing that varenicline significantly improved the cognitive function in schizophrenic patients. Several studies have reported that N-methyl-d-aspartate glutamate receptor (NMDAR) enhancers improved the cognitive function in patients with chronic schizophrenia. NMDAR enhancers might also have cognitive benefits in patients with Alzheimer's disease or Parkinson's disease. Raloxifene, a selective estrogen receptor modulator, has also been demonstrated to have beneficial effects on attention, processing speed, and memory in female patients with schizophrenia.

CONCLUSION

Clinical trials with larger sample sizes evaluating comprehensive cognitive domains are warranted to examine the efficacy of medications in cognitive enhancement in patients with schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease.

Single-Dose Memantine Improves Cortical Oscillatory Response Dynamics in Patients with Schizophrenia

Aberrant gamma-band (30-80 Hz) oscillations may underlie cognitive deficits in schizophrenia (SZ). Gamma oscillations and their regulation by NMDA receptors can be studied via their evoked power (γEP) and phase locking (γPL) in response to auditory steady-state stimulation; these auditory steady-state responses (ASSRs) may be biomarkers for target engagement and early therapeutic effects. We previously reported that memantine, an NMDA receptor antagonist, enhanced two biomarkers of early auditory information processing: prepulse inhibition and mismatch negativity (MMN) in SZ patients and healthy subjects (HS). Here, we describe memantine effects on γEP and γPL in those subjects. SZ patients (n=18) and HS (n=14) received memantine 20 mg (p.o.) and placebo over 2 test days in a double-blind, randomized, counterbalanced, cross-over design. The ASSR paradigm (1 ms, 85 dB clicks in 250-0.5 s trains at a frequency of 40 Hz; 0.5 s inter-train interval) was used to assess γEP and γPL. SZ patients had reduced γEP and γPL; memantine enhanced γEP and γPL (p<0.025 and 0.002, respectively) in both SZ and HS. In patients, significant correlations between age and memantine effects were detected for γEP and γPL: greater memantine sensitivity on γEP and γPL were present in younger SZ patients, similar to our reported findings with MMN. Memantine acutely normalized cortical oscillatory dynamics associated with NMDA receptor dysfunction in SZ patients. Ongoing studies will clarify whether these acute changes predict beneficial clinical, neurocognitive and functional outcomes. These data support the use of gamma-band ASSR as a translational end point in pro-cognitive drug discovery and early-phase clinical trials.

Translating advances in the molecular basis of schizophrenia into novel cognitive treatment strategies

The presence and severity of cognitive symptoms, including working memory, executive dysfunction and attentional impairment, contributes materially to functional impairment in schizophrenia. Cognitive symptoms have proved to be resistant to both first- and second-generation antipsychotic drugs. Efforts to develop a consensus set of cognitive domains that are both disrupted in schizophrenia and are amenable to cross-species validation (e.g. the National Institute of Mental Health Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia and Research Domain Criteria initiatives) are an important step towards standardization of outcome measures that can be used in preclinical testing of new drugs. While causative genetic mutations have not been identified, new technologies have identified novel genes as well as hitherto candidate genes previously implicated in the pathophysiology of schizophrenia and/or mechanisms of antipsychotic efficacy. This review comprises a selective summary of these developments, particularly phenotypic data arising from preclinical genetic models for cognitive dysfunction in schizophrenia, with the aim of indicating potential new directions for pro-cognitive therapeutics. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Memantine add-on to antipsychotic treatment for residual negative and cognitive symptoms of schizophrenia: a meta-analysis

RATIONALE

We examined whether memantine add-on to antipsychotic treatment is beneficial in schizophrenia treatment.

OBJECTIVE

This systematic review and meta-analysis aimed to achieve stronger evidence on the efficacy and safety of memantine add-on for treating schizophrenia.

METHODS

We analyzed double-blind, randomized, placebo-controlled trials of memantine add-on treatment in schizophrenia patients receiving antipsychotics. The primary outcomes were amelioration of negative symptoms and all-cause discontinuation. Dichotomous outcomes are presented as risk ratios (RRs), and continuous outcomes are presented as mean differences (MDs) or standardized mean differences (SMDs).

RESULTS

Eight studies (n = 448) were included. Although memantine add-on treatment was superior to placebo for ameliorating negative symptoms (SMD = -0.96, p = 0.006, I ² = 88%; N = 7, n = 367) in the Positive and Negative Syndrome Scale general subscale (MD = -1.62, p = 0.002, I ² = 0%; N = 4, n = 151) and Mini-Mental Status Examination score (MD = -3.07, p < 0.0001, I ² = 21%; N = 3, n = 83), there were no statistically significant differences in the amelioration of overall (SMD = -0.75, p = 0.06, I ²  = 86%; N = 5, n = 271), positive (SMD = -0.46, p = 0.07, I ² = 80%; N = 7, n = 367), and depressive symptoms (SMD = -0.127, p = 0.326, I ² = 0%; N = 4, n = 201); all-cause discontinuation (RR = 1.34, p = 0.31, I ² = 0%; N = 8, n = 448); and individual adverse events (fatigue, dizziness, headache, nausea, constipation) between the groups. For negative symptoms, the significant heterogeneity disappeared when risperidone studies alone were considered (I ² = 0%). However, memantine add-on treatment remained superior to placebo (SMD = -1.29, p = 0.00001). Meta-regression analysis showed that patient age was associated with memantine-associated amelioration of negative symptoms (slope = 0.171, p = 0.0206).

CONCLUSIONS

Memantine add-on treatment may be beneficial for treating psychopathological symptoms (especially negative symptoms) in schizophrenia patients. The negative-symptom effect size may be associated with younger adult schizophrenia patients.

Positive Modulatory Interactions of NMDA Receptor GluN1/2B Ligand Binding Domains Attenuate Antagonists Activity

N-methyl D-aspartate receptors (NMDAR) play crucial role in normal brain function and pathogenesis of neurodegenerative and psychiatric disorders. Functional tetra-heteromeric NMDAR contains two obligatory GluN1 subunits and two identical or different non-GluN1 subunits that include six different gene products; four GluN2 (A–D) and two GluN3 (A–B) subunits. The heterogeneity of subunit combination facilities the distinct function of NMDARs. All GluN subunits contain an extracellular N-terminal Domain (NTD) and ligand binding domain (LBD), transmembrane domain (TMD) and an intracellular C-terminal domain (CTD). Interaction between the GluN1 and co-assembling GluN2/3 subunits through the LBD has been proven crucial for defining receptor deactivation mechanisms that are unique for each combination of NMDAR. Modulating the LBD interactions has great therapeutic potential. In the present work, by amino acid point mutations and electrophysiology techniques, we have studied the role of LBD interactions in determining the effect of well-characterized pharmacological agents including agonists, competitive antagonists, and allosteric modulators. The results reveal that agonists (glycine and glutamate) potency was altered based on mutant amino acid sidechain chemistry and/or mutation site. Most antagonists inhibited mutant receptors with higher potency; interestingly, clinically used NMDAR channel blocker memantine was about three-fold more potent on mutated receptors (N521A, N521D, and K531A) than wild type receptors. These results provide novel insights on the clinical pharmacology of memantine, which is used for the treatment of mild to moderate Alzheimer's disease. In addition, these findings demonstrate the central role of LBD interactions that can be exploited to develop novel NMDAR based therapeutics.

Symptomatic thinking: the current state of Phase III and IV clinical trials for cognition in schizophrenia

Research indicates that relieving the cognitive and negative symptoms of schizophrenia is crucial for improving patient quality of life. However effective pharmacotherapies for cognitive and negative symptoms do not currently exist. A review of ongoing Phase III clinical trials indicates that, despite numerous compounds being investigated for cognition in schizophrenia, few are actually novel and most are not backed by empirically driven preclinical research efforts. Based on these trials, and a general disinvestment in development of novel therapies for schizophrenia, the likelihood of a major advancement in treating cognitive differences in schizophrenia does not look promising. Possible ways in which the remaining resources for development of novel treatment for schizophrenia can best be leveraged are discussed.

Efficacy of Memantine in Schizophrenic Patients: A Systematic Review

Several evidences support the hypothesis that glutamatergic dysfunction may be implicated in the pathogenesis of schizophrenia and in the last few years great interest has been focused on the role of the N-methyl-D-aspartate receptor (NMDAR). Glutamate is the main excitatory neurotransmitter in human CNS and it plays a prominent role in synaptic plasticity, learning, and memory and other cognitive functions. Increasing interest in memantine add-on therapy in schizophrenic patients with negative and cognitive symptoms may suggest that memantine could be a new promising treatment in schizophrenia. The aim of this update was to evaluate clinical data about the memantine effectiveness in schizophrenic patients. Our systematic review of the literature highlights that memantine therapy in schizophrenic patients seems to improve mainly negative symptoms while positive symptoms and cognitive symptoms did not improve significantly.

Adjunctive memantine in clozapine-treated refractory schizophrenia: an open-label 1-year extension study

BACKGROUND

In a recent placebo-controlled, double-blind crossover trial (n = 52), significant beneficial effects on memory (d = 0.30) and negative symptoms (d = 0.29) were found after 12 weeks of memantine augmentation in patients with clozapine-refractory schizophrenia. In this open-label 1-year extension study we report the long-term effects and tolerability of memantine add-on therapy to clozapine.

METHOD

Completers of the first trial who experienced beneficial effects during 12 weeks of memantine treatment received memantine for 1 year. Primary endpoints were memory and executive function using the Cambridge Neuropsychological Test Automated Battery, the Positive and Negative Syndrome Scale (PANSS), and the Clinical Global Impression Severity Scale (CGI-S).

RESULTS

Of 31 randomized controlled trial completers who experienced beneficial effects from memantine, 24 received memantine for 1 year. The small improvement in memory found in the memantine condition in the placebo-controlled trial remained stable in the extension study. Executive function did not improve. After 26 weeks of memantine add-on therapy to clozapine, PANSS negative symptoms (r = 0.53), PANSS positive symptoms (r = 0.50) and PANSS total symptoms (r = 0.54) significantly improved. Even further significant improvement in all these measures was observed between 26 weeks and 52 weeks of memantine, with effect sizes varying from 0.39 to 0.51. CGI-S showed a non-significant moderate improvement at 26 weeks (r = 0.36) and 52 weeks (r = 0.34). Memantine was well tolerated without serious adverse effects.

CONCLUSIONS

In the 1-year extension phase the favourable effect of adjunctive memantine on memory was sustained and we observed further improvement of negative, positive and overall symptoms in patients with clozapine-treated refractory schizophrenia.