A double-blind, cross-over comparison of the effects of amantadine or placebo on visuomotor and cognitive function in medicated schizophrenia patients

Amantadine: reappraisal of the timeless diamond-target updates and novel therapeutic potentials

The aim of the current review was to provide a new, in-depth insight into possible pharmacological targets of amantadine to pave the way to extending its therapeutic use to further indications beyond Parkinson's disease symptoms and viral infections. Considering amantadine's affinities in vitro and the expected concentration at targets at therapeutic doses in humans, the following primary targets seem to be most plausible: aromatic amino acids decarboxylase, glial-cell derived neurotrophic factor, sigma-1 receptors, phosphodiesterases, and nicotinic receptors. Further three targets could play a role to a lesser extent: NMDA receptors, 5-HT3 receptors, and potassium channels. Based on published clinical studies, traumatic brain injury, fatigue [e.g., in multiple sclerosis (MS)], and chorea in Huntington's disease should be regarded potential, encouraging indications. Preclinical investigations suggest amantadine's therapeutic potential in several further indications such as: depression, recovery after spinal cord injury, neuroprotection in MS, and cutaneous pain. Query in the database http://www.clinicaltrials.gov reveals research interest in several further indications: cancer, autism, cocaine abuse, MS, diabetes, attention deficit-hyperactivity disorder, obesity, and schizophrenia.

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.

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.

Amantadine for Antipsychotic-Related Weight Gain: Meta-Analysis of Randomized Placebo-Controlled Trials

PURPOSE

Weight gain associated with antipsychotics in schizophrenia has been an ongoing concern. This meta-analysis examined the efficacy and safety of amantadine as an adjunctive treatment of weight gain in schizophrenia by systematically searching and analyzing randomized controlled trials (RCTs). RCTs comparing adjunctive amantadine with placebo in adult patients with schizophrenia were included in the meta-analysis.

METHODS

Two independent investigators searched the literature and extracted data. Weighted and standardized mean differences (WMDs/SMDs) and risk ratio ± 95% confidence intervals were calculated.

RESULTS

Five RCTs (n = 265) with double-blinded design lasting 8.2 ± 5.9 weeks were included in the analysis. Amantadine outperformed placebo regarding weight reduction with moderate effect size (trials, 3; n = 205; WMD -2.22 kg; P = 0.001, I = 45%). Amantadine also outperformed placebo at endpoint in the negative symptom (the Positive and Negative Syndrome Scale [PANSS] [1 trial] and the Scale for the Assessment of Negative Symptoms [1 trial]) scores (trials, 2; n = 84; SMD, -0.56; P = 0.01, I = 12%), but not in the PANSS total scores (trials, 2) (SMD, -0.31; P = 0.16, I = 0%) and the positive symptom (PANSS [1 trial] and the Scale for the Assessment of Positive Symptoms [1 trial]) scores (SMD, 0.13; P = 0.54, I = 0%). Except for insomnia (P = 0.007; number needed to harm, 6; 95% confidence interval, 4-16), all-cause discontinuation (risk ratio, 1.12; P = 0.54, I = 0%) and other adverse events were similar between the amantadine and placebo groups.

CONCLUSIONS

According to this meta-analysis of 5 RCTs, adjunctive amantadine seems to be an effective option for attenuating antipsychotic-related weight gain in patients with schizophrenia. More RCTs are needed to inform clinical recommendations.

NMDA receptor antagonists interventions in schizophrenia: Meta-analysis of randomized, placebo-controlled trials

BACKGROUND

We examined whether N-methyl d-aspartate (NMDA) receptor antagonists as adjunctive therapy have therapeutic potential for schizophrenia treatment.

METHOD

Systematic review of PubMed, Cochrane Library, PsycINFO and Google Scholar up until October 2012 and meta-analysis of randomized placebo-controlled trials were performed. Risk ratio (RR), 95% confidence intervals (CI), numbers-needed-to-harm (NNH), and standardized mean difference (SMD) were calculated.

RESULTS

Results were across 8 studies and 406 patients (85.5% schizophrenia related disorder and 14.5% bipolar disorder) were included (amantadine: 5 trials and 220 patients, memantine: 3 trials and 186 patients). NMDA receptor antagonists (NMDAR-ANTs) as adjunctive therapy were not superior to placebo in overall (SMD = -0.25, CI = -0.72, 0.23, p = 0.31, N = 6, n = 347), positive symptoms (SMD = -0.20, CI = -0.70, 0.31, p = 0.44, N = 4, n = 205), and negative symptoms (SMD = -0.69, CI = -1.65, 0.27, p = 0.16, N = 4, n = 205), and Clinical Global Impression Severity scale (SMD = -0.27, CI = -1.20, 0.65, p = 0.56, N = 3, n = 177). There was also no significant difference in discontinuation rate between NMDAR-ANTs and placebo treatments (all cause: RR = 1.23, CI = 0.89-1.70, p = 0.20, N = 8, n = 396, side effects: RR = 1.86, CI = 0.84-4.13, p = 0.13, N = 6, n = 359, inefficacy/worsening psychosis: RR = 0.70, CI = 0.20-2.38, p = 0.56, N = 7, n = 380). However, memantine was favorable compared with placebo in Mini-Mental State Examination in schizophrenia (SMD = -0.77, CI = -1.27, -0.28, p = 0.002, N = 3, n = 71). While NMDAR-ANTs caused weight loss compared with placebo (SMD = -0.42, CI = -0.73, -0.11, p = 0.008, N = 3, n = 165), amantadine caused more frequent insomnia than placebo (RR = 3.83, CI = 1.41-10.38, p = 0.008, NNH = 9, p = 0.002, N = 2, n = 147).

CONCLUSION

Our results indicate that NMDAR-ANTs as adjunctive therapy may improve cognitive function in patients with schizophrenia. Because the included studies were small, a replication study using larger samples is needed.

Adjunctive memantine therapy for cognitive impairment in chronic schizophrenia: a placebo-controlled pilot study

OBJECTIVE

To investigate the effects of memantine, an N-methyl-d-aspartate (NMDA) receptor antagonist, on cognitive impairments in patients with chronic schizophrenia.

METHODS

A 12-week, placebo-controlled trial was conducted to determine the effectiveness of memantine as an adjunctive treatment with conventional antipsychotic medications in 26 patients with chronic schizophrenia. The subjects were evaluated with the Korean version of the Mini-Mental State Examination (K-MMSE), the Positive and Negative Syndrome Scale (PANSS), the Hamilton Rating Scale for Depression (HAM-D), and a standard neuropsychological screening test.

RESULTS

Memantine treatment was not associated with significantly improved cognitive test scores compared with the placebo control treatment. An improvement in the scores on the PANSS negative subscale was noted with memantine, but it was not significant.

CONCLUSION

Adjunctive memantine treatment did not improve cognitive functioning or affect psychopathology in patients with chronic schizophrenia in the present study. Memantine, however, was tolerated well and did not exacerbate positive symptoms in patients with chronic schizophrenia.

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

BACKGROUND

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

OBJECTIVE

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

DATA SOURCES

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

STUDY SELECTION

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

DATA EXTRACTION

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

RESULTS

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

CONCLUSIONS

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

Pharmacological strategies for enhancing cognition in schizophrenia

Researchers have long recognized that individuals with schizophrenia experience challenges in a wide range of cognitive domains, and research on cognitive impairment in schizophrenia is not a recent phenomena. However, the past 10-20 years have seen an increasing recognition of the central importance of cognition to understanding function and outcome in this illness (Green et al. in Schizophr Bull 26:119-136, 2000), an awareness that has shifted the emphasis of at least some work on schizophrenia. More specifically, there has been a rapidly growing body of work on methods of enhancing cognition in schizophrenia, as a means to potentially facilitate improved outcome and quality of life for individuals with this debilitating illness. The current chapter reviews the results of a range of studies examining adjunctive pharmacological treatments to enhance cognition in schizophrenia using a range of designs, including single-dose studies, open-label repeated dosing studies, and double-blind parallel group and crossover designs with repeated dosing. Although many of the single-dose and open-label studies have suggested positive cognitive effects from a range of agents, few of the larger-scale double-blind studies have generated positive results. The current state of results may reflect the need to identify alternative molecular mechanisms for enhancing cognition in schizophrenia or the need to reconceptualize the ways in which pharmacological agents may improve cognition in this illness, with a concomitant change in the traditional clinical trial study design used in prior studies of cognitive enhancement in schizophrenia.

Impaired recognition of happy, sad and neutral expressions in schizophrenia is emotion, but not valence, specific and context dependent

It is not clear whether the deficits in emotion perception in schizophrenia are distinct from cognitive impairments or affect some emotions more than others. We tested the hypothesis that the emotion perception deficit in schizophrenia is valence specific. Participants comprised 75 chronic schizophrenia patients and 77 healthy controls who were asked to identify happy, sad and neutral facial emotional expressions. A test of facial identity recognition was also performed. Processing of happy, sad and neutral expressions differed in accuracy, processing strategy and efficiency. Patients were impaired on all parameters, but the valence-related pattern of performance did not differ in the two groups. Compared with healthy individuals, schizophrenia patients were more impaired in the processing of facial emotions than identity. Processing of neutral expressions was context dependent. Emotion impairment in schizophrenia appears to be selective for the emotion domain but not specific emotions. Test context influences how neutral facial expressions are processed.

Identifying and treating cognitive impairment in bipolar disorder

OBJECTIVES

The presence of cognitive deficits has become increasingly appreciated across all phases of bipolar disorder. The present review sought to identify domains of cognitive dysfunction, methods of assessment, discrimination of iatrogenic from illness-specific etiologies, and pharmacologic strategies to manage cognitive problems in patients with bipolar disorder.

METHODS

A selective literature review was performed focusing on studies of descriptive phenomenology and pharmacologic intervention (favoring randomized comparisons when existent but open trials or case reports when not) involving cognition in bipolar disorder populations, healthy volunteers, or other clinical populations. Identification was made of (i) practical strategies for clinical assessment and management of cognitive complaints, (ii) limitations of existing intervention studies, and (iii) recommendations for the design and direction of future research.

RESULTS

Cognitive deficits involving attention, executive function, and verbal memory are evident across all phases of bipolar disorder. Most existing treatment studies involve nonbipolar populations, prompting caution when extrapolating outcomes to individuals with bipolar disorder. Differentiating medication- from illness-induced cognitive dysfunction requires comprehensive assessment with an appreciation for the cognitive domains most affected by specific medications. No current pharmacotherapies substantially improve cognition in bipolar disorder, although preliminary findings suggest some potential value for adjunctive stimulants such as modafinil and novel experimental agents.

CONCLUSIONS

Circumscribed cognitive deficits may be both iatrogenic and intrinsic to bipolar disorder. Optimal management hinges on a knowledge of illness-specific cognitive domains as well as of the beneficial or adverse cognitive profiles of common psychotropic medications.

Analysis of cognitive performance in schizophrenia patients and healthy individuals with unsupervised clustering models

Currently, assignment of cognitive test results to particular cognitive domains is guided by theoretical considerations and expert judgments which may vary. More objective means of classification may advance understanding of the relationships between test performance and the cognitive functions probed. We examined whether "atheoretical" analyses of cognitive test data can help identify potential hidden structures in cognitive performance. Novel data-mining methods which "let the data talk" without a priori theoretically bound constraints were used to analyze neuropsychological test results of 75 schizophrenia patients and 57 healthy individuals. The analyses were performed on the combined sample to maximize the "atheoretical" approach and allow it to reveal different structures of cognition in patients and controls. Analyses used unsupervised clustering methods, including hierarchical clustering, self-organizing maps (SOM), k-means and supermagnetic clustering (SPC). The model revealed two major clusters containing accuracy and reaction time measures respectively. The sensitivity (75% versus 52%) and specificity (95% versus 77% ) of these clusters for diagnosing schizophrenia differed. Downstream branching was influenced by stimulus domain. Predictions arising from this "atheoretical" model are supported by evidence from published studies. This preliminary study suggests that appropriate application of data-mining methods may contribute to investigation of cognitive functions.

Verbal as well as spatial working memory predicts visuospatial processing in male schizophrenia patients

BACKGROUND

Visuospatial processing (VSP) is impaired in schizophrenia. Recent studies showed significant associations between the Judgment of Line Orientation (JLO) test, a common test of VSP and Verbal (VWM) as well as Spatial (SWM) working memory. VWM and SWM show different associations with various genes so subgroups of patients with similar VSP but different WM impairment profiles may vary in genetic associations. In this study we investigated the relationship among VSP, VWM and SWM.

METHODS

Sixty seven men with schizophrenia and 51 healthy men completed computerized JLO and tests of VWM (digit span), and SWM (Dot test). Tests of attention (CPT) and psychomotor processing speed (Finger Tap) were also included.

RESULTS

Patients' performance was impaired on all tests. Multivariate regression with JLO as the outcome variable and VWM, SWM, attention, psychomotor processing speed and interactions between group and these variables, as predictors showed significant contribution of VWM and SWM. The model explained 34.4% of the variance (R(2)=0.344).

CONCLUSION

VSP, as measured by JLO, receives independent contributions from VWM and SWM. Patient subgroups matched for VSP may differ in the relative contributions and impairments of VWM and SWM. Such heterogeneity may limit the usefulness of VSP in genetic studies. The possibility that WM may be more useful than VSP in this regard deserves further study.

Addition of memantine to antipsychotic treatment in schizophrenia inpatients with residual symptoms: A preliminary study

BACKGROUND

Schizophrenia is comprised of several debilitating symptoms. Antipsychotics offer an effective treatment for positive symptoms, while the negative signs and cognitive deficits are usually treatment-resistant. It was suggested that glutamate dysregulation may be involved in the neuropathology of schizophrenia, mainly through NMDA dysfunction. We hypothesized that addition of memantine, a weak non-selective NMDA receptor antagonist approved for dementia, to antipsychotics would improve the clinical status of un-remitted schizophrenia patients, notably the negative signs and cognitive deficits.

METHODS

Seven schizophrenia patients, were included in a six-week open-label study, with weekly increasing dosage (5, 10, 15, 20 mg) of memantine added to their on-going antipsychotic treatment.

RESULTS

We found a significant improvement of the PANSS score (baseline 116.28+/-21.9 vs. 97.86+/-24.48 after six weeks, t=5.98, p<0.001) with the most prominent improvement (21%) in negative signs sub-scale (baseline 40+/-6.38 vs. 31.71+/-7.76 after six weeks, t=5.87, p<0.001). Cognitive status, measured with the Neurobehavioral Cognitive Examination (NCSE) and Clock Drawing Test (CDT) showed no improvement.

CONCLUSION

Memantine addition to antipsychotic treatment, in schizophrenia patients might improve their clinical status, primarily the negative signs, but not their cognitive deficits. Further research is needed to replicate these observations.