Memantine

Case report: a unique presentation of memantine overdose causing echolalia and hypertension

BACKGROUND

Since 2003 when memantine was first approved for use in the management of moderate-severe Alzheimer's dementia, its use has become more widespread and is being explored in other diseases like neuropathic pain, epilepsy, and mood disorders. Our case uniquely highlights two important adverse effects in a patient who overdosed on memantine. One is hypertension, which is easy to overlook as a medication side effect. The other is echolalia which is the repetition of words and phrases spoken by another person. It is commonly seen in children with autism spectrum disorder and has been reported in older adults with head injuries, delirium, and neurocognitive disorders. The aim of this patient story is to highlight the importance of medication reconciliation with caregivers and knowledge of adverse drug reactions in patient management. This case report has been presented previously in the form of an abstract at the American Geriatrics Society Presidential poster session in May 2023.

CASE PRESENTATION

Our patient is an 86-year-old man with mild dementia and hypertension, who was brought to the emergency department (ED) due to abrupt onset of altered mental status and auditory hallucinations. Investigations including blood work, CT head and an electroencephalogram (EEG) did not reveal an etiology for this change in his condition. Due to elevated blood pressure on presentation, a nicardipine drip was started, and he was given IV midazolam to assist with obtaining imaging. While reviewing medications with his daughter, it was noted that sixty memantine pills were missing from the bottle. Poison control was contacted and they confirmed association of these features with memantine. With supportive care, his symptoms resolved in less than 100 h, consistent with the half-life of memantine. Notably, our patient was started on Memantine one month prior to this presentation.

CONCLUSIONS

Hypertensive urgency and echolalia were the most striking symptoms of our patient's presentation. Though hypertension is a known sign of memantine overdose, it can easily be contributed to medication non-compliance in patients with dementia, being treated for hypertension. According to our literature review, this the first case of memantine overdose presenting with echolalia, a sign that is not commonly associated with adverse reactions to medications. This highlights the importance of an early medication review, especially with caregivers of people with dementia.

Sundowning in Patients with Dementia: Identification, Prevalence, and Clinical Correlates

BACKGROUND

The term sundowning is used to describe the emergence or worsening of neuropsychiatric symptoms in late afternoon or early evening in people with dementia.

OBJECTIVE

Our aim was to evaluate sundowning's prevalence and clinical manifestations among patients attending a tertiary memory clinic and to investigate its clinical and neuropsychological correlates.

METHODS

Patients with dementia attending our memory clinic were enrolled in the study. Sundowning was identified through a specifically designed questionnaire. Sociodemographic and clinical features of sundowners and non-sundowners were compared, and a logistic regression was performed to identify the variables associated with the phenomenon. A subgroup of patients underwent a complete neuropsychological assessment.

RESULTS

Among 184 recruited patients, 39 (21.2%) exhibited sundowning, mostly expressed as agitation (56.4%), irritability (53.8%), and anxiety (46.2%). Sundowners were significantly older, had a later dementia onset, exhibited more severe cognitive and functional impairment, more frequent nocturnal awakenings, and hearing loss relative to non-sundowners. They were also more likely to use anticholinergic medications and antipsychotics, and less likely to use memantine. In a multi-adjusted model, the factors significantly associated with sundowning were the Clinical Dementia Rating score (OR 3.88, 95% CI 1.39-10.90) and the use of memantine (OR 0.20; 95% CI 0.05-0.74). Participants with and without sundowning obtained similar results in single domain neuropsychological tests.

CONCLUSION

Sundowning is commonly experienced by patients with dementia and appears as a multiply determined condition. Its presence should always be evaluated in clinical practice and a multidimensional approach should be adopted to identify its predictors.

Tau fibril with membrane lipids: Insight from computational modeling and simulations

The microtubule-binding protein tau has been the center of researches concerning Alzheimer's disease (AD) due to several clinical trials of β-amyloid therapies failing recently. The availability of the tau fibril structure from AD brain enables computational modeling studies to calculate binding affinities with different ligands. In this study, the tau paired helical filaments (PHF-Tau) (PDB ID: 5O3L) was used as receptor and interactions with the lipids: 3-alpha-cholesterol; 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; and C18:1 sphingomyelin, were explored with molecular docking, molecular dynamics, and natural bond orbital analysis. Docking sites upon solvation of the protein with transferable interatomic potential-3 points reveal the amphipathic nature of PHF-Tau and molecular dynamics simulations show that the embedded phosphocholine at the tail side gives high potential energy values with some amino acids forming H-bond interactions.

Delirium Superimposed on Dementia in Perioperative Period and Intensive Care

Delirium is a life-threatening condition, the causes of which are still not fully understood. It may develop in patients with pre-existing dementia. Delirium superimposed on dementia (DSD) can go completely unnoticed with routine examination. It may happen in the perioperative period and in the critical care setting, especially in the ageing population. Difficulties in diagnosing and lack of specific pharmacological and non-pharmacological treatment make DSD a seriously growing problem. Patient-oriented, multidirectional preventive measures should be applied to reduce the risk of DSD. For this reason, anesthesiologists and intensive care specialists should be aware of this interesting condition in their everyday clinical practice.

Natural and synthetic drugs used for the treatment of the dementia

This review is devoted to comparative pharmacological analysis of synthetic drugs such as memantine and its isomers, as well as tacrine, velnacrine, rivastigmine, and donepezil, with natural alkaloids, terpenoids, and triterpenoid peroxides, which are used to treat dementia, Alzheimer's and Parkinson's diseases, myasthenia gravis and other neurodegenerative diseases. Recently discovered by French scientists from Marseille triterpenoid hydroperoxides demonstrate high activity as potential therapeutic agents for the treatment of dementia. The information presented in this review is of great interest to pharmacologists, medical chemists, physiologists, neurologists and doctors, as well as for the pharmaceutical industry.

The efficacy and safety of memantine for the treatment of Alzheimer's disease

INTRODUCTION

Currently, five pharmacotherapeutic options are available to treat Alzheimer's disease: memantine; the three cholinesterase inhibitors donepezil, galantamine, and rivastigmine; and combination treatments with memantine and one cholinesterase inhibitor. Selection of the best course of treatment is based upon the evidence gathered by systematic reviews and meta-analyses of randomized controlled trials. Areas covered: This article provides a risk-benefit analysis of these treatments using evidence from meta-analyses on their safety and their efficacy. Expert opinion: Memantine improves cognitive functions and behavioral disturbances more efficiently than the placebo, both as monotherapy and in combination with donepezil. Although memantine monotherapy and combination therapy are associated with a few individual adverse events such as somnolence, it is well-tolerated and its safety (all-cause discontinuation) is comparable or superior to that of the placebo (agitation). Pooled cholinesterase inhibitors are superior to the placebo in the improvement of cognitive functions, but not behavioral disturbances and they are not well-tolerated, as evaluated by the high discontinuation rate. Donepezil (10 mg/day) and oral rivastigmine and galantamine monotherapies carry the risk for some adverse events including gastrointestinal symptoms. Therefore, we consider that combined treatment with memantine and donepezil is the most useful treatment for Alzheimer's disease.

A role for NMDAR-dependent cerebellar plasticity in adaptive control of saccades in humans

BACKGROUND

Saccade pulse amplitude adaptation is mediated by the dorsal cerebellar vermis and fastigial nucleus. Long-term depression at the parallel fibre-Purkinjie cell synapses has been suggested to provide a cellular mechanism for the corresponding learning process. The mechanisms and sites of this plasticity, however, are still debated.

OBJECTIVE

To test the role of cerebellar plasticity phenomena on adaptive saccade control.

METHODS

We evaluated the effect of continuous theta burst stimulation (cTBS) over the posterior vermis on saccade amplitude adaptation and spontaneous recovery of the initial response. To further identify the substrate of synaptic plasticity responsible for the observed adaptation impairment, subjects were pre-treated with memantine, an N-methyl-d-aspartate receptor (NMDAR) antagonist.

RESULTS

Amplitude adaptation was altered by cTBS, suggesting that cTBS interferes with cerebellar plasticity involved in saccade adaptation. Amplitude adaptation and spontaneous recovery were not affected by cTBS when recordings were preceded by memantine administration.

CONCLUSION

The effects of cTBS are NMDAR-dependent and are likely to involve long-term potentiation or long-term depression at specific synaptic connections of the granular and molecular layer, which could effectively take part in cerebellar motor learning.

Use of antidementia drugs and risk of pneumonia in older persons with Alzheimer's disease

INTRODUCTION

Persons with Alzheimer's disease are at an increased risk of pneumonia, but the comparative risks during specific antidementia treatments are not known. We compared the risk of pneumonia in the use of donepezil, rivastigmine (oral, transdermal), galantamine and memantine.

PATIENTS AND METHODS

We used data from a nationwide cohort of community-dwelling individuals diagnosed with Alzheimer's disease during 2005-2011 in Finland, who initiated monotherapy with acetylcholinesterase inhibitor or memantine (n = 65,481). The risk of hospitalization or death due to pneumonia was investigated with Cox proportional hazard models.

RESULTS

The risk of pneumonia was higher in persons using rivastigmine patch (n = 9709) (adjusted hazard ratio (HR) 1.15, 95% confidence interval (CI) 1.04-1.27) and memantine (n = 11,024) (HR 1.59, 95% CI 1.48-1.71) compared with donepezil users (n = 26,416) whereas oral rivastigmine (n = 7384) (HR 1.08, 95% CI 0.98-1.19) and galantamine (n = 10,948) (HR 0.91, 95% CI 0.83-1.00) were not associated with an increased risk. These results did not change when adjusting for comorbid conditions, use of psychotropic drugs or with inverse probability of treatment weighting.

DISCUSSION

The increased risk of pneumonia in this fragile group of aged persons should be taken into account. Memantine is associated with the highest risk in the comparison of antidementia drugs. KEY Message Pneumonia risk is increased in persons with Alzheimer's disease who use memantine or rivastigmine patches.

Visual hallucinations treated with the reinitiation of memantine in a patient with Lewy body dementia

OBJECTIVE

To report on a patient with Lewy body dementia who developed worsening of hallucinations with memantine withdrawal and significant improvement with reinitiation of the drug.

CASE SUMMARY

A 78-year-old man presented to a geriatric psychiatry clinic in March 2011. The patient had experienced gradual memory loss since 2007 and was diagnosed with dementia with Lewy bodies (DLB) in 2009. His medication regimen included donepezil and memantine; his cognitive and functional status appeared stable. Occasional mild visual hallucinations occurred but were not concerning to the patient or his wife. The patient did well to July 2011, when memantine became restricted within the health care institution; memantine was therefore tapered to discontinuation. From July to September 2011, the patient's cognition and function appeared to decline significantly. He also began experiencing severe visual hallucinations daily. Memantine was reinitiated in September 2011 and, within days, the patient was free of hallucinations. By November 2011, his cognition and function were noted to have improved to previous status, and hallucinations were rare.

DISCUSSION

Three small randomized studies and 4 case reports were found addressing the use of memantine for DLB. Both improvement and worsening of hallucinations were noted with memantine use in the case reports, but the studies showed only a small benefit in cognition. However, cognitive and psychiatric symptoms worsened when memantine was discontinued. One study found that Neuropsychiatric-Inventory scores and hallucination scores improved significantly for patients taking memantine.

CONCLUSIONS

The literature investigating the use of memantine for the psychiatric symptoms of DLB is limited but there are data noting results similar to what we observed in our patient when his memantine was discontinued and reinitiated.

Memantine inhibits α3β2-nAChRs-mediated nitrergic neurogenic vasodilation in porcine basilar arteries

Memantine, an NMDA receptor antagonist used for treatment of Alzheimer’s disease (AD), is known to block the nicotinic acetylcholine receptors (nAChRs) in the central nervous system (CNS). In the present study, we examined by wire myography if memantine inhibited α3β2-nAChRs located on cerebral perivascular sympathetic nerve terminals originating in the superior cervical ganglion (SCG), thus, leading to inhibition of nicotine-induced nitrergic neurogenic dilation of isolated porcine basilar arteries. Memantine concentration-dependently blocked nicotine-induced neurogenic dilation of endothelium-denuded basilar arteries without affecting that induced by transmural nerve stimulation, sodium nitroprusside, or isoproterenol. Furthermore, memantine significantly inhibited nicotine-elicited inward currents in Xenopous oocytes expressing α3β2-, α7- or α4β2-nAChR, and nicotine-induced calcium influx in cultured rat SCG neurons. These results suggest that memantine is a non-specific antagonist for nAChR. By directly inhibiting α3β2-nAChRs located on the sympathetic nerve terminals, memantine blocks nicotine-induced neurogenic vasodilation of the porcine basilar arteries. This effect of memantine is expected to reduce the blood supply to the brain stem and possibly other brain regions, thus, decreasing its clinical efficacy in the treatment of Alzheimer’s disease.

Memantine, an NMDA receptor antagonist, differentially influences Go/No-Go performance and fMRI activity in individuals with and without a family history of alcoholism

RATIONALE

Individuals with a family history of alcoholism (family history positive [FHP]) show higher alcoholism rates and are more impulsive than those without such a family history (family history negative [FHN]), possibly due to altered N-methyl-D-aspartate (NMDA) receptor function.

OBJECTIVES

We investigated whether memantine, an NMDA receptor antagonist, differentially influences impulsivity measures and Go/No-Go behavior and fMRI activity in matched FHP and FHN individuals.

METHODS

On separate days, participants received a single dose of 40 mg memantine or identical-appearing placebo.

RESULTS

No group performance differences were observed on placebo for Go correct hit or No-Go false alarm reaction time on the Go/No-Go task. During fMRI, right cingulate activation differed for FHP vs. FHN subjects during No-Go correct rejects. Memantine had attenuated effects in FHP vs. FHN subjects: For No-Go false alarms, memantine was associated with limited reduction in subcortical, cingulate, and temporal regions in FHP subjects and reduced activity in fronto-striatal-parietal networks in FHN subjects. For No-Go correct rejects, memantine (relative to placebo) reduced activity in left cingulate and caudate in FHP but not FHN subjects.

CONCLUSIONS

Lower sensitivity to the effects of memantine in FHP subjects is consistent with greater NMDA receptor function in this group.

A new HPLC method with fluorescence detection for the determination of memantine in human plasma

A sensitive, selective, simple and fast HPLC method based on the formation of derivative with fluorescamine was developed for the determination of memantine (ME) in human plasma. Separation was achieved on a CN column (200 mm×4.6 mm) using acetonitrile-10 mM orthophosphoric acid containing 1 mL/L triethylamine (45:55, v/v) at a flow rate of 1 mL/min. Emission and excitation wavelengths were 480 and 380 nm, respectively. Amantadine was used as an internal standard. Calibration graphs were rectilinear over the range of 1.0-100.0 ng/mL. Limit of detection and limit of quantification were found to be 0.3 and 1.0 ng/mL, respectively. Intra-day and inter-day relative standard deviation values were found to be <2.03%. Average recovery was also found to be around 94%. Proposed method was applied for the pharmacokinetic study in a healthy volunteer after a single oral administration of 20 mg of ME.

Treatment of Alzheimer's disease in Brazil: I. Cognitive disorders

This article reports the recommendations of the Scientific Department of Cognitive Neurology and Aging of the Brazilian Academy of Neurology for the treatment of Alzheimer’s disease (AD) in Brazil, with special focus on cognitive disorders. It constitutes a revision and broadening of the 2005 guidelines based on a consensus involving researchers (physicians and non-physicians) in the field. The authors carried out a search of articles published since 2005 on the MEDLINE, LILACS and Cochrane Library databases. The search criteria were pharmacological and non-pharmacological treatment of cognitive disorders in AD. Studies retrieved were categorized into four classes, and evidence into four levels, based on the 2008 recommendations of the American Academy of Neurology. The recommendations on therapy are pertinent to the dementia phase of AD. Recommendations are proposed for the treatment of cognitive disorders encompassing both pharmacological (including acetyl-cholinesterase inhibitors, memantine and other drugs and substances) and non-pharmacological (including cognitive rehabilitation, physical activity, occupational therapy, and music therapy) approaches. Recommendations for the treatment of behavioral and psychological symptoms of dementia due to Alzheimer’s disease are included in a separate article of this edition.

Steady-state pharmacokinetics of rivastigmine in patients with mild to moderate Alzheimer's disease not affected by co-administration of memantine: an open-label, crossover, single-centre study

BACKGROUND AND OBJECTIVE

It has been shown that combining memantine and a cholinesterase inhibitor, which each affect different neurotransmitter systems, may offer further improvements in efficacy over either treatment alone in patients with Alzheimer's disease. The present study was conducted to determine if memantine has any effects on the steady-state pharmacokinetics of rivastigmine in patients with mild to moderate Alzheimer's disease.

METHODS

Rivastigmine-treated Alzheimer's disease patients who had been maintained on a fixed regimen of twice-daily rivastigmine for >or=2 months were eligible to enter the study. Sixteen patients (seven males and nine females, age range 64-88 years, weight range 51.8-104 kg) were enrolled in this open-label, crossover study, which consisted of a 28-day screening period, a 36-hour baseline period, and a 35-day combination treatment phase. The patients spent the baseline period and day 35 at the study centre, where plasma samples for pharmacokinetic evaluation were taken at specified time intervals over a 10-hour time period. In addition, 10-hour (evening pre-dose) memantine plasma samples were taken on days 21, 34 and 35.

RESULTS

The combination of memantine (10 mg twice daily) with rivastigmine (1.5-6 mg twice daily) was safe and well tolerated. At each dose level of rivastigmine, the area under the concentration-time curve (AUC) values of rivastigmine and its metabolite as well as the metabolite-to-parent AUC ratios were unaffected by co-administration of memantine, confirming the absence of a meaningful pharmacokinetic drug-drug interaction.

CONCLUSION

Under the study conditions, the extent of systemic exposure to rivastigmine and its metabolite NAP226-90 at steady state did not appear to be affected by concomitant administration of memantine.

The after-effect of human theta burst stimulation is NMDA receptor dependent

OBJECTIVE

To provide pharmacological evidence that the after-effects of theta burst stimulation (TBS) involve plasticity like changes in cortical synaptic connections, using the N-methyl-D-aspartate receptor antagonist memantine.

METHODS

We performed a double blind, placebo-controlled study to evaluate the effect of memantine on the response of six healthy volunteers to TBS. We measured rest (RMT) and active (AMT) motor thresholds, and the amplitude of MEPs before and after continuous and intermittent TBS (cTBS/iTBS) after the administration of placebo or memantine.

RESULTS

Memantine had no effect on RMT and AMT, while it blocked the suppressive effect of cTBS and the facilitatory effect of iTBS.

CONCLUSIONS

The effects of iTBS and cTBS rely on NMDARs to produce after-effects in the motor cortex of conscious humans.

SIGNIFICANCE

The NMDA dependency of the after-effects of TBS adds to the understanding of the underlying mechanism of TBS, and suggests that these after-effects are likely to involve plasticity like changes at synaptic connections in motor cortex.

Added therapeutic value of memantine in the treatment of moderate to severe Alzheimer's disease

When evaluating the added therapeutic value of a drug, evidence of greater overall benefit or at least an add-on benefit is increasingly being required. Therefore, cost-effectiveness in addition to clinical efficacy is an important consideration. The efficacy of a drug must be examined on the basis of clinical trials by measuring specific parameters that are affected by the drug (for example blood pressure with antihypertensive treatment). Today not only efficacy but also patient-relevant changes (patient benefits) must be demonstrated for a drug, often by measuring quality of life. In order to evaluate the benefit of monotherapy with the N-methyl-D-aspartate antagonist memantine in the management of moderate to severe Alzheimer's disease, a systematic literature review was conducted. The results showed a benefit for memantine in comparison with placebo in terms of a decrease in nursing care, a delay in care dependency and a delay in admission to nursing homes. In addition, an increase in quality of life has been observed.

Spatial relationship between synapse loss and beta-amyloid deposition in Tg2576 mice

Although there is evidence that beta-amyloid impairs synaptic function, the relationship between beta-amyloid and synapse loss is not well understood. In this study we assessed synapse density within the hippocampus and the entorhinal cortex of Tg2576 mice at 6-18 months of age using stereological methods at both the light and electron microscope levels. Under light microscopy we failed to find overall decreases in the density of synaptophysin-positive boutons in any brain areas selected, but bouton density was significantly decreased within 200 mum of compact beta-amyloid plaques in the outer molecular layer of the dentate gyrus and Layers II and III of the entorhinal cortex at 15-18 months of age in Tg 2576 mice. Under electron microscopy, we found overall decreases in synapse density in the outer molecular layer of the dentate gyrus at both 6-9 and 15-18 months of age, and in Layers II and III of the entorhinal cortex at 15-18 months of age in Tg 2576 mice. However, we did not find overall changes in synapse density in the stratum radiatum of the CA1 subfield. Furthermore, in the two former brain areas we found a correlation between lower synapse density and greater proximity to beta-amyloid plaques. These results provide the first quantitative morphological evidence at the ultrastructure level of a spatial relationship between beta-amyloid plaques and synapse loss within the hippocampus and the entorhinal cortex of Tg2576 mice.

Memantine: a review of its use in Alzheimer's disease

Memantine (Ebixa, Axura, Namenda, Akatinol) is a moderate-affinity, uncompetitive, voltage-dependent, NMDA-receptor antagonist with fast on/off kinetics that inhibits excessive calcium influx induced by chronic overstimulation of the NMDA receptor. Memantine is approved in the US and the EU for the treatment of patients with moderate to severe dementia of the Alzheimer's type. In well designed clinical trials, oral memantine, as monotherapy or in addition to a stable dose of acetylcholinesterase inhibitors, was well tolerated during the treatment of mild to severe Alzheimer's disease for up to 52 weeks. Memantine generally modified the progressive symptomatic decline in global status, cognition, function and behaviour exhibited by patients with moderate to severe Alzheimer's disease in four 12- to 28-week trials. In patients with mild to moderate Alzheimer's disease, data from three 24-week trials are equivocal, although meta-analyses indicate beneficial effects on global status and cognition. Memantine is an effective pharmacotherapeutic agent, and currently the only approved option, for the treatment of moderate to severe Alzheimer's disease.

Pharmacokinetics and disposition of memantine in the arterially perfused bovine eye

PURPOSE

To develop an improved ((1)This is to clearly acknowledge that we have tried to improve an existing model.) arterially perfused bovine eye model and investigate the general ocular disposition of memantine.

MATERIALS AND METHODS

Fresh bovine eyes were prepared by exposing and cannulating one ciliary artery, placing the eye into a perfusion chamber and slowly increasing the rate of perfusion to 1.0 ml/min. Analysis of the arterial perfusion pressure (APP), intraocular pressure (IOP), venous perfusate for glucose consumption and lactate dehydrogenase (LDH) activity, and histopathology ensured viability. Memantine was administered with the perfusate (simulated systemic access), by an intravitreal injection and by topical infusion. At the appropriate time points, the cornea, aqueous humour, sclera, iris-ciliary body, choroid/RPE, retina and vitreous humour were harvested and analysed for memantine.

RESULTS

The preparation remained viable for at least 9 h. At this time, histopathological examination showed mild to moderate deterioration of retinal layers. However, all retinal layers remained well defined and the integrity of the inner limiting membrane and Bruch's membrane were preserved. Glucose consumption, LDH levels and constant APP and IOP showed that correct cannulation and viability was maintained. After administration, memantine accumulated in the melanin rich iris-ciliary body and choroid/RPE. Results following topical administration indicate that substantial concentrations of memantine are present in the retina and choroid/RPE.

CONCLUSIONS

The arterial perfused bovine eye system proved to be a useful system for ocular drug delivery studies. The experimental results indicate that memantine will accumulate in the posterior segment when delivered by the topical route and that melanin-binding may support sustaining significant concentrations in the retina.

Alzheimer Disease and Its Management

Alzheimer disease is a progressive degenerative disorder of the brain characterized by a slow, progressive decline in cognitive function and behavior. As the disease advances, persons with Alzheimer disease have tough time with daily usage of things like using the phone, cooking, handling money, or driving the car. The disease is more common in elder population. It is estimated that Alzheimer disease affects 15 million people worldwide and approximately 4 million Americans. The clinical features of Alzheimer disease overlaps with common signs of aging, and other types of dementia, hence the diagnosis remains difficult. The neuropathologic hallmarks of the disorder are amyloid-rich senile plaques, neurofibrillary tangles, and neuronal degeneration. Drugs approved for treating Alzheimer disease include acetylcholinesterase inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonist. Caregivers not getting adequate information about Alzheimer disease may believe that nothing can be done to manage its symptoms. Understanding the extent of Alzheimer disease related knowledge can assist disease management that result in improved disease management and reduced care costs. This article attempts to focus on some of the important recent developments in understanding and management of Alzheimer disease.

Evidence for the involvement of L-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of memantine in mice

This study investigated the involvement of the L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the antidepressant-like effect of an acute administration of memantine in the forced swimming test (FST) in mice, since this signaling pathway is supposed to play a significant role in depression. The antidepressant-like effect of memantine (3 mg/kg, i.p.) was prevented by pretreatment with L-arginine (750 mg/kg, i.p.) or S-nitroso-N-acetyl-penicillamine (SNAP, 25 microg/site, i.c.v.), but not with d-arginine (750 mg/kg, i.p.).The treatment of mice with NG-nitro-L-arginine (L-NNA, 0.03 and 0.3 mg/kg, i.p.) potentiated the effect of a subeffective dose of memantine (0.3 mg/kg, i.p.) in the FST. Moreover, the pretreatment of mice with (1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one) (ODQ, 30 pmol/site, i.c.v.) produced a synergistic antidepressant-like effect with subeffective doses of memantine (0.3 and 1 mg/kg, i.p.) in the FST. Furthermore, the reduction in the immobility time elicited by memantine (3 mg/kg, i.p.) in the FST was prevented by pretreatment with sildenafil (5 mg/kg, i.p.). Taken together, the results demonstrate that memantine produced an antidepressant-like effect in the FST that seems to be mediated through an interaction with the L-arginine-NO-cGMP pathway.

[Treatment of Alzheimer's disease: recommendations and suggestions of the Scientific Department of Cognitive Neurology and Aging of the Brazilian Academy of Neurology]

The present recommendations and suggestions on "Treatment of Alzheimer's Disease" were elaborated by a work group constituted by participants of the IV Meeting of Researchers on Alzheimer's Disease and Related Disorders, sponsored by the Scientific Department of Cognitive Neurology and Aging of the Brazilian Academy of Neurology. They comprise topics on pharmacological and non-pharmacological treatment of cognitive impairment and functional decline, as well as of behavioral and psychological symptoms of this dementing disease. Several levels of evidence and of recommendations and suggestions are used for the various proposed drugs, as well as for non-pharmacological treatment, underpinned by a wide national and international bibliographical review.

Steady-state pharmacokinetics and pharmacodynamics of CHF3381, a novel antineuropathic pain agent, in healthy subjects

AIMS

To evaluate the safety, tolerability, pharmacokinetic and pharmacodynamic profiles of CHF3381, a dual NMDA and MAO-A inhibitor, after multiple oral doses in healthy subjects.

METHODS

Forty-eight young males received CHF3381 at doses of 100 mg twice daily, 200 mg twice daily, 400 mg twice daily or placebo for 2 weeks according to a double-blind, randomized, parallel group design. Plasma and urine concentrations of the parent drug and of two major metabolites (CHF3567 and 2-aminoindane) were measured over time. MAO-A activity in plasma was estimated by measuring plasma concentrations of 3,4-dihydroxyphenylglycol. Sustained attention, memory and sedation were assessed throughout the study with standard psychometric tests.

RESULTS

Most of the adverse events were mild in intensity, with dose regimens of 100 mg twice daily and 200 mg twice daily being indistinguishable from placebo. After 400 mg twice daily, the most frequent adverse events were mild dizziness, asthenia and insomnia. At steady-state, 400 mg twice daily slightly increased supine heart rate (+ 9 +/- 2 beats min(-1)) and diastolic blood pressure (+6 +/- 2 mmHg) compared with placebo. There were no dose-dependent or consistent effects of CHF3381 on attention, motor co-ordination or memory, but 400 mg twice daily significantly decreased alertness compared with placebo. Plasma concentrations of CHF3381 peaked at around 3 h and were dose-proportional. The elimination half-life of CHF3381 was estimated to be 4-6 h. At steady-state, significant CHF3381 plasma concentrations were detected at predose with a modest accumulation (1.3-1.5 times), showing that the drug given twice daily is active over the entire 24 h period. Plasma concentrations of CHF3567 and of 2-aminoindane were also proportional to the dose of CHF3381. CHF3381 dose-dependently inhibited MAO-A activity with peak effects at steady-state of 27 +/- 4%, 46 +/- 2% and 65 +/- 5% after 100 mg twice daily, 200 mg twice daily and 400 mg twice daily, respectively. There were no significant effects of CHF3381 on attention (rapid visual information processing), motor co-ordination (body sway) or memory (learning memory task) at any of the doses. At steady-state, there was a significant decrease in alertness (Bond & Lader visual analogue scale) in the 400 mg twice daily group compared with placebo.

CONCLUSIONS

A twice daily regimen of CHF3381 appears to be adequate from a pharmacokinetic and pharmacodynamic perspective. Plasma concentrations reached with 400 mg twice daily exceeded those observed in animals receiving pharmacologically active doses in chronic pain models.

Dementia of Alzheimer's disease and other neurodegenerative disorders--memantine, a new hope

Alzheimer's disease is the fourth largest cause of death for people over 65 years of age. Dementia of Alzheimer's type is the commonest form of dementia, the other two forms being vascular dementia and mixed dementia. At present, the therapy of Alzheimer's disease is aimed at improving both, cognitive and behavioural symptoms and thereby, quality of life for the patients. Since the discovery of Alzheimer's disease by Alois Alzheimer, many pathological mechanisms have been proposed which led to the testing of various new treatments. Until recently the available drugs for the treatment of Alzheimer's disease are cholinesterase inhibitors, which have limited success because these drugs improve cognitive functions only in mild dementia and cannot stop the process of neurodegeneration. Moreover, drugs of this category show gastrointestinal side effects. As the cells of central and peripheral nervous system cannot regenerate, newer strategies are aimed at preserving the surviving neurons by preventing their degeneration. NMDA-receptor-mediated glutamate excitotoxicity plays a major role in Abeta-induced neuronal death. Hence, it was thought that NMDA receptors could be a promising target for preventing the progression of Alzheimer's disease. All the compounds synthesized initially in this category showed toxicity mainly because of their high affinity for NMDA receptors. Memantine (1-amino adamantane derivative), NMDA-receptor antagonist was reported to be effective therapeutically in Alzheimer's disease. It was available in Germany as well as European Union and has been approved for moderate to severe dementia in United States of America recently. It is an uncompetitive, moderate affinity antagonist of NMDA receptors that inhibits the pathological functions of NMDA receptors while physiological processes in learning and memory are unaffected. Memantine is also reported to have beneficial effects in other CNS disorders viz., Parkinson's disease (PD), stroke, epilepsy, CNS trauma, amyotrophic lateral sclerosis (ALS), drug dependence and chronic pain. Mechanisms of neuroprotection, preclinical and clinical evidence for effectiveness of memantine have been provided. Pharmacology and pharmacokinetics of memantine and other NMDA-receptor antagonists in comparison with currently approved drugs for dementia treatment have been discussed. The focus is on 'glutamate excitotoxicity' and glutamate receptors as drug target. Various other novel strategies for the treatment of dementia of neurodegenerative disorders have also been discussed.

[Memantine: a therapeutic drug for Alzheimer's disease and the comparison with MK-801]

Memantine is agreed officially as a therapeutic drug for moderate-to-severe Alzheimer's disease (AD) in EU and USA. Memantine is a similar uncompetitive NMDA-receptor antagonist to MK-801 and phencyclidine (PCP), and it prevents nerve cell death induced by the ischemia which induces as excessive release of glutamate. These medicines act on an ion channel binding site similar to the magnesium ion binding site. However, MK-801 and PCP cause schizophrenic symptoms, so they are not being used as a therapeutic drug for AD. Memantine does not have those toxicities and does not stimulate acetylcholine release in the cerebral cortex. Although the mechanism of the difference from memantine and MK-801 has not been made clear yet, it seems that memantine is combined and released with the ion channel depending on electric potential in the same way as the magnesium ion. Basic and clinical research will clarify the control mechanism of memantine.

Inhibitory effects of memantine on human cytochrome P450 activities: prediction of in vivo drug interactions

OBJECTIVE

The aim of the present study was to predict the drug interaction potential of memantine by elucidation of its inhibitory effects on cytochrome P450 enzymes using pooled human liver microsomes (HLM) and recombinant P450s.

METHODS

The inhibitory potency of memantine on CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 activities was examined with specific probe drugs in HLM and recombinant P450s. The in vivo drug interactions of memantine were predicted in vitro using the [ I]/([ I] + KI) values.

RESULTS

In HLM, memantine inhibited CYP2B6 and CYP2D6 activities, with KI (IC50) values of 76.7 (279.7) and 94.9 (368.7) microM, respectively. Both inhibitions were competitive. In addition, cDNA-expressed P450s were used to confirm these results. Memantine strongly inhibited recombinant CYP2B6 activity with IC50 ( KI) value of 1.12 (0.51) microM and activity of recombinant CYP2D6 with IC50 (KI) value of 242.4 (84.4) microM. With concentrations up to 1,000 microM, memantine showed no appreciable effect on CYP1A2, CYP2E1, CYP2C9, or CYP3A4 activities and a slight decrease of CYP2A6 and CYP2C19 activities. Based on [ I]/([ I] + KI) values calculated using peak total plasma concentration (or enzyme-available concentration in the liver) of memantine and the KI obtained in HLM, 1.3 (13.5), and 1.0% (11.2%), inhibition of the clearance of CYP2B6 and CYP2D6 substrates could be expected, respectively. Nevertheless, when considering KI values obtained from cDNA-expressed CYP2B6, as generally recommended, even 66.2% (95.9%) decrease in metabolism of coadministered CYP2B6 substrates could be anticipated.

CONCLUSION

Memantine exerts selective inhibition of CYP2B6 activity at clinically relevant concentrations, suggesting the potential for clinically significant drug interactions. Inhibition of other CYPs during memantine therapy is unlikely. Moreover, memantine represents a new, potent, selective inhibitor of recombinant CYP2B6, which may prove useful for screening purposes during early phases of in vitro drug metabolism studies with new chemical entities.

Why do many NMDA antagonists fail, while others are safe and effective at blocking excitotoxicity associated with dementia and acute injury?

Similar to drug development programs for stroke and traumatic brain injury, programs developed for Alzheimer's disease (AD) have not been very effective in treating dementia. Recently, researchers have explored modulating excitatory synaptic neurotransmission via the N-methyl-D-aspartate receptor (NMDAR) to treat AD. However, many investigators doubt that NMDA antagonists are safe and effective for treating persons with AD because they have failed in stroke and trauma programs. This article explores the role of NMDA-mediated excitotoxicity in AD, reviews how the NMDAR functions, highlights the side effects and alternate signaling pathways that are initiated from NMDAR activation, provides examples of NMDA antagonists that do not exhibit the typical side effects, and discusses why some NMDA antagonist compounds are effective and safe in limiting cascades of excitotoxicity in dementia or acute brain injury.

Interrupting apoptosis in neurodegenerative disease: potential for effective therapy?

Current treatment options for neurodegenerative diseases are limited and mainly affect only the symptoms of disease. Because of the unknown and probably multiple causes of these diseases, they cannot be readily targeted. However, it has been established that apoptosis contributes to neuronal loss in most neurodegenerative diseases. A possible treatment option is to interrupt the signaling networks that link neuronal damage to apoptotic degradation in neurodegeneration. The viability of this option depends upon the extent to which apoptosis accounts for neuron loss, whether or not interruption of apoptosis signaling results in recovery of neurological function and whether or not there are significant downsides to targeting apoptosis. Several compounds acting at different sites in known apoptotic signaling networks are currently in development and a few are in clinical trial. If an apoptosis-targeted compound succeeds in slowing or halting neurological dysfunction in one or more neurodegenerative diseases, a new era in the treatment of neurodegenerative diseases will begin.

The glutamatergic system and Alzheimer's disease: therapeutic implications

Alzheimer's disease affects nearly 5 million Americans currently and, as a result of the baby boomer cohort, is predicted to affect 14 million Americans and 22 million persons totally worldwide in just a few decades. Alzheimer's disease is present in nearly half of individuals aged 85 years. The main symptom of Alzheimer's disease is a gradual loss of cognitive function. Glutamatergic neurotransmission, an important process in learning and memory, is severely disrupted in patients with Alzheimer's disease. Loss of glutamatergic function in Alzheimer's disease may be related to the increase in oxidative stress associated with the amyloid beta-peptide that is found in the brains of individuals who have the disease. Therefore, therapeutic strategies directed at the glutamatergic system may hold promise. Therapies addressing oxidative stress induced by hyperactivity of glutamate receptors include supplementation with estrogen and antioxidants such as tocopherol (vitamin E) and acetylcysteine (N-acetylcysteine). Therapy for hypoactivity of glutamate receptors is aimed at inducing the NMDA receptor with glycine and cycloserine (D-cycloserine). Recently, memantine, an NMDA receptor antagonist that addresses the hyperactivity of these receptors, has been approved in some countries for use in Alzheimer's disease.

Memantine (Ebixa®) in the later stages of dementia

Memantine is the first agent licensed for the treatment of moderate to severe Alzheimer's disease. It is an N-methyl D-aspartate (NMDA) receptor antagonist which reduces glutamatergic excitotoxicity. Benefits are seen in cognitive, functional and global measures in both outpatients and nursing home residents. Prospective health economic benefits have been reported.