Maximum tolerated dose and pharmacodynamics of eptastigmine in elderly healthy volunteers

Features and outcomes of drugs for combination therapy as multi-targets strategy to combat Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease (AD), a deleterious neurodegenerative disorder that impairs memory, cognitive functions and may lead to dementia in late stage of life. The pathogenic cause of AD remains incompletely understood and FDA approved drugs are partial inhibitors rather than curative. Most of drugs are synthetic or natural products as galanthamine is an alkaloid obtained from Galanthus spp. Huperzine A, an alkaloid found in Huperzia spp., gingkolides a diterpenoids from Gingko biloba and many ethnobotanicals like Withania somnifera (L.) Dunal., Physostigma venenosum Balf., Bacopa monnieri (L.) Wettst., Centella asiatica (L.) Urb. have been used by traditional Indian, Chinese, and European system of medicines in AD. Clinical significance opioid alkaloid in Papaver somniferum has shown another dimension to this study. Over exploitation of medicinal plants with limited bioactive principles has provided templates to design synthetic drugs in AD e.g. rivastigmine, phenserine, eptastigmine based on chemical structure of physostigmine of Physostigma venenosum Balf. Even ZT-1 a prodrug of Hup A and memogain a prodrug of galantamine has achieved new direction in drug development in AD. All these first-line cholinesterase-inhibitors are used as symptomatic treatments in AD. Single modality of "One-molecule-one-target" strategy for treating AD has failed and so future therapies on "Combination-drugs-multi-targets" strategy (CDMT) will need to address multiple aspects to block the progression of pathogenesis of AD. Besides, cholinergic and amyloid drugs, in this article we summarize proteinopathy-based drugs as AD therapeutics from a variety of biological sources. In this review, an attempt has been made to elucidate the molecular mode of action of various plant products, and synthetic drugs investigated in various preclinical and clinical tests in AD. It also discusses current attempts to formulate a comprehensive CDMT strategy to counter complex pathogenesis in AD.

MATERIALS AND METHODS

Information were collected from classical books on medicinal plants, pharmacopoeias and scientific databases like PubMed, Scopus, GoogleScholar, Web of Science and electronic searches were performed using Cochrane Library, Medline and EMBASE. Also published scientific literatures from Elsevier, Taylor and Francis, Springer, ACS, Wiley publishers and reports by government bodies and documentations were assessed.

RESULTS

60 no. of natural and synthetic drugs have been studied with their significant bioactivities. A decision matrix designed for evaluation of drugs for considering to the hypothetic "CDMT" strategy in AD. We have introduced the scoring pattern of individual drugs and based on scoring pattern, drugs that fall within the scoring range of 18-25 are considered in the proposed CDMT. It also highlights the importance of available natural products and in future those drugs may be considered in CDMT along with the qualified synthetic drugs.

CONCLUSION

A successful validation of the CDMT strategy may open up a debate on health care reform to explore other possibilities of combination therapy. In doing so, it should focus on clinical and molecular relationships between AD and CDMT. A better understanding of these relationships could inform and impact future development of AD-directed treatment strategies. This strategy also involves in reducing costs in treatment phases which will be affordable to a common man suffering from AD.

Fatty Acid Amide Hydrolase (FAAH), Acetylcholinesterase (AChE), and Butyrylcholinesterase (BuChE): Networked Targets for the Development of Carbamates as Potential Anti-Alzheimer's Disease Agents

The modulation of the endocannabinoid system is emerging as a viable avenue for the treatment of neurodegeneration, being involved in neuroprotective and anti-inflammatory processes. In particular, indirectly enhancing endocannabinoid signaling to therapeutic levels through FAAH inhibition might be beneficial for neurodegenerative disorders such as Alzheimer's disease, effectively preventing or slowing the progression of the disease. Hence, in the search for a more effective treatment for Alzheimer's disease, in this paper, the multitarget-directed ligand paradigm was applied to the design of carbamates able to simultaneously target the recently proposed endocannabinoid system and the classic cholinesterase system, and achieve effective dual FAAH/cholinesterase inhibitors. Among the two series of synthesized compounds, while some derivatives proved to be extremely potent on a single target, compounds 9 and 19 were identified as effective dual FAAH/ChE inhibitors, with well-balanced nanomolar activities. Thus, 9 and 19 might be considered as new promising candidates for Alzheimer's disease treatment.

Anticholinesterase-induced symptoms improved by pacemaker implantation in patients with Alzheimer's disease: analysis of 6 cases

Herein we describe 6 cases of patients with Alzheimer's disease presented with syncope, dizziness, and dyspnea soon after the initiation of cholinesterase inhibitor therapy. All patients had bradyarrhythmia on electrocardiogram (ECG). Two patients had complete atrioventricular block, 2 pateints had 2/1 type atrioventricular block, 1 patient had sinus bradycardia and hypersensitive carotid sinus syndrome, and 1 had sick sinus syndrome. All these patients were treated with pacemaker implantation and the cholinesterase inhibitor therapy continued. At 13-month follow-up, no syncope, dizziness, or dyspnea was reported.

Long-acting anticholinesterases for myasthenia gravis: synthesis and activities of quaternary phenylcarbamates of neostigmine, pyridostigmine and physostigmine

The N-monophenylcarbamate analogues of neostigmine methyl sulfate (6) and pyridostigmine bromide (8) together with their precursors (5), (7), and the N(1)-methylammonium analogues of (-)-phenserine (12), (-)-tolserine (14), (-)-cymserine (16) and (-)-phenethylcymserine (18) were synthesized to produce long-acting peripheral inhibitors of acetylcholinesterase or butyrylcholinesterase. Evaluation of their cholinesterase inhibition against human enzyme ex vivo demonstrated that, whereas compounds 5-8 possessed only marginal activity, 12, 14, 16 and 18 proved to be potent anticholinesterases. An extended duration of cholinesterase inhibition was determined in rodent, making them of potential interest as long-acting agents for myasthenia gravis.

Cardiovascular effects and risk of syncope related to donepezil in patients with Alzheimer's disease

BACKGROUND

When otherwise unexplained, syncope in patients with Alzheimer's disease may be attributed to bradycardia caused by cholinesterase inhibitors. We studied prospectively the clinical events and cardiovascular changes occurring during treatment with donepezil in patients with Alzheimer's disease.

METHODS

Consecutive patients presenting with mild-to-moderate Alzheimer's disease were included in the study. Their clinical characteristics, blood pressure, heart rate and electrocardiogram were recorded before (baseline) and during treatment with donepezil. The drug was administered at a dosage of 5 mg/day for 1 month and 10 mg/day for the following 7 months, as tolerated. We compared the baseline observations with those made at 1, 2 and 8 months of donepezil treatment. We also examined the effects of negatively chronotropic or dromotropic drugs concomitantly administered with donepezil.

RESULTS

Thirty patients were included in the study, of whom 43% were taking negatively chronotropic or dromotropic drugs. The first month of therapy (donepezil 5 mg/day) was completed by 26 patients. During the 7-month high-dosage phase (10 mg/day), four patients dropped out of the study; thus, 22 patients completed the full 8 months of the study. The mean heart rate was 66 +/- 8 beats/min at baseline in the overall study population. This decreased significantly to 62 +/- 9, 61 +/- 7 and 62 +/- 8 beats/min at the 1, 2 and 8 month timepoints, respectively (all p = 0.002 vs baseline). Among patients not receiving negatively chronotropic or dromotropic drugs, heart rate decreased significantly over the course of the study (from 67 +/- 8 beats/min at baseline to 62 +/- 8 beats/min at 1 month, 62 +/- 7 beats/min at 2 months and 62 +/- 8 beats/min at 8 months [all p = 0.005 vs baseline]). There was no significant change in heart rate in patients who were receiving negatively chronotropic or dromotropic drugs. The PR interval increased over the course of the study in all patient groups, but these changes were only statistically significant in the group of patients who were not taking negatively chronotropic or dromotropic drugs (155 +/- 23ms at baseline vs 158 +/- 21, 160 +/- 22 and 163 +/- 24ms at the 1, 2 and 8 month timepoints; all p = 0.02 vs baseline). One patient developed syncope due to orthostatic hypotension; there were no cases of bradycardia-induced syncope. Gastrointestinal manifestations were reported in ten of the study patients. Abdominal pain and vomiting were the reasons for study termination in five of the eight patients who did not complete the trial.

CONCLUSION

A donepezil-induced decrease in heart rate and increase in PR interval were observed only in patients with Alzheimer's disease who were not treated with negatively chronotropic or dromotropic drugs. These changes were not associated with bradycardia-induced syncope.

Causes of syncope in patients with Alzheimer's disease treated with donepezil

INTRODUCTION

Treatment of Alzheimer's disease (AD) with cholinesterase inhibitors carries a theoretical risk of precipitating bradycardia. Though syncope occurs in patients with AD, its aetiology is unclear. The aim of this study was to determine the causes of syncope in patients with AD who were treated with donepezil and hospitalised for evaluation of syncope.

METHODS

We studied 16 consecutive patients (12 women, 4 men) with AD aged 80 +/- 4 years who were hospitalised for evaluation of syncope. All patients underwent staged evaluation, ranging from physical examination to electrophysiological testing.

RESULTS

The mean dose of donepezil administered was 7.8 mg/day, and the mean duration of donepezil treatment at the time of syncope was 12 +/- 8 months. A cause of syncope was identified in 69% of patients. Carotid sinus syndrome was observed in three patients, complete atrioventricular block in two patients, sinus node dysfunction in two patients, severe orthostatic hypotension in two patients and paroxysmal atrial fibrillation in one patient. A brain tumour was discovered in one patient. No cause of syncope was found in 31% of patients despite comprehensive investigation. Repetition of the investigations after discontinuation of donepezil was noncontributory.

CONCLUSION

In patients with AD treated with donepezil, a noninvasive evaluation identified a probable cause of syncope in over two-thirds of patients. Cardiovascular abnormalities were predominant. Noninvasive evaluation is recommended before discontinuing treatment with cholinesterase inhibitors in patients with AD and unexplained syncope.

Clinical pharmacokinetics and pharmacodynamics of cholinesterase inhibitors

Cholinesterase inhibitors are the 'first-line' agents in the treatment of Alzheimer's disease. This article presents the latest information on their pharmacokinetic properties and pharmacodynamic activity. Tacrine was the first cholinesterase inhibitor approved by regulatory agencies, followed by donepezil, rivastigmine and recently galantamine. With the exception of low doses of tacrine, the cholinesterase inhibitors exhibit a linear relationship between dose and area under the plasma concentration-time curve. Cholinesterase inhibitors are rapidly absorbed through the gastrointestinal tract, with time to peak concentration usually less than 2 hours; donepezil has the longest absorption time of 3 to 5 hours. Donepezil and tacrine are highly protein bound, whereas protein binding of rivastigmine and galantamine is less than 40%. Tacrine is metabolised by hepatic cytochrome P450 (CYP) 1A2, and donepezil and galantamine are metabolised by CYP3A4 and CYP2D6. Rivastigmine is metabolised by sulfate conjugation. Two cholinesterase enzymes are present in the body, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Tacrine and rivastigmine inhibit both enzymes, whereas donepezil and galantamine specifically inhibit AChE. Galantamine also modulates nicotine receptors, thereby enhancing acetylcholinergic activity at the synapse. These different pharmacological profiles provide distinctions between these agents. Cholinesterase inhibitors show a nonlinear relationship between dose and cholinesterase inhibition, where a plateau effect occurs. Cholinesterase inhibitors display a different profile as each agent achieves its plateau at different doses. In clinical trials, cholinesterase inhibitors demonstrate a dose-dependent effect on cognition and functional activities. Improvement in behavioural symptoms also occurs, but without a dose-response relationship. Gastrointestinal adverse events are dose-related. Clinical improvement occurs with between 40 and 70% inhibition of cholinesterase. A conceptual model for cholinesterase inhibitors has been proposed, linking enzyme inhibition, clinical efficacy and adverse effects. Currently, measurement of enzyme inhibition is used as the biomarker for cholinesterase inhibitors. New approaches to determining the efficacy of cholinesterase inhibitors in the brain could involve the use of various imaging techniques. The knowledge base for the pharmacokinetics and pharmacodynamics of cholinesterase inhibitors continues to expand. The increased information available to clinicians can optimise the use of these agents in the management of patients with Alzheimer's disease.

Eptastigmine: ten years of pharmacology, toxicology, pharmacokinetic, and clinical studies

Eptastigmine (heptyl-physostigmine tartrate) is a carbamate derivative of physostigmine in which the carbamoylmethyl group in position 5 of the side chain has been substituted with a carbamoylheptyl group. In vitro and ex vivo results suggest that eptastigmine has a long-lasting reversible brain cholinesterase (i.e., acetylcholinesterase and butyryl-cholinesterase) inhibitory effect. When administered in vivo to rodents by various routes, eptastigmine inhibits cerebral acetylcholinesterases (AChE) and increases acetylcholine (Ach) brain levels by 2500-3000%, depending on the dose. This effect leads to an improvement in the cerebral blood flow in the ischemic brain, excitatory and inhibitory effects on the gastrointestinal tract and to a protection from acute soman and diisopropylfluorophosphate intoxication. Eptastigmine, by either acute or chronic administration, has been found to have memory enhancing effects in different species of normal, aged and lesioned animals. It also restored to normal the age-related increase of EEG power without affecting spontaneous motor activity. Clinical investigations on more than 1500 patients with Alzheimer's disease demonstrated that eptastigmine significantly improved cognitive performance (as assessed by the cognitive subscale of the Alzheimer's Disease Assessment Scale) as compared with placebo. This improvement was most evident in patients with more severe cognitive impairment at the baseline. The relationship between patient performance and average steady-state AChE inhibition was described by an inverted U-shaped dose-response curve. Pharmacokinetic studies have revealed that after oral administration eptastigmine is rapidly distributed to the tissues and readily enters the CNS, where it can be expected to inhibit AChE for a prolonged period. Eptastigmine is generally well tolerated and the majority of adverse events (cholinergic) were mild to moderate in intensity. However, the adverse hematologic (granulocytopenia) effects reported in two studies have resulted in the suspension of further clinical trials.

RBC cholinesterase inhibition: a useful surrogate marker for cholinesterase inhibitor activity in Alzheimer disease therapy?

Red blood cell (RBC) acetylcholinesterase (AChE) inhibition has been used as a peripheral surrogate marker for the activity of centrally acting AChE inhibitors (AChEIs) in the treatment of Alzheimer disease. As a valid peripheral surrogate marker, RBC AChE inhibition should reflect the central pharmacodynamic activity of the compound and should demonstrate a relation with cognitive or global improvement in patients with Alzheimer disease. As a useful clinical tool, RBC AChE inhibition should also provide an advantage in dose optimization. However, the application of surrogate markers in research and clinical use is controversial (Prentice, 1989; Gotzsche, 1996; Colburn, 1997; De Gruttola et al., 1997). For instance, surrogate markers that have been identified or applied inappropriately can lead to erroneous conclusions, slowing the drug development process (Colburn, 1997). Also, the validation of surrogate markers for the pharmacodynamic activity of central nervous system drugs is not always possible because samples of brain tissue cannot be analyzed in humans. Finally, although validation of peripheral markers for central nervous system drugs has been approached via analysis of cerebrospinal fluid (Cutler et al., 1998a), few markers have been subjected to such rigorous evaluation in clinical studies. The extent to which measures of peripheral AChE inhibition accurately model central drug activity and therapeutic effectiveness of AChEIs, both as individual agents and as a drug class, is the focus of this review. AChEIs comprise a group of structurally diverse compounds with a wide range of relative specificities for the various molecular species of cholinesterase found in plasma, RBCs, and the brain. Studies of RBC AChE inhibition after administration of AChEIs in animals are of limited utility because of the differential sensitivity of AChEIs for human versus animal forms of AChE, the poor correlation between effective doses in animals and humans, and the lack of standardized measurements of effectiveness. Although clinical studies of donepezil, metrifonate, and eptastigmine have suggested the potential use of RBC AChE inhibition as a predictor of clinical response, the degree of inhibition yielding maximum cognitive improvements was highly variable from compound to compound (30-80%). Further, investigators did not prove a relation between central and peripheral pharmacodynamics or demonstrate an advantage over dose in the ability of RBC AChE inhibition to predict clinical response. A study of rivastigmine in patients with Alzheimer disease revealed that cerebrospinal fluid AChE inhibition correlated well with cognitive performance, whereas peripheral inhibition did not. Therefore, RBC cholinesterase inhibition is not a reliable surrogate marker for the activity of AChEIs as a class of drugs, and its usefulness as a dose optimization tool for individual agents has yet to be demonstrated clearly.

Clinical pharmacology of psychotropic drugs

No Abstract

Cholinesterase inhibitors for the treatment of Alzheimer's disease in the elderly

The treatment of Alzheimer's disease is of increasing importance as the population ages and the number of people with the disease increases. The aetiology of Alzheimer's disease is complex and therefore treatment strategies rely on generalised pathological findings. Cholinesterase inhibitors enhance a generalised deficit of central nervous system acetylcholine and are the first class of agents specifically approved for the treatment of Alzheimer's disease. The clinical efficacy of the different cholinesterase inhibitors is similar; however, differences in pharmacodynamic and pharmacokinetic parameters can influence tolerability and safety in the elderly population. Concomitant disease states, significant drug interactions and the altered kinetics and dynamics seen in elderly patients can also affect treatment outcome. Although cholinesterase inhibitors are not 'curative' for Alzheimer's disease, clinical evidence indicates that these drugs can significantly delay the progress of cognitive impairment. Consequently, they represent a useful treatment for the symptoms of Alzheimer's disease in the elderly.

Efficacy and safety of eptastigmine for the treatment of patients with Alzheimer's disease

OBJECTIVE

To evaluate the efficacy and safety of eptastigmine in patients with moderate to moderately severe AD.

BACKGROUND

Eptastigmine is a centrally acting cholinesterase inhibitor.

METHODS

The study was carried out according a multicenter, randomized, double-blinded, placebo-controlled, parallel-group design. Patients received a 24-week treatment with placebo or eptastigmine 15 mg or 20 mg three times daily after a 4-week, stepwise dose escalation. The effects of treatment on cognition, global function, and activities of daily living were evaluated with the Alzheimer's Disease Assessment Cognitive Subscale (ADAS-Cog), the Clinician's Interview-Based Impression of Change Plus (CIBIC-Plus), and the Instrumental Activities of Daily Living scale (IADL), respectively.

RESULTS

Thirty-six centers recruited 491 patients: 164 on placebo, 166 on eptastigmine 15 mg three times daily, and 161 on eptastigmine 20 mg three times daily. Percentages of patients completing double-blinded treatment were 87% in the placebo group and 86% in both the eptastigmine-treated groups. At the end of treatment, the intent-to-treat analysis on 463 patients showed a dose-dependent effect of eptastigmine on all efficacy variables, with a statistically significant effect of the 20 mg three times daily dose compared with placebo on the ADAS-Cog, CIBIC-Plus, and IADL. Patients on eptastigmine 15 mg three times daily performed significantly better than placebo-treated patients only on the ADAS-Cog. Eleven patients on placebo (7%), 13 patients on eptastigmine 15 mg three times daily (8%), and 12 patients on eptastigmine 20 mg three times daily (8%) discontinued study treatment because of adverse events. Adverse events were recorded in 49% of patients on placebo compared with 54% on eptastigmine 15 mg three times daily and 48% on eptastigmine 20 mg three times daily. Cholinergic side effects (nausea, vomiting, diarrhea, and abdominal pain) were reported with similar frequency in the eptastigmine- and placebo-treated patients. There was a dose-dependent transient and mild neutropenic effect associated with eptastigmine treatment, and one patient on 20 mg three times daily had an asymptomatic pancytopenia.

CONCLUSIONS

Eptastigmine produces significant cognitive, clinical, and functional benefits in patients with probable AD. Although the cholinergic tolerability of eptastigmine was found to be favorable, its potential adverse hematologic effects limit its clinical utility.