Alzheimer's disease: beware of interactions with cholinesterase inhibitors

(1) Cholinesterase inhibitors such as donepezil, galantamine and rivastigmine, are not very effective in slowing the cognitive decline associated with Alzheimer's disease. Memantine, which is no more effective, has dopaminergic and atropinic effects but is not a cholinesterase inhibitor. (2) Cholinesterase inhibitors have mainly cholinergic adverse effects, causing gastrointestinal, neurological, cardiovascular and urinary disorders (incontinence). (3) Increased mortality, mainly due to cardiovascular events, was observed in placebo-controlled trials of galantamine. In one trial there were more deaths in patients on donepezil than on placebo. (4) Atropinic drugs tend to aggravate cognitive disorders that are treated with cholinesterase inhibitors. (5) Cholinesterase inhibitor + neuroleptic combinations are associated with an increased risk of extrapyramidal adverse effects. An increase in mortality was reported during trials of neuroleptics involving patients with dementia, and also during trials of cholinesterase inhibitors. (6) Combining cholinesterase inhibitors with drugs that reduce the heart rate, depress cardiac conduction, or induce torsades de pointes increases the risk of arrhythmias and cardiac conduction disorders. (7) Donepezil and galantamine are metabolised by cytochrome P450 isoenzymes 3A4 and 2D6, creating a strong potential for pharmacokinetic interactions with inhibitors and inducers of these isoenzymes. Rivastigmine is mainly metabolised by cholinesterases, and binds poorly to cytochrome P450 isoenzymes. (8) Cholinesterase inhibitors inhibit the metabolism of suxamethonium and thereby augment and prolong the neuromuscular blockade induced by this curare. (9) In practice, caregivers should be aware of the potential adverse effects of cholinesterase inhibitors, which often resemble symptoms of Alzheimer's disease and may be due to drug-drug interactions or to antagonist effects with other drugs, such as those with atropinic effects. Additionally, the many adverse effects associated with the use of cholinesterase inhibitors highlights the need for regular re-evaluation of the use of these medicines and of the balance of benefit versus risk in individual patients.     

Pharmacodynamic-tolerability relationships of cholinesterase inhibitors for Alzheimer's disease

According to the cholinergic hypothesis, the impairment of cognitive function and the behavioural disturbances that affect patients with Alzheimer's disease are mainly due to cortical deficiencies in cholinergic transmission. Numerous cholinesterase inhibitors have been investigated for treatment of this disease, the rationale being to support the cholinergic system by blocking the degradation of acetylcholine released from presynaptic neurons. These drugs can be classified as reversible (tacrine, donepezil and galantamine), pseudo-reversible (physostigmine, eptastigmine and rivastigmine) or irreversible (metrifonate) enzyme inhibitors. This article reviews efficacy and tolerability results from 6-month placebo-controlled studies of 7 cholinesterase inhibitors: tacrine (80 to 160 mg/day), donepezil (5 to 10 mg/day), rivastigmine (1 to 12 mg/day), metrifonate (30 to 80 mg/day), eptastigmine (30 to 60 mg/day), physostigmine (30 to 36 mg/day) and galantamine (8 to 32 mg/day). All these agents have demonstrated a statistically significant, although modest, effect versus placebo on the cognitive and global performance of patients with Alzheimer's disease. Dramatic clinical response has been seen in only 3 to 5% of patients. There are no major differences in terms of efficacy between the different drugs. The mean difference between drug and placebo effects on standardised psychometric scales is about 2 to 4 points on the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog; a 70-point cognitive scale) and 0.2 to 0.5 points on the Clinician's Interview-Based Impression of Change with Caregiver Input (CIBIC-Plus; a 7-point global scale), or 5 to 14% of the average value of the scales. The most common adverse effects observed after administration of cholinesterase inhibitors are nausea, vomiting, diarrhoea, dizziness, asthenia and anorexia, all symptoms linked to cholinergic overstimulation. These effects are dose related and largely depend on the degree of cholinesterase inhibition. Also important is the rate of onset of cholinesterase inhibition, which depends on the kinetics of enzyme inhibition, the presence and rate of titration, and the pharmacodynamic peak-to-trough fluctuations. A model predicting the incidence of nausea based on acetylcholinesterase inhibition and the half-life of acetylcholinesterase recovery is proposed. In conclusion, cholinesterase inhibitors are the only pharmacological agents proved to be effective for the treatment of Alzheimer's disease in large, long term, double-blind, placebo-controlled trials. While the efficacy of different cholinesterase inhibitors is similar, their tolerability profiles differ. For example, the incidence of nausea (in excess of that seen with placebo) at cognitively effective dosages ranges from 1% with eptastigmine 60 mg/day to 53% with physostigmine 30 mg/day. Differences in tolerability profile may be due to the extent of peripheral acetylcholinesterase inhibition needed to reach clinical efficacy. Other contributing pharmacodynamic factors are the rate of onset of and fluctuations in acetylcholinesterase inhibition at steady state.     

Pharmacoeconomics of cholinesterase inhibitors in the treatment of Alzheimer's disease

Cholinesterase inhibitors constitute one of few treatment options available for Alzheimer's disease, the most common cause of dementia. The modest effects and relatively high acquisition costs of these drugs make the health economics of dementia an important subject of study. Simulation models can be used to bring together existing data and make predictions of the long-term cost effectiveness of treatment. Most models have been built around cognitive function as a key parameter based on the observed relationship between cognitive function and costs of care. Patients with more severe disease attain higher total costs of care. Also, these patients have a higher share of formal care costs than do patients with mild disease, who are usually looked after by informal caregivers. The valuation of unpaid care is controversial, and the choice of method may affect results considerably. Another important issue is the measurement of health-related QOL in patients with Alzheimer's disease. The few existing studies have used proxy respondents to elicit utility weights in different disease states; however, this methodology has not been validated. It is likely that the increased drug costs incurred by the use of cholinesterase inhibitors will be offset (at least partly) by savings in other healthcare costs. However, these results should be viewed as preliminary, since we are still awaiting data from long-term follow-up studies. Also, the value of treatment for patients and caregivers in terms of QOL improvements has yet to be established.     

Strategies for continued successful treatment of Alzheimer's disease: switching cholinesterase inhibitors

SUMMARY

Cholinesterase (ChE) inhibitors represent the standard therapeutic approach to the treatment of Alzheimer's disease (AD). However, a proportion of patients experience lack or loss of therapeutic benefit with an initial agent, or discontinue due to safety/tolerability issues. In many instances, no alternative treatment is offered once the initial agent has been stopped. Thus, for many patients, the total duration of treatment is relatively short in comparison with the chronic nature of AD.

Switching medications is a common therapeutic strategy within many drug classes across many clinical areas following a lack/loss of efficacy or safety/tolerability problems, and is also an increasingly important concept in the management of AD with ChE inhibitors. A number of open-label studies, where patients were switched from donepezil to rivastigmine, have indicated that

approximately 50% of patients experiencing a lack/loss of efficacy with donepezil (a selective acetylcholinesterase [AChE] inhibitor) respond to subsequent treatment with rivastigmine (a dual AChE and butyrylcholinesterase inhibitor). In these studies, rivastigmine was well tolerated, and the occurrence of safety/tolerability problems with donepezil was not predictive of similar problems with rivastigmine.

In the summer of 2002, leading neurologists and psychiatrists attended a medical experts meeting to discuss the clinical importance of switching ChE inhibitors in AD. The expert panel examined available clinical data, shared clinical experiences, and discussed current clinical guidelines for switching. The panel also aimed to reach consensus on 'whom to switch', 'when to switch' and 'how to switch'. The key findings from that meeting are reported in this review.     

Strategies for continued successful treatment of Alzheimer's disease: switching cholinesterase inhibitors

Cholinesterase (ChE) inhibitors represent the standard therapeutic approach to the treatment of Alzheimer's disease (AD). However, a proportion of patients experience lack or loss of therapeutic benefit with an initial agent, or discontinue due to safety/tolerability issues. In many instances, no alternative treatment is offered once the initial agent has been stopped. Thus, for many patients, the total duration of treatment is relatively short in comparison with the chronic nature of AD. Switching medications is a common therapeutic strategy within many drug classes across many clinical areas following a lack/loss of efficacy or safety/tolerability problems, and is also an increasingly important concept in the management of AD with ChE inhibitors. A number of open-label studies, where patients were switched from donepezil to rivastigmine, have indicated that approximately 50% of patients experiencing a lack/loss of efficacy with donepezil (a selective acetylcholinesterase [AChE] inhibitor) respond to subsequent treatment with rivastigmine (a dual AChE and butyrylcholinesterase inhibitor). In these studies, rivastigmine was well tolerated, and the occurrence of safety/tolerability problems with donepezil was not predictive of similar problems with rivastigmine. In the summer of 2002, leading neurologists and psychiatrists attended a medical experts meeting to discuss the clinical importance of switching ChE inhibitors in AD. The expert panel examined available clinical data, shared clinical experiences, and discussed current clinical guidelines for switching. The panel also aimed to reach consensus on 'whom to switch', 'when to switch' and 'how to switch'. The key findings from that meeting are reported in this review.     

Modelling the cost effectiveness of cholinesterase inhibitors in the management of mild to moderately severe Alzheimer's disease

OBJECTIVE: To estimate the cost effectiveness (from the UK NHS and personal social services perspective) of the cholinesterase inhibitors donepezil, rivastigmine and galantamine compared with usual care in the treatment of mild to moderately severe Alzheimer's disease. Patients had a mean age of 74 years, a mean disease duration of 1 year and a mean Alzheimer's disease assessment scale-cognitive subscale score of 24. METHODS: A pharmacoeconomic model was used to predict long-term outcomes over a 5-year time horizon and to estimate the cost effectiveness of cholinesterase inhibitors for the management of Alzheimer's disease. The model structure is informed by a systematic review of the literature on the clinical and cost effectiveness of cholinesterase inhibitors and a review of the literature on the costs and outcomes associated with treatment for Alzheimer's disease. The main outcome measure used was the cost per quality-adjusted life-year (QALY) gained. All healthcare costs (excluding cholinesterase inhibitor costs) were indexed to pounds sterling (2003 values). Drug costs are 2005 values. Multivariate probabilistic sensitivity analysis and scenario analysis were undertaken to assess uncertainty in the results. RESULTS: The clinical benefits on cognition from treatment with cholinesterase inhibitors resulted in an incremental cost per QALY gained ranging from 53,780 pounds sterling to 74,735 pounds sterling, over 5 years (vs usual care). Uncertainty analysis suggests that the probability of any of these treatments having an incremental cost per QALY of < 30,000 pounds sterling is < 21%. The key determinants of cost effectiveness were the effectiveness of treatment, the mean treatment cost and the cost savings associated with an expected delay in disease progression. CONCLUSIONS: Results presented in this paper suggest that the use of cholinesterase inhibitors may not be a cost-effective use of NHS resources. Guidance from the National Institute for Health and Clinical Effectiveness (NICE) in the UK on their judgements surrounding the acceptability of technologies as an effective use of resources, indicates there would need to be special reasons for accepting cholinesterase inhibitors as a cost-effective use of NHS resources.     

Effects of cholinesterase inhibitors on behavioural disturbances in Alzheimer's disease: a systematic review

Behavioural disturbances, also termed neuropsychiatric symptoms, are a frequent clinical feature of dementia in Alzheimer's disease (AD). Many AD patients receive treatment with cholinesterase inhibitors (ChEIs). This review examines the evidence for behavioural effects of the four ChEIs that have been approved for the treatment of mild to moderate AD. A systematic search of the MEDLINE and EMBASE databases and the Cochrane Library was conducted to identify clinical trials that had a randomised, placebo-controlled design. Studies were included in this review if they enrolled patients who had received a diagnosis of probable AD, involved at least one ChEI, and used an appropriate instrument for the assessment of behavioural disturbances. Fourteen studies that matched the selection criteria were identified in the literature. A statistically significant difference between active treatment and placebo with regard to behavioural symptoms was observed in three of the 14 studies. Treatment effects varied between 2.0 and 6.2 points on the Neuropsychiatric Inventory. ChEIs have moderate effects when used as a blanket treatment for the cluster of behavioural disturbances in AD. With regard to the limitations of the available trials, and in view of the risks that are associated with the use of atypical antipsychotics, the potential of ChEIs for the management of specific neuropsychiatric symptoms in patients with AD should be explored in further studies.     

Bradycardia due to cholinesterase inhibitors: identify adverse effects and take them into account

The cholinesterase inhibitors donepezil, rivastigmine and galantamine have a modest and transient benefit in Alzheimer's disease. Their known adverse effects include bradycardia. A Canadian case-control study conducted between 2003 and 2008 showed a statistically significant increase in the risk of hospitalisation for bradycardia among patients who had been taking a cholinesterase inhibitor for less than 3 months, compared with patients who had stopped taking a cholinesterase inhibitor more than 6 months previously. After hospital discharge, more than half of these patients were again prescribed a cholinesterase inhibitor, and 4% of them were re-admitted for bradycardia. In practice, when an adverse effect has been identified and treated, this information must be shared and taken into account by all those involved in the patient's subsequent management.     

Cholinergic therapies for Alzheimer's disease: progress and prospects

Cholinomimetic drugs are now available to treat the cognitive impairments associated with Alzheimer's disease (AD), although evidence indicates that the effects of acetylcholinesterase (AChE) inhibitors on measures of cognitive function may be secondary to an action on attentional mechanisms. There is also convincing evidence suggesting that cholinomimetic drugs (e.g., AChE inhibitors and agents acting on cholinergic receptors) will have utility in the treatment of other, non-cognitive changes in behavior that are often associated with AD. This review describes some of the approaches to cholinergic therapy and considers the symptoms that are best suited to these treatment modalities.     

Cholinergic drugs in pharmacotherapy of Alzheimer's disease

The cholinergic hypothesis of Alzheimer's disease has spurred the development of numerous structural classes of compounds with different pharmacological profiles aimed at increasing central cholinergic neurotransmission, thus providing a symptomatic treatment for this disease. Indeed, the only drugs currently approved for the treatment of Alzheimer's disease are cholinomimetics with the pharmacological profile of acetylcholinesterase inhibitors. Recent evidence of a potential disease modifying role of acetylcholinesterase inhibitors and M(1) muscarinic agonists have led to a revival of this approach, which might be considered as more than a symptomatic treatment.     

Novel cholinesterase inhibitors as future effective drugs for the treatment of Alzheimer's disease

Current pharmacotherapy for Alzheimer's disease involves compounds that are aimed at increasing the levels of acetylcholine in the brain by facilitating cholinergic neurotransmission through inhibition of cholinesterase. These drugs, known as acetylcholinesterase inhibitors, have been shown to improve cognition and global functions but have little impact on improving the eventual progression of the disease; however, there is evidence that other cholinesterases such as butyrylcholinesterase can play an important role in cholinergic function in the brain, and the long-suspected non-cholinergic actions of acetylcholinesterase, mainly the interference with the beta-amyloid protein cascade, have recently driven a profound revolution in cholinesterase drug research. Several disease-modifying agents are under development that target these enzymes and have hope of becoming the next generation of effective drugs in the treatment of Alzheimer's disease.     

Cost effectiveness of cholinesterase inhibitors in the treatment of Alzheimer's disease: a review with methodological considerations

Cholinesterase inhibitors have been available for the treatment of Alzheimer's disease since 1993. They have significantly positive effects on cognitive functioning and other domains of functional capacity, such as activities of daily life in terms of efficacy, but the clinical value of these effects are under discussion. Cholinesterase inhibitors may also influence behavioural and psychological symptoms in Alzheimer's disease. Cholinesterase inhibitors are also regarded as rather expensive and, therefore, the question of cost effectiveness is essential. Pharmacoeconomic evaluations of cholinesterase inhibitors have so far been conducted in retrospect on efficacy data from prospective randomised clinical trials combined with economic data from other sources. There are no published specific cost-effectiveness studies of cholinesterase inhibitors which prospectively collected empirical data on costs and outcomes. There is only one published randomised clinical trial with such empirical data with a cost consequence analysis design, indicating cost neutrality. Several types of models to describe the long-term effects have been published, indicating cost effectiveness. However, due to methodological considerations, the validity of these models is difficult to judge. A research agenda for the cost effectiveness of cholinesterase inhibitors is proposed, including long-term studies with empirical data on resource use, costs and outcomes, studies on quality of life, informal care and behavioural and psychological symptoms, combination and comparative studies on mild cognitive impairment.     

Cholinergic targets for cognitive enhancement in schizophrenia: focus on cholinesterase inhibitors and muscarinic agonists

Rationale Alterations in the central cholinergic system of patients with schizophrenia such as reduced numbers of muscarinic and nicotinic receptors in the cortex and hippocampus may contribute to the cognitive impairment of schizophrenia. Therefore, pharmacological treatments that enhance central cholinergic function may be useful as cognitive enhancers in schizophrenia.Methods Searches were conducted for articles which investigated alterations of central cholinergic systems in patients with schizophrenia. Additional searches were conducted for animal and human trials of potential cognitive enhancing compounds that target the cholinergic system and any preliminary trials conducted with schizophrenic patients.Results Currently available treatments which are potentially suitable for this purpose include acetylcholinesterase inhibitors, muscarinic agonists, nicotinic agonists, and allosteric potentiators of nicotinic receptor function. Although some open label studies demonstrate modest cognitive improvements of schizophrenic patients treated with donepezil, data from a blinded, placebo controlled study demonstrate no effect. Data from a controlled trial of galantamine, a combined acetylcholinesterase inhibitor and allosteric potentiator of the nicotinic receptor, indicates that this may be an effective alternative. In addition, some preclinical data indicates that selective M₁ muscarinic agonists under development may have potential as cognitive enhancers and antipsychotic treatments for schizophrenic patients.Conclusions A cholinergic approach to ameliorating the cognitive dysfunction of schizophrenia appears viable. There is some preliminary data to support the efficacy of combined acetylcholinesterase inhibitors and allosteric potentiators of the nicotinic receptor, whereas future trials are awaited for more specific muscarinic agonists currently under development.     

Cholinergic agonists and the treatment of Alzheimer's disease

Over the past decade, considerable effort was focused on the development of muscarinic and nicotinic agonists for the treatment of Alzheimer's disease. The rationale for developing muscarinic agonists was based on the role of acetylcholine in learning and memory function and the consistent neurochemical finding that cholinergic neurons degenerated in Alzheimer's patients. Thus far, the clinical utility of muscarinic agonists remains unproven, yet recent studies suggest that muscarinic agonists might be useful in treating not only memory deficits, but also psychiatric disturbances and some of the underlying causes of Alzheimer's disease, such as the deposition of Abeta. In addition, nicotinic receptors may play a role in cognitive function and help regulate the toxicity of amyloid precursor protein. Ultimately, cholinergic agonists may prove useful in the treatment of Alzheimer's disease.     

Galantamine: new preparation. The fourth cholinesterase inhibitor for Alzheimer's disease

(1) The reference symptomatic treatment for mild to moderate Alzheimer's disease is a cholinesterase inhibitor such as donepezil, but efficacy is only moderate and only about 10% of those patients treated actually benefit. (2) Galantamine is the fourth cholinesterase inhibitor to be marketed in France for Alzheimer's disease. The clinical file contains data from five double-blind placebo-controlled trials lasting 3-6 months, but no data comparing galantamine with other drugs. (3) These trials show that about 5-13% of patients treated with galantamine may be improved. (4) Adverse effects are very frequent, and are similar to those of other cholinesterase inhibitors, i.e. nausea, vomiting, diarrhoea, abdominal pain, dyspepsia, etc. (5) For patients who are eligible for drug therapy, the reference treatment is still donepezil, for want of anything better.     

Long-term cholinesterase inhibitor treatment of Alzheimer's disease

The most prevalent cause of dementia--Alzheimer's disease--is characterised by an early cholinergic deficit that is in part responsible for the cognitive deficits, especially memory and attention defects, seen with this condition. Three cholinesterase inhibitors (ChEIs), namely donepezil, rivastigmine and galantamine, are widely used for the symptomatic treatment of patients with Alzheimer's disease. Placebo-controlled, randomised clinical trials have shown significant effects of these drugs on global function, cognition, activities of daily living (ADL) and behavioural symptoms in patients with this disorder. These trials have been conducted for up to 12 months and were followed by open-label extension studies. One placebo-controlled, randomised clinical trial followed patients for up to 4 years. Both retrospective and prospective follow-up studies suggest a treatment effect for ChEIs that lasts for up to 5 years. Studies have shown comparable effects for ChEIs in patients with moderate-to-severe Alzheimer's disease or mild Alzheimer's disease. Clinically relevant responses consist not only of improvement over 3-6 months but also stabilisation and possibly slower than expected decline. Lack of overt clinical improvement in one domain (e.g. global function, cognition, ADL or behaviour) does not preclude clinically relevant benefit(s) in other domains. If it is judged that the patient has experienced a treatment effect from ChEI therapy during the first 6 months, it is recommended that treatment be continued for at least 1 year before discontinuation is considered again. On average, patients will return to their pre-treatment status between 9 and 12 months of initiation of treatment. However, this return to pre-treatment level does not mean that the treatment effect has disappeared. At this point in time, the patient may still function better than he or she would have without treatment. Setting a fixed measurement, e.g. a Mini-Mental State Examination score, as a 'when to stop treatment limit' is not clinically rational. The length of treatment should depend on several individual patient factors. The earlier the diagnosis is made and the slower the rate of disease progression, the longer the treatment period will tend to be. Treatment duration must therefore be evaluated on an individual basis, and the patient's status compared with what would have been expected without treatment. If a clinical evaluation is conducted with a view to stopping or switching treatment, it is crucial that all domains are evaluated and that the patient is evaluated at more than one point in time before the decision is made.