The effect of multiple doses of donepezil HCl on the pharmacokinetic and pharmacodynamic profile of warfarin

Adverse event profile of memantine and donepezil combination therapy: a real-world pharmacovigilance analysis based on FDA adverse event reporting system (FAERS) data from 2004 to 2023

Background

Donepezil in combination with memantine is a widely used clinical therapy for moderate to severe dementia. However, real-world population data on the long-term safety of donepezil in combination with memantine are incomplete and variable. Therefore, the aim of this study was to analyze the adverse events (AEs) of donepezil in combination with memantine according to US Food and Drug Administration Adverse Event Reporting System (FAERS) data to provide evidence for the safety monitoring of this therapy.

Methods

We retrospectively analyzed reports of AEs associated with the combination of donepezil and memantine from 2004 to 2023 extracted from the FAERS database. Whether there was a significant association between donepezil and memantine combination therapy and AEs was assessed using four disproportionality analysis methods, namely, the reporting odds ratio, proportional reporting ratio, Bayesian confidence propagation neural network, and multi-item gamma Poisson shrinker methods. To further investigate potential safety issues, we also analyzed differences and similarities in the time of onset and incidence of AEs stratified by sex and differences and similarities in the incidence of AEs stratified by age.

Results

Of the 2,400 adverse drug reaction (ADR) reports in which the combination of donepezil and memantine was the primary suspected drug, most of the affected patients were female (54.96%) and older than 65 years of age (79.08%). We identified 22 different system organ classes covering 100 AEs, including some common AEs such as dizziness and electrocardiogram PR prolongation; fall, pleurothotonus and myoclonus were AEs that were not listed on the drug label. Moreover, we obtained 88 reports of AEs in men and 100 reports of AEs in women; somnolence was a common AE in both men and women and was more common in women, whereas pleurothotonus was a more common AE in men. In addition, we analyzed 12 AEs in patients younger than 18 years, 16 in patients between 18 and 65 years, and 113 in patients older than 65 years. The three age groups had distinctive AEs, but lethargy was the common AE among all age groups. Finally, the median time to AE onset was 19 days in all cases. In both men and women, most AEs occurred within a month of starting donepezil plus memantine, but some continued after a year of treatment.

Conclusion

Our study identified potential and new AEs of donepezil in combination with memantine; some of these AEs were the same as in the specification, and some of the AE signals were not shown in the specification. In addition, there were sex and age differences in some of the AEs. Therefore, our findings may provide valuable insights for further studies on the safety of donepezil and memantine combination therapy, which are expected to contribute to the safe use of this therapy in clinical practice.

Enhanced anti-amnestic effect of donepezil by Ginkgo biloba extract (EGb 761) via further improvement in pro-cholinergic and antioxidative activities

ETHNOPHARMACOLOGICAL RELEVANCE

EGb 761 is a standardized dry extract of Ginkgo biloba L. leaves traditionally used by Eastern Asia and has been associated with beneficial effects on neurodegeneration disorders, including Alzheimer's disease.

AIM OF THE STUDY

Since beneficial interactions between EGb 761 and donepezil have been observed in previous clinical studies, the current study was proposed aiming to further explore related mechanisms from both pharmacokinetics and pharmacodynamics aspects.

MATERIALS AND METHODS

Pharmacodynamic interactions were studied in scopolamine-induced cognitive impairment rats received two-weeks treatment of vehicle, EGb 761 and/or donepezil by the Morris water maze test and ex vivo evaluation of biomarkers of cholinergic transmission and oxidative stress in rat brain. In the meantime, pharmacokinetic profiles of donepezil and bilobalide were obtained and compared among all treatment groups. In addition, impact of the bioavailable EGb 761 components on donepezil brain penetration was evaluated with the hCMEC/D3 cell monolayer model.

RESULTS

Scopolamine-induced rats with co-treatment of EGb 761 and donepezil had significantly improved cognitive function in the Morris water maze test with increased brain levels of superoxide dismutase and decreased brain levels of acetylcholinesterase and malondialdehyde than that with treatment of only EGb 761 or donepezil. Despite such beneficial pharmacodynamics outcomes, the two-week co-treatment of EGb 761 and donepezil did not alter the plasma pharmacokinetics and brain uptake of donepezil or bilobalide, which was further verified in the hCMEC/D3 monolayer model.

CONCLUSION

Co-administration of EGb 761 and donepezil exerted better anti-amnestic effect via further enhanced pro-cholinergic and antioxidative effects of EGb 761 or donepezil in scopolamine-induced cognitive impairment rat without alteration in their systemic/brain exposure.

Potential Antimigraine Effects of Warfarin: An Exploration of Biological Mechanism with Survey of Patients

Case reports suggest a link between anticoagulant use and improved migraine symptoms, and a role for platelet-induced cerebral vasoconstriction in migraine pathobiology. Hence, we investigated the mechanism by which warfarin may affect migraine symptoms and whether there is a change in migraine symptomology in patients initiating oral anticoagulants, most commonly warfarin. The effects of warfarin on human platelet aggregation and secretion as well as platelet-induced rat cerebral artery vasoconstriction were studied. A survey of migraine and symptom change after starting or stopping oral anticoagulants was also conducted. Warfarin inhibited platelet aggregation and 5-hydroxytryptamine (5-HT) secretion in a concentration-dependent manner. Warfarin-inhibited platelet secretion products constricted middle cerebral arteries from male but not from female rats. For the survey, patient demographic information, migraine and medical history, and Migraine Disability Assessment Score (MIDAS) changes were collected. Out of 175 consenting, 40 respondents met the criteria for migraine and completed the survey. A total of 11 patients reported migraine symptom change, all coinciding with starting warfarin. Of those having symptom and MIDAS improvement, most were female with migraines with aura, whereas those worsening were male with fewer having migraine with aura. Of those reporting migraine symptom change with warfarin, female sex may be associated with improved MIDAS, and those experiencing an aura component are more likely to report a symptom change. Warfarin-mediated symptom improvement in females may occur due to inhibition of platelet 5-HT secretion and a lower sensitivity of female cerebral blood vessels to platelet-derived 5-HT-induced vasoconstriction.

Classics in Chemical Neuroscience: Donepezil

The discovery of acetylcholine and acetylcholinesterase provided the first insight into the intricacies of chemical signal transduction and neuronal communication. Further elucidation of the underlying mechanisms led to an attendant leveraging of this knowledge via the synthesis of new therapeutics designed to control aberrant biochemical processes. The central role of the cholinergic system within human memory and learning, as well as its implication in Alzheimer's disease, has made it a point of focus within the neuropharmacology and medicinal chemistry communities. This review is focused on donepezil and covers the background, synthetic routes, structure-activity relationships, binding interactions with acetylcholinesterase, pharmacokinetics and metabolism, efficacy, adverse effects, and historical importance of this leading therapeutic in the treatment of Alzheimer's disease and true Classic in Chemical Neuroscience.

The multi-functional drug tropisetron binds APP and normalizes cognition in a murine Alzheimer's model

Tropisetron was identified in a screen for candidates that increase the ratio of the trophic, neurite-extending peptide sAPPα to the anti-trophic, neurite-retractive peptide Aβ, thus reversing this imbalance in Alzheimer's disease (AD). We describe here a hierarchical screening approach to identify such drug candidates, moving from cell lines to primary mouse hippocampal neuronal cultures to in vivo studies. By screening a clinical compound library in the primary assay using CHO-7W cells stably transfected with human APPwt, we identified tropisetron as a candidate that consistently increased sAPPα. Secondary assay testing in neuronal cultures from J20 (PDAPP, huAPP(Swe/Ind)) mice showed that tropisetron consistently increased the sAPPα/Aβ 1-42 ratio. In in vivo studies in J20 mice, tropisetron improved the sAPPα/Aβ ratio along with spatial and working memory in mice, and was effective both during the symptomatic, pre-plaque phase (5-6 months) and in the late plaque phase (14 months). This ameliorative effect occurred at a dose of 0.5mg/kg/d (mkd), translating to a human-equivalent dose of 5mg/day, the current dose for treatment of postoperative nausea and vomiting (PONV). Although tropisetron is a 5-HT3 receptor antagonist and an α7nAChR partial agonist, we found that it also binds to the ectodomain of APP. Direct comparison of tropisetron to the current AD therapeutics memantine (Namenda) and donepezil (Aricept), using similar doses for each, revealed that tropisetron induced greater improvements in memory and the sAPPα/Aβ1-42 ratio. The improvements observed with tropisetron in the J20 AD mouse model, and its known safety profile, suggest that it may be suitable for transition to human trials as a candidate therapeutic for mild cognitive impairment (MCI) and AD, and therefore it has been approved for testing in clinical trials beginning in 2014.

Somatic comorbidities and Alzheimer's disease treatment

Therapeutic strategies in Alzheimer’s disease (AD) must take into account the characteristics of elderly people, who often have somatic comorbidities. Moreover, demented patients are more frequently frailer than older people. They have a higher number of admissions to hospital, a greater prevalence of complications and an increased risk of death. Therapeutic decisions for these patients have to be approached cautiously: aging, a more elevated comorbidity/polytherapy index and frailty contribute to enhance the risk of pharmacological adverse events and drug interactions. The aim of the present study was to focus on risk–benefit profile of pharmacological therapy for AD in relation to somatic comorbidities that often affect these patients. A Medline search (from 2001 to 2012) was performed using as key words dementia, Alzheimer’s disease, drug treatment, somatic comorbidities, side effects/adverse events and elderly. Cholinesterase inhibitors (ChEIs) and memantine represent the main pharmacological strategies effective in reducing the progression of cognitive decline and functional loss in AD. Many conditions very common in the elderly may restrict the use of ChEIs and/or treatment efficacy in AD patients. Memantine has a good efficacy and tolerability profile with better safety in pulmonary, cardiovascular and central nervous system comorbidities compared to ChEIs. Drug interactions with memantine are also more favorable since they concern mostly drugs not commonly used in the elderly. Only a careful evaluation of the associated somatic diseases, taking into account different drugs safety indexes and tolerability, can lead to personalized treatment management, in order to maximize drug efficacy and optimize quality of life.

Anticoagulation and psychotropic medications

Anticoagulants and psychotropic medications are commonly prescribed together. Thus, the potential for interaction exists. Whereas thrombolytics and heparins are implicated in few pharmacokinetic interactions, warfarin and platelet inhibitors have been implicated in various interactions with psychotropic medications. In this article, I review the various psychotropic drug classes' relationships to anticoagulants. In a field devoid of randomized, placebo-controlled trials, clinical vigilance is advised when managing patients on concomitant therapy.

Donepezil in the treatment of patients with Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and is characterized by an insidious onset and slow deterioration in cognition, activities of daily living (ADL), mood stability and social functioning. The cholinesterase inhibitors (ChEIs), developed based on the cholinergic hypothesis, are currently considered to be the best established treatment for AD, although the significant advances in the symptomatic pharmacotherapy of AD may be followed by disease-modification treatments. Donepezil is a mixed competitive and noncompetitive acetylcholinesterase inhibitor that shows a relative selectivity for acetylcholinesterase inhibitor compared with butyrylcholinesterase. In many clinical trials of donepezil, beneficial effects on standard measures of cognitive function, ADL and behavior have been shown in patients with mild, moderate or severe AD. Although the pharmacological and phamacokinetic profiles of the currently available ChEIs have notable differences that may affect efficacy, the clinical significance of these differences remains hypothetical in the absence of large, randomized trials that compare the ChEIs with each other.

Donepezil in Alzheimer's disease: From conventional trials to pharmacogenetics

Donepezil is the leading compound for the treatment of Alzheimer's disease (AD) in more than 50 countries. As compared with other conventional acetylcholinesterase inhibitors (AChEIs), donepezil is a highly selective and reversible piperidine derivative with AChEI activity that exhibits the best pharmacological profile in terms of cognitive improvement, responders rate (40%-58%), dropout cases (5%-13%), and side-effects (6%-13%) in AD. Although donepezil represents a non cost-effective treatment, most studies convey that this drug can provide a modest benefit on cognition, behavior, and activities of the daily living in both moderate and severe AD, contributing to slow down disease progression and, to a lesser exetnt, to delay institutionalization. Patients with vascular dementia might also benefit from donepezil in a similar fashion to AD patients. Some potential effects of donepezil on the AD brain, leading to reduced cortico-hippocampal atrophy, include the following: AChE inhibition, enhancement of cholinergic neurotransmission and putative modulation of other neurotransmitter systems, protection against glutamate-induced excitotoxicity, activation of neurotrophic mechanisms, promotion of non-amyloidodgenic pathways for APP processing, and indirect effects on cerebrovascular function improving brain perfusion. Recent studies demonstrate that the therapeutic response in AD is genotype-specific. Donepezil is metabolized via CYP-related enzymes, especially CYP2D6, CYP3A4, and CYP1A2. Approximately, 15%-20% of the AD population may exhibit an abnormal metabolism of AChEIs; about 50% of this population cluster would show an ultrarapid metabolism, requiring higher doses of AChEIs to reach a therapeutic threshold, whereas the other 50% of the cluster would exhibit a poor metabolism, displaying potential adverse events at low doses. In AD patients treated with a multifactorial therapy, including donepezil, the best responders are the CYP2D6-related extensive (EM)(*1/*1, *1/*10) (57.47%) and intermediate metabolizers (IM)(*1/*3, *1/*5, *1/*6, *7/*10) (25.29%), and the worst responders are the poor (PM) (*4/*4)(9.20%) and ultra-rapid metabolizers (UM) (*1xN/*1) (8.04%). Pharmacogenetic and pharmacogenomic factors may account for 75%-85% of the therapeutic response in AD patients treated with donepezil and other AChEIs metabolized via enzymes of the CYP family. The implementation of pharmacogenetic protocols can optimize AD therapeutics.

Donepezil in the treatment of dementia

Donepezil is an acetylcholinesterase inhibitor used to treat Alzheimer's disease. It has been shown to be effective in the treatment of cognitive symptoms, functional impairment and behavioral problems at mild, moderate and severe stages of the disease. Donepezil treatment results in modest short-term (6- to 9-month) improvement in some measures and attenuates the downward course of the disease for 1–3 years. Donepezil reaches peak plasma levels 3–4 h after ingestion and, with daily dosing, steady-state concentration in 14–21 days. The elimination half-life is approximately 70 h, and it is principally excreted unchanged in the urine. There is a linear relationship between plasma level and both red blood cell acetylcholinesterase inhibition and certain cognitive outcome measures. Donepezil is generally safe and well tolerated and, because of its dosing schedule, convenient to prescribe. Ongoing studies are examining the use of donepezil in combination with other drugs for Alzheimer's disease and for other conditions involving cognitive dysfunction.

Repeated dosing with donepezil does not affect the safety, tolerability or pharmacokinetics of single-dose thioridazine in young volunteers

AIM

To investigate the effects of donepezil at steady state on the safety, tolerability and pharmacokinetics of a single dose of thioridazine, in healthy subjects.

METHODS

An open, two-way, balanced crossover study, in 12 subjects (six men and six women) aged 19-41 years. During both treatment periods, subjects received a single oral dose of 50 mg thioridazine; in one period the thioridazine was given alone, and in the other period it was given together with the last of 15 daily, oral doses of donepezil 5 mg. The 'washout' periods were 1 week when thioridazine was given first, and 2 weeks when thioridazine was given last. Plasma concentrations of thioridazine were measured after each dose, and pharmacokinetic parameters were determined. Interactions were tested by using an equivalence analysis in which thioridazine was the 'Reference' and thioridazine + donepezil the 'Test' regimen. Safety and tolerability were monitored.

RESULTS

Donepezil had no marked effect on the pharmacokinetics of thioridazine, as judged by the equivalence analysis of AUC(0-tn), AUC(0-infinity), t((1/2)) and t(max). C(max) was very similar in the 'Test' and 'Reference' regimens, but the confidence intervals were too wide to confirm equivalence. Donepezil was well tolerated, whereas thioridazine was associated with light-headedness, tiredness and postural hypotension, irrespective of whether or not donepezil was given concurrently.

CONCLUSIONS

Repeated dosing with donepezil, 5 mg daily for 2 weeks, had no significant effect on the safety, tolerability or pharmacokinetics of thioridazine. Thioridazine was poorly tolerated.

Concurrent administration of donepezil HCl and risperidone in patients with schizophrenia: assessment of pharmacokinetic changes and safety following multiple oral doses

AIM

This open-label, multiple-dose trial investigated the effect of concurrent administration of donepezil HCl with risperidone on the pharmacokinetics (PK) and safety profiles of both drugs.

METHODS

Sixteen male patients with schizophrenia, who were receiving stable, physician-optimized risperidone (1-4 mg twice daily), and 15 healthy age- and weight-matched male controls, received donepezil HCl 5 mg daily for 7 days. Patients with schizophrenia remained on their physician-optimized dose of risperidone throughout the study. Pharmacokinetic parameters (C(max), t(max) and AUC) were assessed from plasma drug concentrations measured in blood collected before, during and after administration (for 12 h after risperidone on days 0 and 7, and for 24 h after donepezil HCl on day 7).

RESULTS

The mean age of all the subjects was 38.5 years. Donepezil PK parameters were similar between patients taking donepezil HCl + risperidone (AUC(0-24 h) = 329.0 +/- 17.2 ng x h ml(-1)) and controls taking donepezil HCl alone (AUC(0-24 h) = 354.7 +/- 28.2 ng x h ml(-1)). Pharmacokinetic parameters for risperidone and 9-OH risperidone were not altered in patients with schizophrenia after 7 days of donepezil HCl administration (AUC(0-12 h) standardized by dose: risperidone = 59.6 +/- 16.3 ng.h ml(-1) at day 0, 56.0 +/- 15.8 ng x h ml(-1) at day 7; 9-OH risperidone = 162.1 +/- 19.2 ng x h ml(-1) at day 0, 163.3 +/- 15.0 ng x h ml(-1) at day 7). The most common adverse event in both treatment groups was diarrhoea (6/16 risperidone + donepezil HCl patients and 9/16 donepezil HCl only subjects). There were no significant changes in physical examination, ECG, vital signs or treatment-emergent abnormal laboratory values associated with either of the treatment regimens. No subject developed extrapyramidal side-effects following donepezil administration.

CONCLUSIONS

These results suggest that once-daily dosing of 5 mg donepezil HCl does not alter the PK of risperidone in patients with schizophrenia. The combination of risperidone and donepezil HCl was well tolerated.

Concurrent administration of donepezil HCl and sertraline HCl in healthy volunteers: assessment of pharmacokinetic changes and safety following single and multiple oral doses

AIM

This study evaluated the safety and pharmacokinetics (PK) of donepezil HCl and sertraline HCl when administered separately and in combination.

METHODS

This was a randomized, open-label, three-period crossover study. In consecutive dosing periods separated by washout periods of > or = 3 weeks, healthy volunteers received either oral donepezil HCI 5 mg once daily for 15 days, oral sertraline HCl 50 mg once daily for 5 days followed by 10 days of once-daily sertraline HCl 100 mg, or the simultaneous administration of oral donepezil HCl and sertraline HCl. Plasma donepezil and sertraline concentrations were determined by high performance liquid chromatography/mass spectrometry. Safety was evaluated by physical and laboratory evaluations and the monitoring of adverse events (AEs).

RESULTS

A total of 19 volunteers (16 male and three female) were enrolled. Three male subjects withdrew from the study prematurely due to AEs (one case of nausea/stomach cramps and one case of eosinophilia during combination treatment, and one upper respiratory tract infection during treatment with sertraline HCl alone). In subjects who completed all three treatment periods (n = 16), the concurrent administration of donepezil HCl and sertraline HCl did not alter the steady-state (day 15) PK parameters of donepezil HCl. A small (< 12%) but statistically significant (P = 0.02) increase in donepezil C(max) was seen after single doses of sertraline HCl and donepezil HCl on day 1 but this was not thought to be clinically meaningful. No significant differences in the t(max) or AUC(0-24 h) of donepezil were observed between the donepezil HCl only or donepezil HCl plus sertraline HCl groups on day 1. No significant changes in sertraline PK parameters were observed either on day 1 (single dose) or on day 15 (steady state) when sertraline HCl was co-administered with donepezil HCl. Generally, the concurrent administration of donepezil HCl and sertraline HCl was well tolerated, with no serious AEs reported during the study. Some digestive system AEs tended to occur more frequently during combination treatment than with either treatment alone, but there was no statistically significant increase in the incidence of any individual AE. The most common AEs during the combination therapy were nausea and diarrhoea, which were rated as mild or moderate in severity. These AEs were also reported during the administration of each drug alone.

CONCLUSIONS

The co-administration of once-daily oral donepezil HCl 5 mg for 15 days and once-daily oral sertraline HCl (50 mg for 5 days increased to 100 mg for 10 days) did not result in any clinically meaningful pharmacokinetic interactions, and no unexpected AEs were observed.

The safety and tolerability of donepezil in patients with Alzheimer's disease

Cholinesterase (ChE) inhibitors, which prevent the hydrolysis of acetylcholine, have been approved for the symptomatic treatment of Alzheimer's disease (AD) for over a decade. However, the first ChE inhibitors were associated with a high incidence of side-effects and general tolerability concerns, including hepatotoxicity. Side-effects associated with increased cholinergic activity, particularly in the gastrointestinal (GI) system, can prevent patients from achieving effective doses of drug. In addition, the advanced age and frail nature of patients with AD mean that poor tolerability is a serious concern. The potential for drug-drug interactions is also an important consideration, due to the high prevalence of comorbid disease in these patients. Data both from clinical trials and studies in routine clinical practice have shown that donepezil is associated with a low incidence of GI adverse events (AEs) that is comparable with placebo. Donepezil is a potent, selective inhibitor of acetylcholinesterase, and selective inhibition of central as opposed to peripheral ChEs might be expected to reduce the incidence of AEs, thus this may explain the lower incidence of cholinergic AEs observed following treatment with donepezil, compared with nonselective ChE inhibitors. There are no differences in cardiovascular AEs, including bradycardia, between placebo and donepezil groups in the clinical trials published to date, even in a very sick vascular dementia population with high rates of comorbidity and concomitant medication use. Data from single- and multiple-dose studies of donepezil in patients with hepatic impairment and with moderately to severely impaired renal function indicate that donepezil is safe and well tolerated in these groups. Furthermore, both in vitro and clinical studies have shown that donepezil is not associated with drug-drug interactions. The incidence of weight loss is very similar between donepezil- and placebo-treated patients. Although insomnia and other sleep disorders have been reported following administration of donepezil, lengthening the time period before increasing the dose of donepezil from 5 to 10 mg day(-1) or switching to morning dosing can reduce these events to the levels of placebo-treated patients. Over 770 million days of patient use and an extensive publication database demonstrate that donepezil has a good tolerability and safety profile.

Human variability for metabolic pathways with limited data (CYP2A6, CYP2C9, CYP2E1, ADH, esterases, glycine and sulphate conjugation)

Human variability in the kinetics of a number of phase I (CYP2A6, CYP2C9, CYP2E1, alcohol dehydrogenase and hydrolysis) and phase II enzymes (glycine and sulphate conjugation) was analysed using probe substrates metabolised extensively (>60%) by these routes. Published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and available data on subgroups of the population (effects of ethnicity, age and disease) were abstracted using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration time-curve (AUC)] and acute exposure (C(max)). Interindividual differences in kinetics for all these pathways were low in healthy adults ranging from 21 to 34%. Pathway-related uncertainty factors to cover the 95th, 97.5th and 99th centiles of healthy adults were derived for each metabolic route and were all below the 3.16 kinetic default uncertainty factor in healthy adults, with the possible exception of CYP2C9*3/*3 poor metabolisers (based on a very limited number of subjects). Previous analyses of other pathways have shown that neonates represent the most susceptible subgroup and this was true also for glycine conjugation for which an uncertainty factor of 29 would be required to cover 99% of this subgroup. Neonatal data were not available for any other pathway analysed.

Drug interactions with cholinesterase inhibitors

Cholinesterase inhibitors are used for the symptomatic treatment of patients with Alzheimer's disease. This population often has numerous comorbidities and receives treatment with multiple medications. The astute clinician should remain mindful of possible drug interactions, both pharmacokinetic and pharmacodynamic, that may occur with concomitant treatment. Although pharmacokinetic interactions have been reported, pharmacodynamic interactions play a far greater role in the significance of drug interactions, with anticholinergic medications being most concerning. Commonly prescribed medications, such as antihistamines and tricyclic antidepressants, often have anticholinergic properties that alone or in combination with one another can antagonise the effects of cholinesterase inhibitors. Other medication classes such as antipsychotics and cholinergic agents may also result in pharmacodynamic interactions. However, for the most part, cholinesterase inhibitors can be used safely in combination with other medications.

Pharmacokinetic and safety assessments of concurrent administration of risperidone and donepezil

Treatment of Alzheimer's disease sometimes uses combinations of drugs because dementia is frequently associated with behavioral symptoms. Risperidone and donepezil are both metabolized through cytochrome P450 2D6 and 3A4, raising the possibility of drug interactions with combination therapy. The objective of this study was to determine whether significant drug interactions occur with concomitant administration of donepezil and risperidone. In an open-label, three-way crossover study, 24 healthy men were randomly assigned to receive 0.5 mg of risperidone twice daily, 5 mg of donepezil once daily, or both drugs for 14 consecutive days, followed by a 21-day washout period. The treatment ratios of AUC and associated 90% confidence intervals (CIs) for risperidone active moiety, defined as risperidone plus 9-hydroxyrisperidone (ratio = 110.2%; 90% CI = 103.7-117.2), and for donepezil (ratio = 97.1%; 90% CI = 90.0-103.6) were within the 80% to 125% of bioequivalence range. The treatment ratios of Cmax and associated 90% CIs for risperidone active moiety (ratio = 114.6%; 90% CI = 107.0-122.8) and for donepezil (ratio = 96.1%; 90% CI = 90.0-102.6) were also within the bioequivalence range. Therefore, no significant pharmacokinetic differences occurred in either risperidone active moiety or donepezil when given alone or in combination. Adverse events (predominantly headache, nervousness, and somnolence) were minor and comparable for all treatment groups. The results indicate that no clinically meaningful drug interactions occurred between risperidone 1 mg daily and donepezil 5 mg daily at steady state, and therefore no dosage adjustment is required when both drugs are combined with the dosage regimen studied. Additional investigations are warranted to determine the potential for interactions in elderly patients with dementia who may eliminate risperidone and donepezil more slowly and thus be more vulnerable to clinical drug interactions than the young healthy subjects examined in this study.

Cognitive pharmacotherapy of Alzheimer's disease and other dementias

OBJECTIVE

The objective of this paper is to review the randomized controlled trials (RCTs) on the pharmacotherapy of Alzheimer's disease and other dementias and to provide evidence-based recommendations for treatment of the cognitive impairment associated with these disorders.

METHOD

A Medline search was conducted for RCTs, using the following key words: Alzheimer's disease, dementia, therapy, cholinesterase inhibitor, donepezil, rivastigmine, and galantamine. Studies were critically appraised, followed by a review of published major clinical practice guidelines. Recommendations for treatment were made based on best available evidence.

RESULTS

The pharmacotherapy of Alzheimer's disease should include the meticulous management of vascular risk factors (for example, hypertension, diabetes, cholesterol, and stroke prophylaxis) and consideration for supplementation with folate, vitamin B complex, and vitamin E. Patients should be offered at least 1 trial of a cholinesterase inhibitor, with the possibility of another trial if the first is poorly tolerated or ineffective. Patients with vascular dementia and dementia with Lewy bodies should also be offered treatment with cholinesterase inhibitors. At this time, we lack sufficient data to recommend the use of hormone replacement or antiinflammatory therapy for treatment of dementia as the primary indication.

CONCLUSION

Reasonable evidence exists to provide recommendations for the pharmacotherapy of dementia. Treatment will likely result in modest but important benefits to patients, caregivers, and society.

Effect of modafinil at steady state on the single-dose pharmacokinetic profile of warfarin in healthy volunteers

Modafinil has been reported to produce a concentration-related suppression of CYP2C9 activity in vitro in primary cultures of human hepatocytes. To determine whether this effect occurs in vivo, the pharmacokinetics of (S)-warfarin was investigated after single oral doses of racemic warfarin (5 mg; COUMADIN) in a placebo-controlled, single-blind, single-period study in 28 volunteers. Subjects received an oral dose of warfarin prior to administration of modafinil (200 mg for 7 days, followed by 400 mg for 21 days) or placebo and they received another after 4 weeks of treatment. Treatment with modafinil did not significantly alter the pharmacokinetics of (S)- or (R)-warfarin relative to placebo. Since (S)-warfarin is predominantly metabolized via CYP2C9, the results indicate that the marked suppression of CYP2C9 activity in vitro does not translate into a similar effect clinically. However, limitations arising from investigation of single doses of warfarin preclude global conclusions about the potential for more subtle interactions after chronic warfarin administration.

Donepezil for Alzheimer's disease: pharmacodynamic, pharmacokinetic, and clinical profiles

Donepezil was developed in order to overcome the disadvantages of physostigmine and tacrine. Its use is based on the cholinergic hypothesis. Donepezil is a piperidine-based, reversible acetylcholinesterase inhibitor, that is chemically unrelated to other cholinesterase inhibitors. It was developed for the symptomatic treatment of Alzheimer's disease (AD). Donepezil is highly selective for acetylcholinesterase with a significantly lower affinity for butyrylcholinesterase, which is present predominantly in the periphery. Phase I and II clinical trials demonstrated donepezil's favorable pharmacokinetic, pharmacodynamic and safety profile. There is no need to modify the dose of donepezil in the elderly or in patients with renal and hepatic failure. Pivotal phase-III trials in the US, European countries, and Japan showed that donepezil significantly improved cognition and global function in patients with mild to moderate AD. In long-term trials, donepezil maintained cognitive and global function for up to 1 year prior to the resumption of gradual deterioration. Donepezil is generally well tolerated; most of its adverse events are mild, transient and cholinergic in nature. Donepezil produces no clinically significant changes in laboratory parameters, including liver function. The drug is approved for the treatment of mild to moderate Alzheimer's disease, but donepezil therapy does not have to be discontinued if a patient continues to deteriorate. Possible new indications for donepezil in psychiatric and neurologic diseases, other than AD, include dementia with Lewy bodies, brain injury, attention deficit hyperactivity, multiple sclerosis, Down's syndrome, delirium, mood disorders, Huntington's disease and sleep disorders.

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

Donepezil (E-2020) is a reversible, noncompetitive, piperidine-type cholinesterase inhibitor. It is selective for acetylcholinesterase rather than butyrylcholinesterase. Donepezil 5 and 10 mg/day significantly improved cognition and global clinical function compared with placebo in well designed short term trials (14 to 30 weeks) in 161 to 818 patients with mild to moderate Alzheimer's disease. Beneficial effects on cognition were observed from week 3 of treatment. Donepezil 10 mg/day significantly delayed the deterioration in activities of daily living (ADL) [by 55 weeks] compared with placebo in a retrospective analysis of 1 trial, and in the largest trial significantly improved patients' abilities to perform complex tasks. However, no significant improvement in function was observed with donepezil 5 mg/day in another trial. In the 2 trials of longest duration donepezil (5 and 10 mg) significantly delayed symptomatic progression of the disease. While there was no evidence for a positive effect of donepezil on patients' quality of life, there are no validated measures of this parameter specific to patients with Alzheimer's disease. Donepezil (5 and 10 mg) significantly reduced caregiver burden. Long term efficacy data suggest that improvements in cognition, global function or ADL are maintained for about 21 to 81 weeks with donepezil (10 mg/day in most patients). Donepezil is generally well tolerated with the majority of adverse events being mild and transient. Predictably, most events were cholinergic in nature and generally related to the gastrointestinal and nervous systems. The incidence of these events was significantly higher with donepezil 10 mg than with placebo in short term clinical trials; however, this may have been due to the 7-day dose increase schedule used in these studies and can be minimised by increasing the dose after a longer (6-week) period. The incidence of serious adverse events was generally similar between donepezil 5 and 10 mg (4 to 10%) and placebo (5 to 9%) in short term trials. 26% of patients receiving donepezil (5 and 10 mg) reported serious events over a 98-week period in a long term trial. Importantly, there was no evidence of hepatotoxicity with this drug. Conclusions. Donepezil (5 and 10 mg) is an agent with a simple once-daily dosage schedule which improves cognition and global clinical function in the short (up to 24 weeks) and long term (up to about 1 year) in patients with mild to moderate Alzheimer's disease. Improvements in ADL were also observed with donepezil 10 mg/day. Adverse events associated with donepezil are mainly cholinergic. Donepezil has been extensively studied and should be considered as a first-line treatment in patients with mild to moderate Alzheimer's disease.

An economic perspective on Alzheimer's disease

The rapid growth of the world's Alzheimer's disease (AD) population has resulted in a tremendous financial burden on society, a situation exacerbated by the fact that the funding of health and social services faces increasing restrictions in the coming years. As a consequence, several cost-of-illness studies, aimed at assessing the total costs associated with the care of an AD patient or with individual components thereof, have been conducted, with a view to identifying areas in which costs might be reduced. For example, the Costs of Dementia (CoDem) study, described here, aims to give a profile of the total economic costs of AD in Italy. While this study found the number of Instrumental Activities of Daily Living lost to be the principal predictor of the weekly costs for home care, other studies have reported a correlation between total cost and Mini-Mental State Examination (MMSE) score. The basis for a correlation between cost and disease severity is discussed. Pharmacoeconomics aims to assess the cost effectiveness of interventions that may form part of an overall management strategy in AD. As institutionalization is the largest cost element in the care of any AD patient, efforts at cost containment have focused on maintaining patients at home for as long as possible. The results of studies on a number of interventions, namely, screening, reality orientation therapy, special care units, family interventions, and drug treatment, are discussed, although the costs and, indeed, the long-term benefits associated with many of these remain unknown. Although information concerning costs is essential in health resource allocation, it is also vital that meaningful ways in which to assess quality-of-life issues be developed as the basis for genuine cost-benefit judgments.

Rational design of anti-dementia therapy

Understanding the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of new drugs is essential. The application of this information facilitates the design of a rational clinical trial programme and optimizes the chances for rapid and successful clinical development. Upon completion of each development phase, the information obtained must be evaluated critically to maximize the design of subsequent studies. Phase I trials represent the first time the drug is administered in humans and their primary objective is to evaluate the drug's safety and tolerability in man. Phase II trials represent the first time that the drug is administered to the target patient population. The objectives of Phase II trials are to verify the safety and tolerability of the drug in patients, and also to evaluate for the first time the clinical efficacy of the drug. During these phases of development, the use of PK and PD measures is helpful for establishing the therapeutic dose range as well as the suitability of the chosen efficacy measures for use in the pivotal Phase III trials. Here, using several examples of PK and PD data obtained from the clinical development studies of donepezil HCl, the application of these measures on the development of a drug for the treatment of Alzheimer's disease is discussed.