Cholinesterase inhibitors for patients with Alzheimer's disease: syste
http://www.100md.com
《英国医生杂志》
1 Department of Primary Medical Care, Center of Psychosocial Medicine, University Medical Center Hamburg-Eppendorf, Martinistra?e 52, D-20246 Hamburg, Germany
Corresponding author: H Kaduszkiewicz kaduszki@uke.uni-hamburg.de
Objectives Pharmacological treatment of Alzheimer's disease focuses on correcting the cholinergic deficiency in the central nervous system with cholinesterase inhibitors. Three cholinesterase inhibitors are currently recommended: donepezil, rivastigmine, and galantamine. This review assessed the scientific evidence for the recommendation of these agents.
Data sources The terms "donepezil", "rivastigmine", and "galantamine", limited by "randomized-controlled-trials" were searched in Medline (1989-November 2004), Embase (1989-November 2004), and the Cochrane Database of Systematic Reviews without restriction for language.
Study selection All published, double blind, randomised controlled trials examining efficacy on the basis of clinical outcomes, in which treatment with donepezil, rivastigmine, or galantamine was compared with placebo in patients with Alzheimer's disease, were included. Each study was assessed independently, following a predefined checklist of criteria of methodological quality.
Results 22 trials met the inclusion criteria. Follow-up ranged from six weeks to three years. 12 of 14 studies measuring the cognitive outcome by means of the 70 point Alzheimer's disease assessment scale—cognitive subscale showed differences ranging from 1.5 points to 3.9 points in favour of the respective cholinesterase inhibitors. Benefits were also reported from all 12 trials that used the clinician's interview based impression of change scale with input from caregivers. Methodological assessment of all studies found considerable flaws—for example, multiple testing without correction for multiplicity or exclusion of patients after randomisation.
Conclusion Because of flawed methods and small clinical benefits, the scientific basis for recommendations of cholinesterase inhibitors for the treatment of Alzheimer's disease is questionable.
Currently the three cholinesterase inhibitors donepezil, rivastigmine, and galantamine are widely recommended for clinical use. The National Institute for Clinical Excellence (NICE, now National Institute for Health and Clinical Excellence), for example, says in its guidance for treatment of Alzheimer's disease that the three drugs should be made available in the NHS as one component of the management of people with mild and moderate Alzheimer's disease.1 The American Academy of Neurology also recommends cholinesterase inhibitors, although the average benefit seems small.2 The rationale for these recommendations is that evidence from randomised controlled trials has shown that all three drugs have beneficial effects on cognitive and global outcome measures. However, cholinesterase inhibitors are not widely prescribed. In Germany, donepezil, rivastigmine, and galantamine account for 10% of all antidementia drugs prescribed in 2003.3 The gap between multiple recommendations of these agents and their lack of use in daily clinical practice prompted us to review all available randomised controlled trials. The objective of this review is to explore the scientific evidence for the clinical use of donepezil, rivastigmine, and galantamine.
Methods
We searched the termsn "donepezil", "rivastigmine", and "galantamine", limited by "randomized-controlled-trials" in Medline (1989-November 2004), Embase (1989-November 2004), and the Cochrane Database of Systematic Reviews, without restriction for language. Additionally we checked the bibliographical data of all included publications for further studies. We included all papers presenting original data of randomised, double blind, placebo controlled trials with donepezil, rivastigmine, or galantamine in patients with Alzheimer's disease and excluded trials that did not examine clinical outcomes or focused on vascular dementia. As the aim of our review was to explore the scientific evidence for the clinical benefits claimed for cholinesterase inhibitors and not to compare the benefits of the various cholinesterase inhibitors with each other, we did not include head to head comparisons in the analysis. Three of the authors (HK, TZ, HPBB) read each of the studies that met the inclusion criteria and assessed them independently, following a predefined checklist of criteria of methodological quality that was partly related to the CONSORT statement4 (table A on bmj.com). Some items of the checklist relate to findings, others to the study design, but we considered all to be important for a comprehensive interpretation of the results. We discussed every trial in detail, and at the end of the discussion process a joint assessment of each trial was achieved.
Results
Our literature search yielded a total of 412 references, of which 19 publications met the inclusion criteria. In addition we reviewed the bibliographies of the identified studies and of all available reviews for further studies, which yielded three additional papers. We identified 12 original publications of randomised controlled trials on donepezil,5-16 five on rivastigmine,17-21 and five on galantamine.22-26 Table B on bmj.com shows the main characteristics and results of these 22 randomised controlled trials.
The duration of treatment varied between six weeks9 and three years.15 The number of patients included per study varied between 2721 and 978.24 All studies included patients with an established diagnosis of probable or possible Alzheimer's disease, according to the National Institute of Neurological and Communicative Disorders and Stroke—Alzheimer Disease and Related Disorders Association,27 with one exception where a DSM-IV diagnosis of dementia was used for inclusion.15 In eight of the 22 trials, one primary efficacy measurement was used.9 12-14 16 17 21 26 The remaining 14 trials combined several instruments to assess efficacy of treatment or performed multiple analyses by using the same instrument.
Assessment tools used
Fourteen of 22 trials used the Alzheimer's disease assessment scale—cognitive subscale (ADAS-cog28) as the primary measurement of efficacy.5-10 18-20 22-26 This is a psychometric scale consisting of 11 items that evaluate selected aspects of memory, orientation, attention, language, reasoning, and carrying out instructions. Its score ranges from 0 (no impairment) to 70 (very severe impairment). In 12 of the 14 trials that used the scale, significant differences between cholinesterase inhibitor and placebo groups were reported, always favouring the treatment groups.5-10 18 22-26 The mean differences between treatment and placebo groups ranged from 1.5 points to 3.9 points.
In 12 trials, the clinician's interview based impression of change scale with caregiver input (CIBIC-plus29) was used to assess efficacy.6-8 11 18-25 This instrument uses information obtained during an independent clinical interview to assess disease severity and progression. A blinded clinician conducts interviews with patient and caregiver. The severity of the disease is rated at baseline and at subsequent visits. Change from baseline is scored by using a 7 point Likert-type scale, in which 1 represents marked improvement, 4 no change, and 7 marked worsening. Only full scores from 1 to 7 are used.
The differences on the CIBIC-plus scale between intervention and control groups were calculated in various manners in the trial reports. In five trials, differences of mean values between groups were calculated.6 7 11 18 20 In all five trials, significant benefits of the cholinesterase inhibitor were found; differences ranged from 0.26 points to 0.54 points. Eleven trials compared proportions of patients with a benefit on the CIBIC-plus scale in each of the groups.6-8 11 19-25 "Benefit" was defined as scores from 1-3, or 1-4—that is, the cut-off point for "benefit" was defined in different ways in the various trials. In all 11 trials, significant differences were reported in at least one of the treatment groups compared with placebo—again favouring treatment with cholinesterase inhibitors. However, in five trials7 19 22 24 25 statistical significance vanished in all dose groups after multiplicity has been corrected for, or after considering exclusion of patients in a worst case scenario.
In 10 trials, other instruments were used to evaluate the primary end point(s). In the trial reported by Mohs et al,12 the primary end point was time in days to reach clinically evident functional decline. Donepezil extended the median time to clinically evident functional decline by five months compared with placebo. The AD2000 Collaborative Group15 used as primary end points entry to institutional care and progression of disability. No significant differences were seen in either primary end point.
Tariot et al13 used the neuropsychiatric inventory30 31 as their endpoint measure. No difference between the donepezil and placebo group was found. Holmes et al16 also used the neuropsychiatric inventory as their endpoint measure. The results show a negative effect of withdrawal of donepezil. Winblad et al14 used the Gottfries-Brane-Steen scale32 and found no difference between donepezil and placebo. In three trials,5 10 17 efficacy of treatment was assessed by means of the clinical global impression of change (CGIC33) scale, which is similar to the CIBIC-plus scale. Agid et al17 reported a difference between the 6 mg rivastigmine and the control group, but significance was lost after correction for multiplicity. Rogers et al5 found no difference, whereas Homma et al10 found a significant difference favouring donepezil.
Corey-Bloom et al18 and R?sler et al20 used the progressive deterioration scale (PDS34) as their primary outcome measure. In both trials, significant differences favouring rivastigmine were reported. In the study by R?sler et al,20 significance was lost after correction for multiplicity.
Methodological quality of the trials
Assessment of methodological quality of the 22 randomised controlled trials brought to attention numerous shortcomings (tables 1 and 2).
Table 1 Methodological shortcomings of 12 randomised controlled trials on donepezil
Table 2 Methodological shortcomings of five randomised controlled trials on rivastigmine and five on galantamine
A common shortcoming is the use of several "primary end points without correction for multiple comparisons (see note in table 1). After correction, two of the five trials on rivastigmine do not show any significant benefit on primary endpoint measures any more.17 19
Missing intention to treat analysis
Another shortcoming is a missing intention to treat analysis, as in 15 of the 22 trials patients were excluded from analysis after randomisation (table 1, "Missing patients,"6 7 9-12 14 17 19 20 22-26). In four trials, the number of participants included in endpoint analyses in each group was not reported at all or only partially.5 8 13 15 Consequently, in these four trials the dimension of potential bias emerging through exclusion of patients cannot even be estimated. Depending on the results, exclusion of patients might become very important when mean differences are calculated between treatment groups, because exclusion of only a few patients with extreme results might change the average results considerably. Unfortunately no information is provided in the reports that would allow the reader to assess the impact of excluding patients after randomisation. Furthermore, the calculation of means might be misleading even if patients are not excluded—for example, if a small proportion of patients benefits largely from treatment, the mean value might indicate an improvement even if treatment is slightly harmful for most.
Incomplete data
The handling of incomplete data (dropouts) constitutes another important problem. In at least eight of the trials6-8 16 23 24 25-26 the last observation carried forward (LOCF) method was used to include dropouts into endpoint analyses. This means that the last evaluation before dropout is defined as the endpoint measure. Since Alzheimer's disease is a progressive illness, early discontinuation of treatment because of side effects will pretend a reduced progression of the disease in endpoint analyses using last observation carried forward. In five trials using this method,6 7 23 25 26 dropout rates tended to be considerably higher in the treatment groups, which must have biased the results substantially. But even if dropout rates are equal in treatment and placebo groups, knowledge of dropout time is important to estimate possible bias. However, the exact time of dropouts is reported in none of the trials.
Different design and methodological flaws
Three studies need to be discussed separately as their design or methodological flaws differ from most of the reviewed trials. Mohs et al12 used as their primary end point the "median time in days to reach clinically evident functional decline," defined as a decline of at least one point in "basic activities of daily living (ADL)" or "instrumental activities of daily living" according to the Alzheimer's disease functional assessment and change scale or an increase in global clinical dementia rating of 1 point or more (all measures compared with baseline). The authors report that investigators were instructed to use these criteria. However, the final decision to remove a patient from the assigned treatment was left to the clinical judgment of the investigator. This is a methodological shortcoming since investigators could employ subjective measures to withdraw patients from the trial. Furthermore, 26% of placebo patients and 28% of donepezil patients discontinued the trial prematurely without reaching the predefined end point, which affects the results considerably. A further shortcoming is the restriction to report clinically evident functional decline over a period of only 48 weeks, although the study lasted for 54 weeks.
The AD2000 Collaborative Group15 used as its primary end points entry to institutional care and, similarly to Mohs et al,12 progression of disability. One important methodological flaw is that the duration of the study was not defined in advance. In addition, the results are presented for the combined groups receiving 5 mg and 10 mg donepezil, although groups should have been tested separately. Therefore this study can neither be used as a proof of inefficacy nor as a proof of efficacy of donepezil.
Holmes et al16 report that patients with Alzheimer's disease and neuropsychiatric symptoms were treated with open label donepezil for 12 weeks. During this treatment phase, patients with poor compliance, adverse events, and deterioration of neuropsychiatric symptoms or cognitive capacity were excluded. The remaining patients were randomised (double blind) between continuation of treatment and withdrawal of drug. The results show a negative effect of withdrawal of donepezil: neuropsychiatric symptoms increased when the drug was withdrawn. However, side effects of drug withdrawal are no proof for the efficacy of donepezil.
Adverse events of cholinesterase inhibitors
As shown in tables 3 and 4, donepezil, rivastigmine, and galantamine caused a broad spectrum of adverse events—nausea, vomiting, diarrhoea, and weight loss were the most common. The tables show the proportions of adverse events observed in patients in whom the difference between the cholinesterase inhibitor and placebo reached significance at the 5% level.
Table 3 Patients with adverse events in the donepezil and placebo groups (actual data because testing for significance is not appropriate for rare effects owing to insufficient power)
Table 4 Patients with adverse events in the trials on rivastigmine and galantamine (actual data because testing for significance is not appropriate for rare effects because of insufficient power)
As adverse events are typical for cholinesterase inhibitors, they can affect the efficiency of blinding, because the raters might be able to guess the patient's treatment.
Discussion
National Institute for Clinical Excellence (NICE). Guidance on the use of donepezil, rivastigmine and galantamine for the treatment of Alzheimer's disease. London: NICE, 2001.
Doody RS, Stevens JC, Beck C, Dubinsky RM, Kaye JA, Gwyther L, et al. Practice parameter: management of dementia (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 2001;56: 1154-66.
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Rogers SL, Friedhoff LT. The efficacy and safety of donepezil in patients with Alzheimer's disease: results of a US multicentre, randomized, double-blind, placebo-controlled trial. Dementia 1996;7: 293-303.
Rogers SL, Doody RS, Mohs RC, Friedhoff LT, and the Donepezil Study Group. Donepezil improves cognition and global function in Alzheimer disease: a 15-week, double-blind, placebo-controlled study. Arch Intern Med 1998;158: 1021-31. (Rogers 1998a in table 3.)
Rogers SL, Farlow MR, Doody RS, Mohs R, Friedhoff LT, and the Donepezil Study Group. A 24-week, double-blind, placebo-controlled trial of donepezil in patients with Alzheimer's disease. Neurology 1998;50: 136-45. (Rogers 1998b in table 3.)
Burns A, Friedhoff LT, Gauthier S, Hecker J, Moller HJ, Petit H, et al. The effects of donepezil in Alzheimer's disease—results from a multinational trial. Dement Geriatr Cogn Disord 1999;10: 237-44.
Greenberg SM, Tennis MK, Brown LB, Gomez-Isla T, Hayden DL, Schoenfeld DA, et al. Donepezil therapy in clinical practice: a randomised crossover study. Arch Neurol 2000;57: 94-9.
Homma A, Takeda M, Imai Y, Udaka F, Hasegawa K, Kameyama M, et al. Clinical efficacy and safety of donepezil on cognitive and global function in patients with Alzheimer's disease: a 24-week, multicenter, double-blind, placebo-controlled study in Japan. Dement Geriatr Cogn Disord 2000;11: 299-313.
Feldman H, Gauthier S, Hecker J, Vellas B, Subbiah P, Whalen E, and the Donepezil MSAD Study Investigators Group. A 24-week, randomized, double-blind study of donepezil in moderate to severe Alzheimer's disease. Neurology 2001;57: 613-20.
Mohs RC, Doody RS, Morris JC, Ieni JR, Rogers SL, Perdomo CA, et al. A 1-year, placebo-controlled preservation of function survival study of donepezil in AD patients. Neurology 2001;57: 481-8.
Tariot PN, Cummings JL, Katz IR, Mintzer, J, Perdomo CA, Schwam EM, Whalen E, and the Donepezil Nursing Home Study Investigators Group. A randomized, double-blind, placebo-controlled study of the efficacy and safety of donepezil in patients with Alzheimer's disease in the nursing home setting. J Am Geriatr Soc 2001;49: 1590-9.
Winblad B, Engedal K, Soininen H, Verhey F, Waldemar G, Wimo A, et al. A 1-year, randomized, placebo-controlled study of donepezil in patients with mild to moderate AD. Neurology 2001;57: 489-95.
AD2000 Collaborative Group. Long-term donepezil treatment in 565 patients with Alzheimer's disease (AD2000): randomised double-blind trial. Lancet 2004;363: 2105-15.
Holmes C, Wilkinson D, Dean C, Vethanayagam S, Olivieri S, Langley A, et al. The efficacy of donepezil in the treatment of neuropsychiatric symptoms in Alzheimer disease. Neurology 2004;63: 214-9.
Agid Y, Dubois B, on behalf of the International Rivastigmine Investigators, Anand R, Gharabawi G. Efficacy and tolerability of rivastigmine in patients with dementia of the Alzheimer type. Curr Ther Res Clin Exp 1998;59: 837-45.
Corey-Bloom J, Anand R, Veach J, for the ENA 713 B352 Study Group. A randomized trial evaluating the efficacy and the safety of ENA 713 (rivastigmine tartrate), a new acetylcholinesterase inhibitor, in patients with mild to moderately severe Alzheimer's disease. Int J Geriatr Psychopharmacol 1998;1: 55-65.
Forette F, Anand R, Gharabawi G. A phase II study in patients with Alzheimer's disease to assess the preliminary efficacy and maximum tolerated dose of rivastigmine (Exelon). Eur J Neurol 1999;6: 423-9.
Rosler M, Anand R, Cicin-Sain A, Gauthier S, Agid Y, Dal-Bianco P, et al. Efficacy and safety of rivastigmine in patients with Alzheimer's disease: international randomised controlled trial. BMJ 1999;318: 633-40.
Potkin SG, Anand R, Fleming, K, et al. Brain metabolic and clinical effects of rivastigmine in Alzheimer's disease. Int J Neuropsychopharmacol 2001;4: 223-30.
Raskind MA, Peskind ER, Wessel T, Yuan W, and the Galantamine USA-1 Study Group. A 6-month randomized, placebo-controlled trial with a 6-month extension. Neurology 2000;54: 2261-8.
Rockwood K, Mintzer J, Truyen L, Wessel T, Wilkinson D. Effects of a flexible galantamine dose in Alzheimer's disease: a randomized, controlled trial. J Neurol Neurosurg Psychiatry 2001;71: 589-95.
Tariot PN, Solomon PR, Morris JC, Kershaw P, Lilienfeld S, Ding C. A 5-month, randomized, placebo-controlled trial of galantamine in AD. Neurology 2000;54: 2269-76.
Wilcock GK, Lilienfeld S, Gaens E on behalf of the Galantamine International-1 Study Group. Efficacy and safety of galantamine in patients with mild to moderate Alzheimer's disease: multicentre randomised controlled trial. BMJ 2000;321: 1-7.
Wilkinson D, Murray J, in collaboration with the Galantamine Research Group. Galantamine: a randomized, double-blind, dose comparison in patients with Alzheimer's disease. Int J Geriatr Psychiatry 2001;16: 852-7.
McKhann G, Drachman D, Folstein M, Katzman R, Price D, Stadlan EM. Clinical Diagnosis of Alzheimer's Disease: report of the NINCDS/ADRDA work group under the auspices of the Department of Health and Human Services Task Force on Alzheimer's Disease. Neurology 1984;34: 939-44.
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Reisberg B, Ferris SH. CIBIC-Plus Interview Guide. East Hanover, NJ: Sandoz Pharmaceuticals Corporation, 1994.
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Guy W, ed. Clinical global impressions (CGI). In: ECDEU assessment manual for psychopharmacology. Rockville, MD: National Institutes for Mental Health 1976; 207-12.
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Florack C, Franz H, Kaiser T, Sawicki PT. The value of donepezil in the drug therapy of Alzheimer's disease . Offizielles Mitteilungsblatt der KV Sachsen-Anhalt 2002; 1-3.
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Ritchie CW, Ames D, Clayton T, Lai R. Metaanalysis of randomized trials of the efficacy and safety of donepezil, galantamine, and rivastigmine for the treatment of Alzheimer disease. Am J Geriatr Psychiatry 2004;12: 358-69.(Hanna Kaduszkiewicz, research fellow1, T)
Corresponding author: H Kaduszkiewicz kaduszki@uke.uni-hamburg.de
Objectives Pharmacological treatment of Alzheimer's disease focuses on correcting the cholinergic deficiency in the central nervous system with cholinesterase inhibitors. Three cholinesterase inhibitors are currently recommended: donepezil, rivastigmine, and galantamine. This review assessed the scientific evidence for the recommendation of these agents.
Data sources The terms "donepezil", "rivastigmine", and "galantamine", limited by "randomized-controlled-trials" were searched in Medline (1989-November 2004), Embase (1989-November 2004), and the Cochrane Database of Systematic Reviews without restriction for language.
Study selection All published, double blind, randomised controlled trials examining efficacy on the basis of clinical outcomes, in which treatment with donepezil, rivastigmine, or galantamine was compared with placebo in patients with Alzheimer's disease, were included. Each study was assessed independently, following a predefined checklist of criteria of methodological quality.
Results 22 trials met the inclusion criteria. Follow-up ranged from six weeks to three years. 12 of 14 studies measuring the cognitive outcome by means of the 70 point Alzheimer's disease assessment scale—cognitive subscale showed differences ranging from 1.5 points to 3.9 points in favour of the respective cholinesterase inhibitors. Benefits were also reported from all 12 trials that used the clinician's interview based impression of change scale with input from caregivers. Methodological assessment of all studies found considerable flaws—for example, multiple testing without correction for multiplicity or exclusion of patients after randomisation.
Conclusion Because of flawed methods and small clinical benefits, the scientific basis for recommendations of cholinesterase inhibitors for the treatment of Alzheimer's disease is questionable.
Currently the three cholinesterase inhibitors donepezil, rivastigmine, and galantamine are widely recommended for clinical use. The National Institute for Clinical Excellence (NICE, now National Institute for Health and Clinical Excellence), for example, says in its guidance for treatment of Alzheimer's disease that the three drugs should be made available in the NHS as one component of the management of people with mild and moderate Alzheimer's disease.1 The American Academy of Neurology also recommends cholinesterase inhibitors, although the average benefit seems small.2 The rationale for these recommendations is that evidence from randomised controlled trials has shown that all three drugs have beneficial effects on cognitive and global outcome measures. However, cholinesterase inhibitors are not widely prescribed. In Germany, donepezil, rivastigmine, and galantamine account for 10% of all antidementia drugs prescribed in 2003.3 The gap between multiple recommendations of these agents and their lack of use in daily clinical practice prompted us to review all available randomised controlled trials. The objective of this review is to explore the scientific evidence for the clinical use of donepezil, rivastigmine, and galantamine.
Methods
We searched the termsn "donepezil", "rivastigmine", and "galantamine", limited by "randomized-controlled-trials" in Medline (1989-November 2004), Embase (1989-November 2004), and the Cochrane Database of Systematic Reviews, without restriction for language. Additionally we checked the bibliographical data of all included publications for further studies. We included all papers presenting original data of randomised, double blind, placebo controlled trials with donepezil, rivastigmine, or galantamine in patients with Alzheimer's disease and excluded trials that did not examine clinical outcomes or focused on vascular dementia. As the aim of our review was to explore the scientific evidence for the clinical benefits claimed for cholinesterase inhibitors and not to compare the benefits of the various cholinesterase inhibitors with each other, we did not include head to head comparisons in the analysis. Three of the authors (HK, TZ, HPBB) read each of the studies that met the inclusion criteria and assessed them independently, following a predefined checklist of criteria of methodological quality that was partly related to the CONSORT statement4 (table A on bmj.com). Some items of the checklist relate to findings, others to the study design, but we considered all to be important for a comprehensive interpretation of the results. We discussed every trial in detail, and at the end of the discussion process a joint assessment of each trial was achieved.
Results
Our literature search yielded a total of 412 references, of which 19 publications met the inclusion criteria. In addition we reviewed the bibliographies of the identified studies and of all available reviews for further studies, which yielded three additional papers. We identified 12 original publications of randomised controlled trials on donepezil,5-16 five on rivastigmine,17-21 and five on galantamine.22-26 Table B on bmj.com shows the main characteristics and results of these 22 randomised controlled trials.
The duration of treatment varied between six weeks9 and three years.15 The number of patients included per study varied between 2721 and 978.24 All studies included patients with an established diagnosis of probable or possible Alzheimer's disease, according to the National Institute of Neurological and Communicative Disorders and Stroke—Alzheimer Disease and Related Disorders Association,27 with one exception where a DSM-IV diagnosis of dementia was used for inclusion.15 In eight of the 22 trials, one primary efficacy measurement was used.9 12-14 16 17 21 26 The remaining 14 trials combined several instruments to assess efficacy of treatment or performed multiple analyses by using the same instrument.
Assessment tools used
Fourteen of 22 trials used the Alzheimer's disease assessment scale—cognitive subscale (ADAS-cog28) as the primary measurement of efficacy.5-10 18-20 22-26 This is a psychometric scale consisting of 11 items that evaluate selected aspects of memory, orientation, attention, language, reasoning, and carrying out instructions. Its score ranges from 0 (no impairment) to 70 (very severe impairment). In 12 of the 14 trials that used the scale, significant differences between cholinesterase inhibitor and placebo groups were reported, always favouring the treatment groups.5-10 18 22-26 The mean differences between treatment and placebo groups ranged from 1.5 points to 3.9 points.
In 12 trials, the clinician's interview based impression of change scale with caregiver input (CIBIC-plus29) was used to assess efficacy.6-8 11 18-25 This instrument uses information obtained during an independent clinical interview to assess disease severity and progression. A blinded clinician conducts interviews with patient and caregiver. The severity of the disease is rated at baseline and at subsequent visits. Change from baseline is scored by using a 7 point Likert-type scale, in which 1 represents marked improvement, 4 no change, and 7 marked worsening. Only full scores from 1 to 7 are used.
The differences on the CIBIC-plus scale between intervention and control groups were calculated in various manners in the trial reports. In five trials, differences of mean values between groups were calculated.6 7 11 18 20 In all five trials, significant benefits of the cholinesterase inhibitor were found; differences ranged from 0.26 points to 0.54 points. Eleven trials compared proportions of patients with a benefit on the CIBIC-plus scale in each of the groups.6-8 11 19-25 "Benefit" was defined as scores from 1-3, or 1-4—that is, the cut-off point for "benefit" was defined in different ways in the various trials. In all 11 trials, significant differences were reported in at least one of the treatment groups compared with placebo—again favouring treatment with cholinesterase inhibitors. However, in five trials7 19 22 24 25 statistical significance vanished in all dose groups after multiplicity has been corrected for, or after considering exclusion of patients in a worst case scenario.
In 10 trials, other instruments were used to evaluate the primary end point(s). In the trial reported by Mohs et al,12 the primary end point was time in days to reach clinically evident functional decline. Donepezil extended the median time to clinically evident functional decline by five months compared with placebo. The AD2000 Collaborative Group15 used as primary end points entry to institutional care and progression of disability. No significant differences were seen in either primary end point.
Tariot et al13 used the neuropsychiatric inventory30 31 as their endpoint measure. No difference between the donepezil and placebo group was found. Holmes et al16 also used the neuropsychiatric inventory as their endpoint measure. The results show a negative effect of withdrawal of donepezil. Winblad et al14 used the Gottfries-Brane-Steen scale32 and found no difference between donepezil and placebo. In three trials,5 10 17 efficacy of treatment was assessed by means of the clinical global impression of change (CGIC33) scale, which is similar to the CIBIC-plus scale. Agid et al17 reported a difference between the 6 mg rivastigmine and the control group, but significance was lost after correction for multiplicity. Rogers et al5 found no difference, whereas Homma et al10 found a significant difference favouring donepezil.
Corey-Bloom et al18 and R?sler et al20 used the progressive deterioration scale (PDS34) as their primary outcome measure. In both trials, significant differences favouring rivastigmine were reported. In the study by R?sler et al,20 significance was lost after correction for multiplicity.
Methodological quality of the trials
Assessment of methodological quality of the 22 randomised controlled trials brought to attention numerous shortcomings (tables 1 and 2).
Table 1 Methodological shortcomings of 12 randomised controlled trials on donepezil
Table 2 Methodological shortcomings of five randomised controlled trials on rivastigmine and five on galantamine
A common shortcoming is the use of several "primary end points without correction for multiple comparisons (see note in table 1). After correction, two of the five trials on rivastigmine do not show any significant benefit on primary endpoint measures any more.17 19
Missing intention to treat analysis
Another shortcoming is a missing intention to treat analysis, as in 15 of the 22 trials patients were excluded from analysis after randomisation (table 1, "Missing patients,"6 7 9-12 14 17 19 20 22-26). In four trials, the number of participants included in endpoint analyses in each group was not reported at all or only partially.5 8 13 15 Consequently, in these four trials the dimension of potential bias emerging through exclusion of patients cannot even be estimated. Depending on the results, exclusion of patients might become very important when mean differences are calculated between treatment groups, because exclusion of only a few patients with extreme results might change the average results considerably. Unfortunately no information is provided in the reports that would allow the reader to assess the impact of excluding patients after randomisation. Furthermore, the calculation of means might be misleading even if patients are not excluded—for example, if a small proportion of patients benefits largely from treatment, the mean value might indicate an improvement even if treatment is slightly harmful for most.
Incomplete data
The handling of incomplete data (dropouts) constitutes another important problem. In at least eight of the trials6-8 16 23 24 25-26 the last observation carried forward (LOCF) method was used to include dropouts into endpoint analyses. This means that the last evaluation before dropout is defined as the endpoint measure. Since Alzheimer's disease is a progressive illness, early discontinuation of treatment because of side effects will pretend a reduced progression of the disease in endpoint analyses using last observation carried forward. In five trials using this method,6 7 23 25 26 dropout rates tended to be considerably higher in the treatment groups, which must have biased the results substantially. But even if dropout rates are equal in treatment and placebo groups, knowledge of dropout time is important to estimate possible bias. However, the exact time of dropouts is reported in none of the trials.
Different design and methodological flaws
Three studies need to be discussed separately as their design or methodological flaws differ from most of the reviewed trials. Mohs et al12 used as their primary end point the "median time in days to reach clinically evident functional decline," defined as a decline of at least one point in "basic activities of daily living (ADL)" or "instrumental activities of daily living" according to the Alzheimer's disease functional assessment and change scale or an increase in global clinical dementia rating of 1 point or more (all measures compared with baseline). The authors report that investigators were instructed to use these criteria. However, the final decision to remove a patient from the assigned treatment was left to the clinical judgment of the investigator. This is a methodological shortcoming since investigators could employ subjective measures to withdraw patients from the trial. Furthermore, 26% of placebo patients and 28% of donepezil patients discontinued the trial prematurely without reaching the predefined end point, which affects the results considerably. A further shortcoming is the restriction to report clinically evident functional decline over a period of only 48 weeks, although the study lasted for 54 weeks.
The AD2000 Collaborative Group15 used as its primary end points entry to institutional care and, similarly to Mohs et al,12 progression of disability. One important methodological flaw is that the duration of the study was not defined in advance. In addition, the results are presented for the combined groups receiving 5 mg and 10 mg donepezil, although groups should have been tested separately. Therefore this study can neither be used as a proof of inefficacy nor as a proof of efficacy of donepezil.
Holmes et al16 report that patients with Alzheimer's disease and neuropsychiatric symptoms were treated with open label donepezil for 12 weeks. During this treatment phase, patients with poor compliance, adverse events, and deterioration of neuropsychiatric symptoms or cognitive capacity were excluded. The remaining patients were randomised (double blind) between continuation of treatment and withdrawal of drug. The results show a negative effect of withdrawal of donepezil: neuropsychiatric symptoms increased when the drug was withdrawn. However, side effects of drug withdrawal are no proof for the efficacy of donepezil.
Adverse events of cholinesterase inhibitors
As shown in tables 3 and 4, donepezil, rivastigmine, and galantamine caused a broad spectrum of adverse events—nausea, vomiting, diarrhoea, and weight loss were the most common. The tables show the proportions of adverse events observed in patients in whom the difference between the cholinesterase inhibitor and placebo reached significance at the 5% level.
Table 3 Patients with adverse events in the donepezil and placebo groups (actual data because testing for significance is not appropriate for rare effects owing to insufficient power)
Table 4 Patients with adverse events in the trials on rivastigmine and galantamine (actual data because testing for significance is not appropriate for rare effects because of insufficient power)
As adverse events are typical for cholinesterase inhibitors, they can affect the efficiency of blinding, because the raters might be able to guess the patient's treatment.
Discussion
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