Since 2007, new randomized controlled trials of the cholinesterase inhibitors and memantine have been conducted to treat cognitive symptoms of dementia. The following sections review these new trials in patients with specific dementias (i.e., Alzheimer’s disease, vascular dementia, and other dementias).
Alzheimer’s disease.
The 2007 guideline identifies three cholinesterase inhibitors—donepezil, rivastigmine, and galantamine—that have been approved by the U.S. Food and Drug Administration (FDA) for treatment of mild to moderate Alzheimer’s disease. The guideline notes that donepezil has been approved for severe Alzheimer’s disease. Memantine is approved by the FDA for treatment of moderate to severe Alzheimer’s disease. Available evidence for these medications remains modest.
Several new studies of galantamine are available. In a trial by
Burns and colleagues (2009) of patients with severe Alzheimer’s disease and a mean age of 84 years in a nursing home setting, galantamine was found to have minimal clinical benefit. In this study, participants were randomly assigned to receive galantamine titrated to 24 mg/day (
n=207) or placebo (
n=200); 168 and 161 individuals completed the study, respectively. The patients who received galantamine had improved cognitive function as measured by the Severe Impairment Battery but no benefit on their ability to undertake normal daily activities. Efficacy of galantamine was also not found for patients with mild cognitive impairment without dementia in two 24-month randomized double-blind studies (
Winblad et al. 2008). The first study had 990 subjects, the second 1,058.
Since publication of the 2007 guideline, a 23 mg/day formulation of donepezil, a rivastigmine transdermal patch, and a sustained-release formulation of memantine have become available.
In a randomized, double-blind, multisite study that included 1,371 patients with moderate to severe Alzheimer’s disease (
Farlow et al. 2010), the use of 23 mg/day donepezil did not result in a statistically significant difference from the 10 mg/day dosage on the Clinician Interview-Based Impression of Change Plus (CIBIC+) scale. The higher dose of donepezil was associated with a higher proportion of subjects dropping out of treatment as well as a substantial increase in the rate of adverse events compared with 10 mg/day of donepezil. Thus, in clinical use, the potential cognitive effects of the higher dose of donepezil are unlikely to outweigh the increase in adverse effects. In a subsequent subgroup analysis (
Doody et al. 2012), outcomes in patients already taking memantine were compared with outcomes in patients not taking concomitant memantine. Although donepezil at 23 mg/day was found to provide cognitive benefits over the lower dose of donepezil at week 24, memantine had no additional effect.
A study in patients with severe Alzheimer’s disease assessed the effects of two doses of rivastigmine transdermal patch in a 24-week prospective, randomized, double-blind trial (
Farlow et al. 2013) and investigated the efficacy, safety, and tolerability of 13.3 mg/24 hour dosage as compared with 4.6 mg/24 hour dosage of a rivastigmine patch. Individuals who were randomly assigned to receive 13.3 mg/24 hours (
n=356) showed superior effects on cognition and function at weeks 16 and 24 as compared with individuals who were assigned to receive a 4.6 mg/24 hour patch (
n=360). Overall, rates of completion and rates of adverse effects were similar in the two groups, although treatment discontinuation (except for skin irritation) and most side effects occurred more frequently in the higher-dose group. An additional randomized, double-blind, parallel-group study (
Cummings et al. 2012) examined the effects, tolerability, and safety of the rivastigmine transdermal patch at two different doses in 567 patients with Alzheimer’s disease who exhibited cognitive and functional decline following 24–48 weeks of open-label treatment with 9.5 mg/24 hour rivastigmine patch. There was no cognitive benefit from the change to a 13.3 mg/day dosage of the rivastigmine patch, but there was a statistically significant improvement in the Instrumental Activities of Daily Living domain of the Alzheimer’s Disease Cooperative Study–Activities of Daily Living (ADCS-ADL) in patients receiving 13.3 mg/day as compared with 9.5 mg/24 hours at all study time points. Adverse events occurred in a larger fraction of patients who received the 13.3 mg/24 hour rivastigmine patch as compared with the 9.5 mg/24 hour rivastigmine patch.
The 2007 guideline notes that “currently available data suggest that the combination of a cholinesterase inhibitor plus memantine is more likely to delay symptom progression than a cholinesterase inhibitor alone.” The DOMINO trial conducted by
Howard and colleagues (2012) provides additional information on this issue, but interpretation of the findings is limited by important differences among the groups at baseline and high numbers of dropouts, with different dropout rates among the treatment groups. The study was designed to follow a community sample of 800 patients, but only 295 were enrolled, and many of these participants were excluded from the analyses because of poor treatment adherence. At the end of the study, sample sizes ranged from 20 to 38 per group. Study patients had moderate to severe Alzheimer’s disease and had been treated with donepezil for at least 3 months. They were randomly assigned to continue donepezil, switch to placebo, switch to placebo plus memantine, or continue donepezil and start memantine. Patients for whom donepezil was discontinued showed worsening on the standardized Mini-Mental Examination (sMMSE) and the Bristol Activities of Daily Living Scale (BADLS) compared with patients who continued on donepezil: sMMSE –1.9 points; BADLS +3.0 points. These differences were statistically significant. Patients who received memantine had less pronounced worsening than patients who received placebo: sMMSE +1.2 points and BADLS –1.5 points, values that were also statistically significant. In individuals who continued on donepezil, there was no additional benefit of adding memantine.
In addition, there are two systematic reviews that show at best slight effects or unclear clinical significance of memantine added to cholinesterase inhibitors (
Farrimond et al. 2012;
Muayqil and Camicioli 2012). These reviews did not include the two trials and subanalyses above.
Muayqil and Camicioli (2012) pooled data from 13 studies with a total of 971 patients. Small but statistically significant effect sizes were seen in favor of combination therapy among patients with moderate to severe Alzheimer’s disease on scales of cognition, scales of functional outcomes, and the NPI. The authors noted heterogeneity in scales and patient characteristics and concluded that the clinical significance of their findings is uncertain (
Muayqil and Camicioli 2012).
Farrimond et al. (2012) pooled data from three randomized controlled trials with a total of 1,317 patients. They found that adding memantine to a cholinesterase inhibitor had a small impact on patients’ Clinical Global Impression (CGI) score but no benefit on function. They concluded that clinical relevance of adding memantine “is not robustly demonstrated” (
Farrimond et al. 2012).
A clinical trial cited in the 2007 guideline suggested modest efficacy of memantine for patients with mild to moderate Alzheimer’s disease (
Peskind et al. 2006); however, the guideline notes that “this result is not conclusive and additional trials should be performed.” In more recent studies, memantine was not effective in patients with mild to moderate Alzheimer’s disease. In a 24-week double-blind study,
Bakchine and Loft (2008) randomly assigned 470 patients with mild to moderate Alzheimer’s disease to receive either 20 mg/day memantine (
n=318) or placebo (
n=152); 85% and 91%, respectively, completed the study. After 24 weeks, patients treated with memantine showed numerically significant but clinically insignificant improvement relative to placebo on the Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog) and the CIBIC+. Memantine showed no advantage over placebo in a similar trial by
Porsteinsson and colleagues (2008) in which 433 patients with mild to moderate Alzheimer’s disease were randomly assigned to receive placebo or memantine (20 mg/day) for 24 weeks. Primary outcomes were changes from baseline on the ADAS-Cog and CIBIC+ scores. Similarly, no effect for memantine was found in a randomized placebo-controlled trial of memantine and vitamin E in 613 patients with mild to moderate Alzheimer’s disease (
Dysken et al. 2014), as described in more detail in the section “Alternative Treatments.”
Taken together, the bulk of the evidence on the efficacy and effectiveness of cholinesterase inhibitors and memantine in individuals with Alzheimer’s disease consists of trials of individual medications rather than head-to-head comparator trials. On the basis of the available evidence, one could justify using both memantine and a cholinesterase inhibitor, using memantine alone, or using a cholinesterase inhibitor alone in treating an individual with Alzheimer’s disease.
Vascular dementia.
Because of inconclusive evidence, the 2007 guideline does not specifically recommend cholinesterase inhibitors for patients with vascular dementia; however, it notes that individual patients may benefit from this class of medications. The guideline states that evidence does not support the use of memantine in such patients.
New trials of the cholinesterase inhibitors in patients with vascular dementia have not found them to be effective. For example, a 24-week double-blind, randomized, placebo-controlled study of 710 patients with probable vascular dementia showed no effect of rivastigmine (
Ballard et al. 2008b). Similarly, in a multinational, double-blind, parallel-group clinical trial, 788 patients with probable vascular dementia were randomly assigned to receive galantamine or placebo (
Auchus et al. 2007). Galantamine showed no clear effect on activities of daily living or global functioning.
Kavirajan and Schneider (2007) conducted a meta-analysis of randomized controlled trials of cholinesterase inhibitors and memantine in vascular dementia. Three donepezil, two galantamine, one rivastigmine, and two memantine trials, comprising 3,093 patients taking the study drugs and 2,090 patients taking placebo, met selection criteria. Overall, the donepezil trials showed questionable, not clinically significant, or not statistically significant effects on cognition. This meta-analysis concluded that available evidence does not support use of galantamine, rivastigmine, donepezil, or memantine in vascular dementia.
Dichgans and colleagues (2008) conducted a multicenter, 18-week, placebo-controlled, double-blind, randomized parallel-group trial to determine whether donepezil improves cognition in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL;
N = 168). The primary endpoint was change from baseline in the score on the vascular ADAS-Cog. Donepezil showed no effect in sub-cortical vascular cognitive impairment.
Other dementias.
The 2007 guideline states that cholinesterase inhibitors should be considered for patients with mild to moderate Parkinson’s disease dementia (PDD). Supporting evidence, however, remains weak. The guideline describes a single trial of rivastigmine, leading to an FDA indication for this condition. Donepezil was subsequently studied for PDD in a randomized double-blind trial (
Dubois et al. 2012). In this 24-week study in 550 patients, donepezil had no effect on activities of daily living or behavior. There was also no effect on the protocol-specified analyses of cognition, although post hoc analyses found benefit on some measures of cognitive function.
The 2007 guideline suggests that cholinesterase inhibitors can be considered for patients with dementia with Lewy bodies (DLB) and describes two randomized controlled trials, one of rivastigmine and one of donepezil. An additional trial is now available:
Mori and Kosaka (2012) randomly assigned 140 patients with DLB to receive donepezil or placebo for 12 weeks. Donepezil at 5 and 10 mg/day was superior to placebo on measures of cognitive function and behavior.
The 2007 guideline noted little evidence overall to support the use of any particular agent for frontotemporal dementia (FTD), except for two small trials and two case series showing that either trazodone or one of a variety of selective serotonin reuptake inhibitors may be beneficial in decreasing problematic behaviors or agitation. In a more recent study, 36 patients with behavioral variety FTD and primary progressive aphasia were treated in an open-label fashion with galantamine for 18 weeks and then were randomly assigned to receive an additional 8 weeks of either galantamine or placebo (
Kertesz et al. 2008). Galantamine showed no effect on behavior or language.
Similarly, memantine did not improve cognition in randomized placebo-controlled trials of patients with DLB or PDD (
Aarsland et al. 2009;
Emre et al. 2010). In the study by
Aarsland and colleagues (2009), 72 patients with PDD or DLB were randomly assigned to receive memantine (
n=34) or placebo (
n=38). Sixteen patients did not complete the study because of adverse events (the proportion of withdrawals was similar in both groups). In the study by Emre and colleagues (2010), 199 patients were randomly assigned to treatment; 34 with DLB and 62 with PDD were given memantine, and 41 with DLB and 58 with PDD were given placebo. The study was completed by 159 (80%) patients: 80 in the memantine group and 79 in the placebo group.
In two randomized, double-blind, placebo-controlled trials, memantine was not found to be effective for FTD (
Boxer et al. 2013;
Vercelletto et al. 2011). In the trial by Vercelletto and colleagues (2011), no significant differences were found between patients who received memantine (
n=23) and those who received placebo (
n=26) on the CIBIC+ or on secondary measures of cognitive function or illness burden. In the trial by Boxer and colleagues (2013), patients with FTD and patients with aphasias were randomly assigned to treatment with memantine (
n=33 and 8) or placebo (
n=31 and 8). After 26 weeks, there were no statistically significant differences between the groups on measures of cognitive function or clinical global impression.
A randomized, double-blind, placebo-controlled trial by
Hanney and colleagues (2012) found that memantine is not effective for adults over 40 years of age who have Down’s syndrome and dementia. In this study, 88 patients received memantine and 85 received placebo for 52 weeks. Both groups declined in cognition and function, with no differences between the groups for any outcomes.