Response to rivastigmine or donepezil in Alzheimer's patients with symptoms suggestive of concomitant Lewy body pathology

Background: A double-blind randomized trial evaluated the efficacy and tolerability of rivastigmine and donepezil in patients with Alzheimer's disease (AD) over 2 years. Baseline data indicated that some patients had symptoms suggestive of concomitant Lewy body disease. This retrospective analysis investigated whether AD patients with and without symptoms suggesting concomitant Lewy body pathology demonstrated different responses to therapy. Methods: AD patients were divided by the presence/absence of symptoms suggestive of concomitant Lewy body disease. These were identified by a concomitant diagnosis of dementia with Lewy bodies and/or use of anti-parkinsonian medication at baseline. Baseline characteristics, demographics, changes on efficacy parameters and adverse event (AE) frequencies were calculated for rivastigmine- and donepezil-treated patients. Efficacy parameters were the Severe Impairment Battery (SIB), Mini-Mental State Examination (MMSE), Global Deterioration Scale (GDS), Neuropsychiatric Inventory (NPI) and AD Cooperative Study Activities of Daily Living scale (ADCS-ADL). Main efficacy analyses were based on an intent-to-treat last observation carried forward (ITT-LOCF) population. Results: Both populations reached mean doses of rivastigmine and donepezil that were within therapeutic ranges. Nine hundred and ninety-four AD patients received study drug, of whom 49 (4.9%) had symptoms suggestive of concomitant Lewy body disease (25 rivastigmine, 24 donepezil). In this subpopulation, changes from baseline after 2 years of treatment with rivastigmine were significantly better than those seen with donepezil on the SIB, MMSE and ADCS-ADL (ANCOVA or Wilcoxon analyses, p < 0.05, ITT-LOCF). Statistical significance was not maintained in non-ITT-LOCF analyses, except for EP analyses on the SIB and ADCS-ADL (both p < 0.05). Rivastigmine also provided significantly better functioning than donepezil in patients without Lewy body pathology, as shown by a significant treatment difference at endpoint on the ADCS-ADL (p < 0.05, ITT-LOCF; not maintained in non-ITT-LOCF analyses). NPI changes from baseline did not differ significantly between treatment groups. AD patients with symptoms suggestive of concomitant Lewy body disease receiving rivastigmine or donepezil experienced fewer gastrointestinal side effects, leading to fewer discontinuations due to AEs, compared with patients without Lewy body pathology. Conclusion: In this retrospective analysis, AD patients who had symptoms suggestive of concomitant Lewy body disease appeared to show greater treatment responses to rivastigmine than to donepezil, and experienced fewer adverse events under either drug, compared with patients without Lewy body pathology.