A 24-weeks, Multi-center, Randomized, Double-blind, Placebo Controlled Study to Evaluate the Efficacy and Safety of Donepezil Hydrochloride in Chinese Subjects With Severe Alzheimer's Disease

Inclusion Criteria * Written informed consent (IC) will be obtained from the subject (if possible) or from the subject's legal guardian or legal representative prior to beginning screening activities. * Subject age range: male and female subjects 50 to 90 years of age, inclusive * Diagnosis: diagnostic evidence of probable Alzheimer's Disease (AD) consistent with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) and National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria * MMSE 1 to 12 inclusive, at both Screening and Baseline * SIB less than or equal to 90 and greater than or equal to 10 at both Screening and Baseline * Comorbid medical conditions must be clinically stable prior to Baseline, unless otherwise specified. Exclusion Criteria * Subjects with a known history of disorders that affect cognition or the ability to assess cognition, but are distinguishable from AD * Evidence of focal disease to account for dementia on any cranial image MRI or CT. * Subjects with dementia complicated by other organic disease or AD with delirium according to DSM-IV criteria * Subjects who cannot swallow or who have difficulty swallowing whole tablets, as tablets should not be broken or crushed * Illiteracy prior to AD * Subjects who are unwilling or unable to fulfill the requirements of the study * Treatment with another cholinesterase inhibitor and/or memantine in the 3 months prior to Screening * Subjects with a poor response (tolerability) to prior exposure to donepezil