Study Evaluating TheSafety And Efficacy Of PF-05212377 Or Placebo In Subjects With Alzheimer's Disease With Existing Neuropsychiatric Symptoms On Donepezil

Inclusion Criteria: * Clinical diagnosis of probable AD with supportive brain imaging documentation * Have existing neuropsychiatric symptoms as defined by a score equal or greater than 10 on the NPI at screening, arising from item scores equal or greater than 2 (frequency X severity) on at least 2 domains. * Has been on donepezil (stable dose of 5 mg or 10 mg) for at least four months, with no intent to change such for the duration of the study. Exclusion Criteria: * Demonstrate extreme agitation, physical aggression or violence to themselves, their caregiver, or others, and/or an inability to complete the ADAS-cog assessment at Screening. * Have major structural brain disease other than Alzheimer's Disease * Other severe acute or chronical medical or psychiatric condition or laboratory abnormality