About 65% of patients with severe Alzheimer's Disease (AD) will have symptoms of agitation. There are drawbacks associated with the currently available therapeutic interventions for agitation associated with Alzheimer's Disease. In a recent trial, in the group of patients with moderate to severe AD treated with memantine, there were fewer incidences of agitation. It is hypothesized that memantine will be effective in reducing the symptoms of agitation associated with moderate to severe Alzheimer's Disease.

Inclusion Criteria:

• Moderate to Severe Alzheimer's Disease with a score greater than or equal to 4 on agitation/aggression domain of NPI
• Stable dose of donepezil for 3 months

Exclusion Criteria:

• Other evidence of psychiatric disorders
• Oncologic diagnosis
• Clinically significant gastrointestinal, renal, hepatic, endocrine or cardiovascular disease