Study of Memantine in Assessment of Selected Measures of Volumetric Magnetic Resonance Imaging (MRI) and Cognition in Moderate AD (Alzheimer's Disease)

Inclusion Criteria: * Ambulatory male or female patients at least 50 years of age (females at least 2 years postmenopausal) * A diagnosis of probable AD \[according to the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Associations (NINCDS-ADRDA) criteria\] of moderate severity \[Mini-Mental State Examination score between 15 and 20, inclusive\] * On a stable dose of Food and Drug Administration (FDA)-approved acetylcholinesterase inhibitor Exclusion Criteria: * Current Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV) Axis I disorder other than AD * Previous imaging results not consistent with the diagnosis of AD * Modified Hachinski Ischemia Score greater than 4 * Evidence of other neurologic disorders * Inability to participate in MRI testing * No clinically significant systemic disease * A known or suspected history of alcohol or drug abuse in the past 10 years * Taking excluded medication * Previous treatment with commercial memantine