Comparison of Once Daily and Twice Daily Dosing on Safety and Tolerability of Memantine in Patients With Alzheimer

Inclusion Criteria: * The patient has a knowledgeable and reliable caregiver who will accompany the patient to all clinical visits during the study. * The patient has a diagnosis of probable AD consistent with the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria. * The patient has a Mini Mental State Examination (MMSE) score ≥ 5 and ≤ 18 at Screening visit * The dose of Memantine has been stable at 20 mg once a day for at least 3 month prior to screening Exclusion Criteria: * The patient has one or more of the following conditions: Evidence and/or history of any clinically significant neurodegenerative disease or other serious neurological disorders other than Alzheimer's disease including, but not limited to, Lewy body dementia, Fronto-Temporal dementia, Parkinson's disease, Huntington's disease, major cortical stroke, Multiple Sclerosis, major head trauma and primary or secondary cerebral neoplasm. * The patient has a modified Hachinski ischemia score greater than 4 at the screening visit. * The patient has any current psychiatric disorder or Axis I disorder (DSM-IV-TR™ criteria), established as the primary diagnosis, other than AD * The patient is currently receiving treatment with an unstable dose of acetyl cholinesterase inhibitor Other protocol defined inclusion and exclusion criteria may apply