The primary objective is to compare the tolerability between rivastigmine patch monotherapy and combination therapy with memantine in patients with Alzheimer's disease (AD). The secondary objective is to compare the efficacy and safety between rivastigmine patch monotherapy and combination therapy with memantine in patients with AD. The study hypothesis is that the tolerability of the combination therapy with memantine is not inferior to that of rivastigmine patch monotherapy in AD patients.

Recently, the rivastigmine patch demonstrated efficacy comparable to the highest doses of rivastigmine capsules, with markedly improved tolerability profile. We hypothesized that combination of memantine and rivastigmine patch will be safe and well tolerated and result in more clinical benefit in patients with AD in comparison with rivastigmine patch monotherapy, for the mechanisms of the drugs are different.

Inclusion Criteria:

• Dementia by DSM-IV and probable AD by NINCDS-ADRDA
• Age of 50 to 90 years
• Mini-Mental State Examination (MMSE) score of 10 to 20
• Brain MRI or CT scan consistent with a diagnosis of probable AD
• The caregiver must meet the patient at least once a week and be sufficiently familiar with the patient to provide accurate data.
• Ambulatory or ambulatory-aided (is, walker or cane) ability
• Written informed consent will be obtained from the patient (if possible) and from the patient's legally acceptable representative. Even if unable to provide written informed consent, the patient must assent verbally to participating in the study.

Exclusion Criteria:

• Patients with evidence of severe or unstable physical illness, i.e., acute and severe asthmatic conditions, severe or unstable cardiovascular disease, active peptic ulcer disease, severe hepatic or renal disease, or any medical condition which would prohibit them from completing the study
• Any psychiatric or primary neurodegenerative disorder other than AD
• Any patients with hearing or visual problem that can disturb the efficient evaluation of the patients.
• Any patients with a history of drug addiction or alcohol addiction for the past 10 years
• Patients with bradycardia (bpm less than 50) or sick sinus syndrome or conduction defects (sino-atrial block, second ot third degree A-V blocks
• Clinically significant laboratory abnormalities to affect cognitive function (i.e.abnormal thyroid function test, abnormal low level of vitamin B12 or folate, or syphilis, etc)
• History of allergy to topical products containing any of the constitution of the patches
• Current diagnosis of an active skin lesion
• Involved in other clinical trials or treated by experimental drug within 4 weeks
• Patients with hypersensitivity to cholinesterase inhibitors