Study of DHP1401 in Patients With Mild-moderate Alzheimer's Disease Treated With Donepezil(DRAMA)

Inclusion Criteria: 1. ≥55 and ≤85 years of age 2. Patient who was diagnosed mild to moderate Alzheimer's disease by National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association(NINCDS-ADRDA) or National Institute on Aging-Alzheimer's Association(NIAAA) 3. Korean Mini-Mental State Examination(K-MMSE) score 15 to 26 4. Patient who maintained on donepezil without dose escalation or reduction for at least during 3 months before screening (visit 1) 5. Clinical Dementia Rating(CDR) score 0.5 to 2.0 at screening (visit 1) 6. Written informed consent voluntarily 7. Patient who has a relative/caregiver who support the information of patient's status 8. Patient who are deemed adequate to participate in the clinical trial by the investigator 9. Infertility or patients and his/her spouse consent with contraception during the study period Exclusion Criteria: 1. A diagnosis of vascular dementia or dementia by other cause according to the criteria of the NINCDS-ADRDA 2. Structural brain abnormality or impairment 3. Schizophrenia, depressive disorder and bipolar disorder 4. Any neurological disease except Alzheimer' disease (ex. Parkinson's disease, Huntington's disease, brain tumor, normal-pressure hydrocephalus, progressive supranuclear palsy, seizure disorder, subdural hematoma, multiple sclerosis, epilepsy, delusion and head injury required hospitalization) 5. History of any cancer within previous 5 years 6. History of stroke within previous 2 years 7. Heart failure required medication or interventional treatment including myocardial infarction, valvular heart disease, arrhythmia within previous 1 year 8. Uncontrollable diabetes 9. Uncontrollable hypertension 10. Abnormal liver or kidney function 11. Patient with significant clinical meaning to affect cognitive function 12. Patient who participated in other clinical trial within previous 3 months or has a plan to participate in other clinical trial during study period 13. History of abuse of a drug or alcohol within previous 2 years 14. Patient who has administrated other acetylcholinesterase inhibitors except donepezil within previous 4 weeks 15. Patient who are deemed inadequate to participate in the clinical trial by the investigator(ex. a illiteracy, etc.) 16. History of hypersensitivity reaction to the main ingredient of the investigational drugs 17. Patient who has administrated other drugs except donepezil for dementia treatment (it is possible to enroll after washout for 28 days)