The Efficacy and Safety Study of High Dose Donepezil in Parkinson's Disease With Dementia

Inclusion criteria : * Patients diagnosed as Parkinson's disease according to Queen Brain Bank criteria * Patients who have been diagnosed as dementia after diagnosing Parkinson's disease at least 1 year. * Patients with Hoehn and Yahr staging from 2 to 4 * Patients with MMSE score from 10 to 24 * Patients who have taken donepezil for at least 12 weeks before screening period * Patients whose medications for Parkinson's disease have not change for 1 month * Patients who give informed consent Exclusion criteria : * Patients who cannot be performed neuropsychiatric test because of hearing and visual difficulty * Patients who have taken medicine affecting cognitive function such as anticholinergic drug and memantine -Patients diagnosed as dementia with Lewy body and vascular dementia- * Patients who have history of neurosyphilis, head trauma, encephalitis or other movement disorders * Patients who have psychiatric disease * Except patients who are stable state under antidepressant or atypical neuroleptics * Patients with child-bearing periods * Patients who have severe liver or kidney disease necessary for aggressive treatment * Patients who have gastrointestinal disease needed for treatment * Patients who cannot taken tablet per oral * Patients who are participated in other clinical trial except observational study