A Study of PRX-03140 in Subjects With Alzheimer's Disease Receiving a Stable Dose of Donepezil

Inclusion criteria

* Men or Women with a clinical diagnosis of Probable AD * MMSE score 12 to 22 inclusive * Age \>50 and \<90 years * Received at least 4 months of a stable dose of donepezil 10mg QD for AD * Brain CT or MRI scan Consistent with a primary diagnosis of AD within 24 months * Neurological examination without focal deficits (excluding changes attributable to peripheral nervous system disease, trauma or congenital birth deficits) * No history or evidence of any other CNS disorder that could be interpreted as a cause of dementia * No diagnosis of vascular dementia * No history of significant psychiatric illness such as schizophrenia or bipolar affective disorder. Subjects with major depressive disorder on a stable dose of an antidepressant for \>6 months may be eligible * No evidence of the following: current vitamin B12 deficiency, positive syphilis serology, positive HIV test, or abnormalities in thyroid function * No cognitive rehabilitation within 6 months of the study * Subject has a regular caregiver willing to attend all study visits * Signed informed consent by the subject (and legal guardian, if applicable) * No history of drug or alcohol abuse * No clinically significant laboratory abnormalities or medical history * No investigational drug within 30 days of Randomization * Cannot receive memantine within 2 months of enrollment * No other prescription acetylcholinesterase inhibitors for AD (other than donepezil) within 4 months of enrollment * No clinically significant ECG abnormalities or cardiac history * No history of uncontrolled seizure disorder within 12 months of enrollment * Cannot be taking MAO inhibitors, bupropion,fluoxetine, paroxetine, quinidine * No history of malignancy within 3 years of randomization * Women cannot be pregnant or breastfeeding