Safety and Efficacy Study of ABT-089 in Adults With Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * Patient has mild to moderate Alzheimer's disease * Patient has been receiving a stable dose of an acetylcholinesterase inhibitor * Patient has a MMSE score between 12 and 26 * Patient has a MHIS score of less than or equal to 4 * Females must be postmenopausal for at least two years or surgically sterile * Patient has an identified, reliable, caregiver who will support him/her to ensure compliance with treatment and will accompany them to each outpatient visit Exclusion Criteria: * Patient is living in a nursing home * Patient has a history of any significant neurologic disease other than Alzheimer's disease * Patient has any uncontrolled medical illness * Patient uses non-prescribed drugs of abuse or has a history of drug or alcohol abuse/dependence