Nuedexta in the Treatment of Pseudobulbar Affect in Patients With Alzheimer's Disease

Inclusion Criteria: * Male/female 55 to 90 years, inclusive. * Meets National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association criteria for probable AD. * Modified Hachinski Ischemia Scale score of ≤4. * Folstein Mini Mental State Exam score 16-26 at Visit 1. * Geriatric Depression Scale score ≤6. For patient with history of depression, he/she have been on steady dose of anti-depressant for at least 3 months. * Clinical history and relevant symptoms of Pseudobulbar Affect. * Center for Neurologic Study-Lability Scale score at baseline ≥13. * Stable hematologic, hepatic, and renal function, with no clinically significant symptoms, and with clinical laboratory results (CBC, clinical chemistry, and urinalysis) up to 1-fold higher than upper limit of normal range. * Resting respiratory rate 12-20/minute. * MRI or CT scan within past 12 months; no findings inconsistent with diagnosis of AD. * ECG (within 4 weeks prior to entry)with no evidence of clinically significant abnormalities. * Concurrent treatment with an acetylcholinesterase inhibitor or memantine allowed; must be on stable dose at least 2 months before screening. Dosing must remain stable throughout the study. * Use of SSRI's allowed. Must have used for 3 months prior to study entry; dose must remain unchanged during course of study. * No current symptoms of depressive disorder. * Score of 19 or lower in the Beck Depression Inventory. * Agrees to use no prohibited medications during study. Exclusion Criteria: * Has current serious or unstable illnesses that, in investigator's opinion, could interfere with analysis of safety and efficacy data; has life expectancy \<2 years. * No reliable caregiver in frequent contact with patient (at least 10 hours/week. * Current or prior history of major psychiatric disturbance. * Have been in other clinical study within 30 days of entry. * Score of 20 or higher in Beck Depression Inventory. * Multiple episodes of head trauma, history within last year of serious infectious disease affecting the brain, head trauma resulting in protracted loss of consciousness, or myasthenia gravis. * Within the last 5 years, history of a primary or recurrent malignant disease. * Known sensitivity to quinidine or dextromethorphan. * History of human immunodeficiency virus, multiple or severe drug allergies, or severe post-treatment hypersensitivity reactions. * History of chronic alcohol or drug abuse/dependence within the past 5 years. * Judged by investigator to be at serious risk for suicide. * Has a recent or current lab result indicating clinically significant lab abnormality. * At Visit 1 has ALT/SGPT values ≥2 times upper limit of normal (ULN); AST/SGOT values ≥3 times the ULN; total bilirubin values ≥2 times the ULN. * Resting diurnal oxygen saturation \<95%. * Received dextromethorphan and quinidine within previous 6 months. * Hypotension (systolic BP \<100 mm Hg); postural syncope; unexplained syncope. * Used medications that affect the CNS (except for AD) for less than 4 weeks. * On disallowed concomitant medications. * Experiencing acute exacerbation of underlying neurological disorder within previous 2 months.