TC-5619 as Augmentation Therapy to Improve Cognition in Outpatients With Cognitive Dysfunction in Schizophrenia

Inclusion Criteria: * Diagnosis of schizophrenia, per DSM-IV TR criteria, as aided by the MINI International Neuropsychiatric Interview (MINI) * Controlled schizophrenia, on same dose of quetiapine or risperidone for no less than 2 months prior to screening * Age 18 - 60, male or female * Stable schizophrenia as documented by lack of psychiatric hospitalization for 2 months prior to Screening * Clinical history of stable psychotic symptoms for 1 month prior to Screening * Stable positive symptoms of schizophrenia for 4 weeks prior to Day 1, as shown by score ≤ 4 on PANSS for items related to delusion, hallucination, conceptual disorganization, and unusual thought content, at Screening and at Day 1 * Calgary Depression Scale for Schizophrenia score \< 6 * Outpatient with stable housing, and presence of an informant who sees the subject at least 4 times weekly * Able to understand and sign informed consent Exclusion Criteria: * Diagnosis of schizoaffective or schizophreniform disorders 1 year prior to Screening * Patients at significant risk of suicide or of danger to themselves or others * Antipsychotics other than quetiapine or risperidone, or a change in dosing of these within 2 months of Screening * Treatment with mood stabilizers, antidepressants, or anxiolytics (short-acting hypnotics permitted) * Treatment within 1 month using cognition-affecting agents other than the above, as listed in Appendix 3 (e.g. CNS stimulants) * Use of other prohibited concomitant medications * Other concomitant medications that have been changed within 1 month prior to Screening * History within past 6 months of alcohol or illicit drug abuse * Use of smoking cessation therapy within 1 month prior to Screening * Tobacco users with no detectable urine cotinine level; and tobacco non-users with a detectable urine cotinine level * Unable to comply with study procedures in opinion of investigator, including CogState battery * History of significant other major or unstable neurological, metabolic, hepatic, renal, hematological, pulmonary, cardiovascular, gastrointestinal, or urological disorder * Myocardial infarction * Seizure disorder * Type 1 diabetes mellitus (DM); type 2 DM that requires medication (diet-controlled allowed, with HbA1C \< 7.3) * Electroconvulsive therapy within 2 months prior to Screening * Uncontrolled hypothyroidism, vitamin B12 or folic acid deficiency * Current TB or known systemic infection (HBV, HCV, HIV) * Clinically significant finding on physical exam that could be a safety issue in the study * ALT or AST levels \> 2.5 times the upper limits of the laboratory reference range * Clinically significant lab or ECG abnormality that could be a safety issue in the study, including QTcF \> 450msec (males) or QtcF \> 480msec (females) * Women of child-bearing potential and men unwilling or unable to use accepted methods of birth control * Women with a positive pregnancy test, or who are lactating * Participation in another clinical trial in last 3 months prior to Screening * Involvement in planning or conduct of the study by site staff