Study to Evaluate the Effect and Safety of Quetiapine Extended Release (XR) (FK949E) in Major Depressive Disorder

Inclusion Criteria: * Diagnosis of major depressive disorder as specified in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Text Revision (DSM-IV-TR) with the use of the Mini-International Neuropsychiatric Interview (M.I.N.I.) * Documented appropriate treatment history (i.e., lack of response to treatment at labeled dosage for at least 4 weeks) for the current major depression episode with an antidepressant other than that used concomitantly with the study drug * The Hamilton Depression Rating Scale (HAM-D17) total score of 20 points or more and HAM-D17 depressed mood score of 2 points or more Exclusion Criteria: * Concurrent or previous history of DSM-IV-TR Axis I disorders, except major depressive disorder, within the last 6 months before informed consent * Concurrence of DSM-IV-TR Axis II disorder that is considered to greatly affect patient's current mental status * The duration of the current major depression episode is shorter than 4 weeks or longer than 24 months at informed consent * History of dependence of substances other than caffeine and nicotine or history of abuse or dependence of alcohol * The HAM-D17 suicide score of 3 points or more, history of suicide attempt within the last 6 months before informed consent, or the risk of suicide in the investigator's or subinvestigator's opinion * Concurrent or previous history of diabetes mellitus. HbA1c levels of 6.1% (Japan Diabetes Society values) or more within the past 2 months * Electroconvulsive therapy within the last 62 days before primary registration (within the last 90 days before secondary registration) * Treatment with a depot antipsychotic within the last 28 days * Documented or suspected (to be a carrier of) conditions such as renal failure, hepatic failure, serious cardiac disease (or current use of antiarrhythmic drugs), hepatitis B, hepatitis C, or acquired immunodeficiency syndrome (AIDS) * Concurrence of uncontrolled hypertension (defined as a systolic blood pressure of 180 mmHg or more, or a diastolic blood pressure of 110 mmHg or more at primary registration) or unstable angina that may worsen with the study or may affect the study results based on the clinical judgment of the investigator or subinvestigator * Concurrence of hypotension (defined as a systolic blood pressure of less than 100 mmHg at primary registration) or orthostatic hypotension * Concurrence of malabsorption syndrome, hepatic disease, or other conditions that may affect the absorption and/or metabolism of the study drug * Concurrent or previous history of cerebrovascular disease or transient ischemic attack (TIA) * Known hypersensitivity to quetiapine or any component of FK949E tablets