Safety Study of TRx0237 in Patients Already Taking Medications for Mild and Moderate Alzheimer's Disease

Inclusion Criteria * Clinical diagnosis of all cause dementia and probable Alzheimer's disease (AD) * Mini-Mental State Examination (MMSE) score of 14-26 (inclusive) * Cognitive impairment present for at least 6 months * Age ≤90 years * Modified Hachinski ischaemic score of ≤4 * Females, if of childbearing potential, must use adequate contraception and maintain this use throughout participation in the study * Patient is able to read, understand, and provide written informed consent * Has one or more identified caregivers who are able to verify daily compliance with study drug and provide information on safety and tolerability; the caregiver(s) must also give consent to participate * Currently taking an taking an acetylcholinesterase inhibitor and/or memantine; the subject must have been taking such medication(s) for ≥3 months. The dosage regimen must have remained stable for ≥6 weeks and it must be planned to remain stable throughout participation in the study. * Able to comply with the study procedures Exclusion Criteria: * Significant central nervous system disorder other than Alzheimer's disease * Patients in whom baseline MRI is contraindicated such as metal implants in head (except dental), pacemaker, and cochlear implant * Significant focal or intracranial pathology that would lead to a diagnosis other than probable Alzheimer's disease * Clinical evidence or history of stroke, transient ischemic attack, significant head injury or other unexplained or recurrent loss of consciousness * Epilepsy * Major depressive disorder, schizophrenia or other psychotic disorders, bipolar disorder, substance (including alcohol) related disorders * Resides in a hospital or continuous care facility * History of swallowing difficulties * Pregnant or breastfeeding * History of significant hematological abnormality or current acute or chronic clinically significant abnormality * Abnormal serum chemistry laboratory value at Screening deemed to be clinically relevant by the investigator * Clinically significant cardiovascular disease or abnormal assessments * Pre-existing or current signs or symptoms of respiratory failure * Concurrent acute or chronic clinically significant immunologic, renal, hepatic, or endocrine disease (not adequately treated) and/or other unstable or major disease other than Alzheimer's disease * Prior intolerance to methylthioninium-containing drug or any of the excipients * Treatment currently or within 3 months before Baseline with any of the following medications (unless otherwise noted): * Tacrine * Anxiolytics and/or sedatives/hypnotics (exceptions: sedation for MRI or occasional short-acting benzodiazepines, chloral hydrate, or zolpidem as needed at bedtime) * Antipsychotics (clozapine, chlorpromazine, thioridazine, or ziprasidone) * Carbamazepine * Drugs associated with methaemoglobinaemia (e.g., dapsone, local anesthetics such as benzocaine used chronically, primaquine and related antimalarials, sulfonamides) * Warfarin (and other Coumadin derivates such as phenprocoumon) * Current or prior participation in a clinical trial of a drug, biologic, or device in which the last dose was received within 28 days prior to Baseline