Safety and Efficacy Study Evaluating TRx0237 in Subjects With Behavioral Variant Frontotemporal Dementia (bvFTD)

Inclusion Criteria: * Diagnosis of probable bvFTD * Centrally rated frontotemporal atrophy score of 2 or greater on brain MRI * MMSE ≥20 * Age \<80 years * Modified Hachinski ischemic score of ≤ 4 * Females, if of child-bearing potential, must practice true abstinence or be competent to use adequate contraception and agree to maintain this throughout the study * Subject, and/or, in the case of reduced decision-making capacity, legally acceptable representative(s) consistent with national law is/are able to read, understand, and provide written informed consent * Has one (or more) identified adult caregiver who is willing to provide written informed consent for his/her own participation; is able to read, understand, and speak the designated language at the study site; either lives with the subject or sees the subject for ≥2 hours/day ≥3 days/week; agrees to accompany the subject to each study visit; and is able to verify daily compliance with study drug * If currently 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 (CNS) disorder other than bvFTD * Significant intracranial pathology seen on brain MRI scan * Biomarker evidence of underlying Alzheimer's disease pathology * Expressive language deficits * Meets research criteria for Amyotrophic Lateral Sclerosis or motor neuron disease * Meets diagnostic criteria for probable bvFTD but has a proven mutation producing non-tau, non-TDP-43 pathology * Clinical evidence or history of stroke, transient ischemic attack, significant head injury or other unexplained or recurrent loss of consciousness ≥15 minutes * Epilepsy * Rapid eye movement sleep behavior disorder * Major depressive disorder, schizophrenia, or other psychotic disorders, bipolar disorder, substance (including alcohol) related disorders * Metal implants in the head (except dental), pacemaker, cochlear implants, or any other non-removable items that are contraindications to MRI * Resides in hospital or moderate to high dependency continuous care facility * History of swallowing difficulties * Pregnant or breastfeeding * Glucose-6-phosphate dehydrogenase deficiency * 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 * Preexisting or current signs or symptoms of respiratory failure * Concurrent acute or chronic clinically significant immunologic, hepatic, or endocrine disease (not adequately treated) and/or other unstable or major disease other than bvFTD * Diagnosis of cancer within the past 2 years prior to Baseline (other than basal cell or squamous cell skin cancer or Stage 1 prostate cancer) unless treatment has resulted in complete freedom from disease for at least 2 years * Prior intolerance or hypersensitivity to methylthioninium-containing drug, similar organic dyes, or any of the excipients * Treatment currently or within 90 days before Baseline with any of the following medications (unless otherwise noted): * Tacrine * Amphetamine or dexamphetamine * Clozapine, olanzapine (and there is no intent to initiate therapy during the course of the study) * Carbamazepine, primidone * Drugs for which there is a warning or precaution in the labeling about methemoglobinemia at approved doses * Current or prior participation in a clinical trial as follows: * Clinical trial of a product for cognition within 3 months of Screening (unless confirmed to have been randomized to placebo) * A clinical trial of a drug, biologic, device, or medical food in which the last dose/administration was received within 28 days prior to Baseline