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 focal or vascular 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; magnetic resonance compatible prosthetics, clips, stents, or any other device proven to be compatible will be allowed
• 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 (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