Open-Label Study of Leuco-methylthioninium Bis(Hydromethanesulfonate) (LMTM) in Subjects With Alzheimer's Disease or Behavioral Variant Frontotemporal Dementia (bvFTD)

Inclusion Criteria: * Subjects with all cause dementia and probable Alzheimer's disease at enrollment and who completed participation in one of the following three TauRx studies (inclusive of the 4-week post-treatment follow-up visit): TRx-237-005, TRx-237-008, or TRx-237-015. * Subjects with a diagnosis of probable bvFTD at enrollment and who completed participation in TauRx study TRx-237-007 through Visit 9 (Week 52). * Females, if of child-bearing potential, must practice true abstinence or continue 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 and ethics approval is/are able to read, understand, and provide written informed consent * Has an 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 ≥1 hour/day ≥3 days/week; agrees to accompany the subject to each study visit; and is able to verify daily compliance with study drug * Able to comply with the study procedures Exclusion Criteria: * History of swallowing difficulties * Pregnant or breastfeeding * Clinically significant laboratory, pulse co-oximetry, electrocardiogram, or imaging abnormality (in originating study) or emergent intercurrent illness that, in the judgment of the principal investigator, could result in the risk of participation outweighing the potential benefit * Current participation in, or intent to enroll in, another clinical trial of a drug, biologic, device, or medical food * In Germany, subjects mandated to reside in a continuous care or assisted living facility or those whose willingness to participate in the clinical trial may be unduly influenced