Rifaximin SSD in Dementia Trial

Who May Qualify: - Probable Alzheimer's Disease (AD) or Vascular Dementia (VaD) mild or moderate based on Clinical Dementia Rating Scale. - Males and Females Age ≥ 65 years - Community living with availability of caregiver to accompany participant to study visits and to participate in the study. - Able to consent or legal guardian who can consent (with participant assent). - Legally authorized representative (LAR) and caregiver for the study is the same individual. - Fluency (both participant and caregiver) in written and spoken English to participate in study visits. Who Should NOT Join This Trial: - Dementia not due to AD or VaD - Clinically significant agitation or aggression (requiring treatment with antipsychotic medication) - Delusions and/or hallucinations - Severe psychopathology including major depression - Unstable, severe, or poorly controlled medical conditions evident from physical examination or clinical history - Visual and/or hearing disorder that prevents completion of neuropsychologic evaluations. - Diarrhea - Hypersensitivity to rifaximin, components of rifaximin, - and any rifamycin antimicrobial agent - Antibiotic use in the prior 6 months - Taking medications that interact with Rifaximin. P-glycoprotein (P-gp) inhibitor treatment is permitted as long as the use of P-gp inhibitors is discussed with the investigator. - History of alcohol and/or drug abuse - Participation in another investigational drug trial in the last 30 days Always talk to your doctor about whether this trial is right for you.