Pilot, Single Center, Open, Trial of Rifaximin in Probable Alzheimer's Disease
Phase: PHASE2
Conditions: Alzheimer's Disease
Sponsor: Duke University

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Protocol Title: Pilot, single center, open, trial of 
rifaximin in probable Alzheimer’s Disease 
 
NCT Number: NCT03856359 
 
Date: September 6, 2019 
 
 

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Synopsis 
 
Title: 
Pilot, single center, open, trial of rifaximin in probable 
Alzheimer’s Disease” version date Sept. 6, 2019 
 
Study Description: 
Pilot trial to examine the relationship between rifaximin 
therapy and change in cognition, serum neuronal markers, 
ammonia levels and gut microbiota in patients with mild to 
moderate Probable Alzheimer’s Disease. 
 
 
Objectives: 
Primary Objective:  To test if rifaximin treatment in 
subjects with AD is correlated with improvement in the 
ADAS-Cog. 
 
Secondary Objective: To test if rifaximin treatment is 
associated with changes in serum amyloid-beta 42, total-
tau, Neurofilament light protein markers, serum pro-
inflammatory markers, ammonia levels and gut microbiota 
in AD subjects.   
 
Endpoints: 
 
 
Primary Endpoints: 
Cognitive domain – Alzheimer’s Disease 
Assessment Scale-Cognitive (ADAS-Cog) 
 
Endpoints: 
 
 
Primary Safety Endpoints will be Adverse Events  
 
 
 
 
 
Secondary Endpoints: 
 
 
 
 
 
Serum neuronal markers: 
 
 
 
 
 
 
Neurofilament light (NF-L) 
 
 
 
 
 
 
Total Tau 
 
 
 
 
 
 
Amyloid-beta 42 
 
 
 
 
 
Serum pro-inflammatory markers: 
 
 
 
 
 
 
Interleukin (IL) 1 beta 
IL 2 
IL 4 
IL 5 
IL 6 
IL 8 
IL 10 
IL 13 
 
 
 
 
 
 
Tumor necrosis factor – alpha 
 
 
 
 
 
 
Gut microbiota 
 
 
 
 
 
Serum Ammonia 
 
Study Population: 
 
Mild to moderate severity of Probable Alzheimer’s Disease 

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Phase:  
 
 
Pilot trial - 2a 
 
Description of  
 
Single Site.  Duke University Health System and affiliated 
senior care facilities  
Sites/Facilities Enrolling 
Participants: 
 
Description of Study  
Subjects will be treated with rifaximin (Xifaxan, 
Intervention:  
 
Salix Pharmaceuticals, Bridgewater, NJ) 550 mg  
 
 
 
 
Orally twice a day for 12 weeks          
 
Study Duration: 
 
Up to 24 months (for recruitment, treatment, data 
analyses) 
 
Participant Duration:  
3 months treatment plus 2 month follow up  
 
 
 
 
 
 
 
Introduction 
 
There is an urgent need to develop novel therapies for Alzheimer's disease (AD). 10% of 
persons over age 65 and up to 50% over age 85 have dementia, with over 30 million 
people affected worldwide. The Food and Drug Administration (FDA) has 
approved cholinesterase inhibitors (Aricept, Exelon, Razadyne), memantine (Namenda), 
and a drug combining a cholinesterase inhibitor and memantine (Namzaric) to treat the 
cognitive symptoms of AD. These medications cannot cure AD or stop it from 
progressing. 
 
  
There has been much speculation for decades regarding the cause of Alzheimer’s 
Disease. Two of the many theories are the focus of our research study. The first theory 
posits that toxic brain concentrations of ammonia play a role in the AD pathophysiology 
(Seiler, 1993). There have, however, been no published trials of using ammonia lowering 
medications for the treatment of AD. The second and more recent theory proposes that 
there is a symbiotic relationship between gut microbiota and brain homeostasis and 
that this relationship is disrupted in patients with AD, possibly due to an imbalance in 
the ratio of pro-inflammatory / anti-inflammatory gut microbiota (De-Paula et al, 2018, 
Cattaneo et al, 2017).  
 
Background 

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Rifaximin is a virtually non-absorbed antibiotic with the unique properties of lowering 
blood ammonia levels and altering gut flora. We hypothesize that Rifaximin will improve 
cognition and function in AD patients by lowering blood ammonia and / or lowering 
circulatory pro-inflammatory cytokines secreted by harmful gut bacteria. 
 
We will be measuring blood ammonia levels and pro-inflammatory and anti-
inflammatory compounds in the blood and analyzing gut microbiota in patients with AD 
before and after 3 months of Rifaximin therapy. If patients exhibit measurable 
improvement in cognition and function, we will analyze our data to see if their 
improvement correlates with a lower blood ammonia level and / or a shift towards anti-
inflammatory species in the gut and a similar shift in the blood cytokine panel to 
favoring anti-inflammatory compounds.  
 
Evidence supporting our hypothesis for this study is presented below. 
 
  
Ammonia Neurotoxicity 
 
Ammonia is a substrate as well as a product of 16 different enzymatic reactions in the 
brain. In the healthy brain, ammonia homeostasis is maintained by its combining with 
glutamate to form non-toxic glutamine via the glutamine synthetase pathway. 
In the disease state, high brain ammonia levels adversely affect membrane potential, 
mitochondrial function, astrocyte morphology, energy metabolism, mRNA and protein 
expression, brain pH, calcium signaling and other cellular functions in the brain (Bosoi et 
al, 2009).  
 
The possibility that ammonia is at least partly responsible for the pathologic changes 
seen in the AD brain was first proposed by Seiler in 1993, when he noted that some of 
the changes in the AD brain can also be seen in the brains of hyperammonemic patients 
(Seiler, 1993). The clinical presentation of a patient with high ammonia levels caused by 
congenital portal systemic shunting or an inborn error of metabolism may in fact mimic 
that of dementia (Miyata et al, 2009). Brain PET CT using 13N ammonia showed high 
brain 13N levels, trapped in glutamine, in the brain of patients with hepatic 
encephalopathy, correlating with high peripheral arterial blood ammonia levels (Keiding 
et al, 2005).   
 
Ammonia as a causative factor of AD can be difficult to prove; ammonia levels cannot be 
quantified at autopsy because of rapid post mortem formation of ammonia. However, 
in-vivo studies have shown evidence of elevated ammonia levels in the AD brain. 
Arteriovenous sampling in early stage normoammonemic AD patients demonstrated a 
net release of ammonia (-25.6 micrograms / 100 g x min) from the brain compared to 

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net uptake of ammonia (+7.2 micrograms / 100 g x min) by the brain of young control 
subjects, pointing toward an endogenous source for the ammonia (Hoyer et al, 1990). 
This efflux of ammonia from the AD brain is most likely due to low levels of glutamine 
synthetase found in the AD brain (LePrince et al, 1995), causing high levels of this 
endogenous ammonia to build up in the extracellular fluid and diffuse across the blood 
brain barrier into the venous effluent. Low glutamine synthetase levels have been found 
to correlate with increased density of amyloid deposits in the AD brain (Le Prince et al, 
1995). 
 
The brain also receives exogenous ammonia, of which the gut is a major source. Fecal 
bacteria produce ammonia by fermenting protein. The aging colon contains a greater 
percentage of protein fermenting bacteria than is seen in the colon of younger patients 
(Woodmansey, 2007, Andrieux et al, 2002). The aging colon also has a longer fecal dwell 
time than that of younger patients, allowing higher levels of ammonia to build up before 
fecal evacuation (Woodmansey, 2007, Andrieux et al, 2002). Gut ammonia is absorbed 
into the portal venous system and detoxified in the liver to form uric acid, which is then 
excreted in the kidneys. The uric acid cycle of the aging liver is less efficient at 
detoxifying ammonia (Marchesini, 1990) allowing higher levels of ammonia to reach the 
systemic circulation. One study reported significantly elevated post prandial blood 
ammonia levels in AD patients when compared with age-matched controls (Fisman et al, 
1985). 
  
The blood brain barrier plays an important role in regulating brain ammonia metabolism 
(Hawkins, 2009). 20-50% of blood ammonia passes the blood brain barrier and is 
converted into glutamine. Glutamine and glutamate are pumped from the extracellular 
fluid into the endothelial cells, where glutamine is partially metabolized to ammonia and 
glutamate. Glutamine and ammonia then diffuse into the blood. 
 
Breakdown of the blood brain barrier in the aging patient begins in the hippocampus, 
the area critical for learning and memory, and this may contribute to cognitive decline 
(Erdo et al, 2017). Gadolinium enhanced Brain MRI has shown that the blood brain 
barrier is more permeable in the aging patient when compared with younger patients 
(Montagne et al 2015). The blood brain barrier in the AD patient is also more permeable 
than that of non-cognitively-impaired age matched controls (Montagne et al, 2015). 
High concentrations of Gadolinium are first seen in the hippocampus, the site 
responsible for memory and learning, both of which are clinically impaired in AD 
patients. 
  
One theory is that the  blood brain barrier allows greater amounts of ammonia into the 
AD brain, triggering or worsening pre-existent changes.  
  
This study aims to lower blood and brain ammonia levels in AD patients by targeting the 
colon. This will be accomplished by administering a virtually non-systemically absorbed 
antibiotic, rifaximin, which is FDA approved for hepatic encephalopathy.  Rifaximin 

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lowers blood ammonia by altering fecal flora by blocking bacterial RNA synthesis and 
also by increasing small bowel glutaminase (Garcovich et al, 2012, Kang et al, 2016).  
 
 
Gut Microbiota Dysbiosis 
 
The gut harbors 95% of the total human microbiome and is made up of more than 5,000 
taxa. A diverse and stable gut microbiota promotes health in humans. Gut species 
remain relatively constant throughout adulthood until the seventh decade, when it 
becomes less diverse, harboring higher numbers of Proteobacteria and lower numbers 
of Bifidobacteria. This change most likely accounts for chronic inflammatory disorders 
seen in the elderly. An imbalance in the gut bacterial species can weaken the intestinal 
barrier and create system wide inflammation via gut lymphoid tissue which comprises 
70% - 80% of the immune system. Blood brain barrier permeability is also altered. The 
gut bacteria secrete pro-inflammatory compounds and neuroactive molecules that 
include serotonin, gamma-aminobutyric acid (GABA), catecholamines and acetylcholine 
which cross the blood brain barrier and cause brain inflammation and brain dysfunction. 
(Sochocka et al). 
 
 
A growing number of pro-inflammatory compounds secreted by gut bacteria and seen in 
patients with AD are being discovered. These include interleukin (IL) – 6, tumor necrosis 
– alpha and the inflammasome complex (NLRP3). A recent study revealed higher 
numbers of Escherichia and Shigella in the gut of amyloid positive AD patients when 
compared with healthy controls and this correlated with higher levels of circulating pro-
inflammatory cytokines. The AD patients also had lower numbers of gut Eubacterium 
rectale and this correlated with lower levels of circulating anti-inflammatory compounds 
than seen in controls. (Cattaneo et al). Other researchers found that a preponderance of 
gut Bacteroides and Blautia and reduced numbers of SMB53 and Dialister correlated 
with elevated levels of brain amyloid CSF biomarkers (Vogte NM et al, 2017). 
Interestingly, Clostridium tyrobutyricum and Bacteroides thetaiotaomicron, have been 
shown to actually increase the integrity of the blood brain barrier by enhancing 
expression of tight junction proteins and helping to maintain brain homeostasis. 
(Braniste et al 2014). 
 
Recent evidence also points to a possibly more direct influence of gut bacteria on the 
brain. Terminal branches of the vagus nerve travel in close proximity to the intestinal 
barrier. Neurotransmitters and neuropeptides secreted by bacteria in the gut have been 
shown to activate vagal nerve ascending fibers, influencing brain function in mice. These 
effects ceased after vagotomy was performed. (Holzer et al 2014, Bravo et al, 2011) 
 
 
 
 

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Risk/Benefit Assessment 
 
Known Risks 
 
Risks of taking rifaximin, as listed on the package insert, are as follows. 
  
Rifaximin is contraindicated in patients with hypersensitivity to rifaximin or rifamycin 
antimicrobials. Hypersensitivity reactions include exfoliative dermatitis, angioneurotic 
edema, and anaphylaxis. Clostridium difficile associated diarrhea is a risk whenever a 
patient is maintained chronically on antibiotics, with complications ranging from mild 
diarrhea to fatal colitis. Drug resistant bacteria can also result from long term use. There 
is increased systemic exposure to rifaximin in patients with severe hepatic impairment 
or in patients who are taking P-glycoprotein inhibitors concomitantly. Regarding use in 
geriatric patients, there were no reported overall differences in the safety of the drug 
when used in patients 65 years of age or over, when compared with younger subjects. 
  
The most common reactions seen in patients taking rifaximin are: 
Peripheral edema 
Nausea 
Dizziness 
Fatigue 
Ascites 
Muscle spasms 
Pruritis 
Abdominal pain 
Anemia 
Depression 
Nasopharyngitis 
Arthralgia 
Dyspnea 
Pyrexia 
Rash 
  
 
Potential Benefits 
  
Possible benefits that the subject may receive include the benefits of free 
medical testing and memory evaluations received at screening and during the 
study.  Rifaximin is being used investigationally in this trial and hence it is not known if 
there will be any cognitive benefits.  However, if there is ammonia toxicity in AD and the 

 pg. 8 
drug were to be effective in lowering ammonia, then the subject may experience 
improvements in cognition.  
 
 
Assessment of Potential Risks and Benefits 
 
The available information suggests that the present clinical study has an acceptable risk-
benefit ratio.  
Regarding the risk of C. difficile Infectious Diarrhea, two large randomized Control Trials 
reported a 0.7% and 1.5% incidence of patients with hepatic encephalopathy taking 
rifaximin for 6 months.  In those trials, all affected patients were at increased risk for 
developing C. diff because of either previous lengthy hospitalizations or long courses of 
antibiotics. (Bass  et al, 2010, Mullen et al, 2014) suggesting the risk will be lower in 
healthy subjects with no such risk factors.  
 
The safety monitoring practices employed by this protocol are adequate to protect the 
subjects' safety and  detect  expected emergent adverse effects. The approximate 
volume of blood (120 mL) planned for collection from each subject over the course of 
the entire study (not including rechecks or extra tests ordered by the PI) presents no 
undue risks to the subjects. 
 
 
Objectives and Endpoints 
 
OBJECTIVES 
ENDPOINTS 
JUSTIFICATION FOR 
ENDPOINTS 
Primary 
 
 
ADAS-Cog is a widely 
used cognitive endpoint in 
AD clinical trials and 
changes on this scale are 
considered clinically 
meaningful 
  
  
Secondary 
 
Serum neuronal markers: 
Neurofilament light (NF-L) 
  
Neurofilament light (NF-
L) is a 68 kDa cytoskeletal 
intermediate filament 

 pg. 9 
OBJECTIVES 
ENDPOINTS 
JUSTIFICATION FOR 
ENDPOINTS 
Total Tau 
Amyloid-beta 42 
 
Serum pro-inflammatory 
markers: 
Interleukin (IL) 1 beta 
IL 2 
IL 4, IL 5 
IL 6 
IL 8 
IL 10 
IL 13 
IL 17 
Gut microbiota 
 
 
 
 
 
 
 
 
protein that is expressed in 
neurons (Mattson et al, 
2017, Rissin et al, 2010). 
Neurofilaments can be 
released in significant 
quantity following axonal 
damage or neuronal 
degeneration. NF-L has 
been shown to associate 
with traumatic brain 
injury, multiple sclerosis, 
frontotemporal dementia 
and other 
neurodegenerative 
diseases. The Simoa NF-
light® assay (2) is a digital 
immunoassay for the 
quantitative determination 
of   NF-L in serum and 
plasma. This ultrasensitive 
assay provides an 
analytical sensitivity of 
0.6 pg/mL (10-fold greater 
than the 78.0 pg/mL for 
the standard ELISA). 
Plasma NFL also 
correlates closely with 
CSF concentrations. 
Tau is a microtubule-
stabilizing protein 
primarily localized in 
central nervous system 
neurons, but is also 
expressed at low levels in 
astrocytes and 
oligodendrocytes (Dage et 
al, 2016). Potential 
movement of elevated 
CSF tau across the blood-
brain barrier presents a 
possibility that 
measurements of tau in 
blood could provide a 

 pg. 10 
OBJECTIVES 
ENDPOINTS 
JUSTIFICATION FOR 
ENDPOINTS 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
convenient peripheral 
window into brain/CSF 
status. Recent reports 
using digital immunoassay 
technology have shown 
elevation in peripheral tau 
associated with hypoxic 
brain injury, concussed 
hockey players, and 
repetitive minimal head 
injury. The Simoa™ 
Human Total Tau assay 
uses a combination of 
monoclonal antibodies 
that react with both 
normal and 
phosphorylated tau. The 
assay recognizes all tau 
isoforms. 
Amyloid beta 42 is a 42 
amino acid proteolytic 
product from the amyloid 
precursor protein that has 
gained considerable 
attention as a biomarker 
correlating with cognitive 
disorders (Janelidze et al, 
2016). Amyloid beta (Aβ) 
peptides (including the 
shorter Aβ38 and Aβ40 
isoforms) are produced by 
many cell types in the 
body but the expression is 
particularly high in the 
brain. Accumulation of 
Aβ occurs in aging and 
and in the 
neurodegenerative 
process. Concentrations of 
Aβ42 in blood are much 
lower than in 
cerebrospinal fluid, 
(typically single pg/mL 

 pg. 11 
OBJECTIVES 
ENDPOINTS 
JUSTIFICATION FOR 
ENDPOINTS 
 
 
 
 
 
 
 
 
 
 
 
 
Blood Ammonia 
range), requiring very high 
analytical sensitivity. 
Serum pro-inflammatory 
molecules have been 
associated with 
Alzheimer’s Disease 
pathology. (Cattaneo et al, 
2017) 
An imbalance in the 
number of pro-
inflammatory (e.g. 
Shigella, Escherichia) and 
anti-inflammatory 
(Eubacterium rectale) 
species in the gut may be 
responsible for an 
increase in the presence 
of circulating 
inflammatory markers 
(Cattaneo et al, 2017). 
 
High ammonia levels in 
the brain may be 
responsible for 
pathological changes seen 
in AD. 
Secondary 
 
Safety and tolerability 
Monitored via interviews, 
clinic visits, and interim 
phone calls. AEs and 
SAEs will be tabulated. 
Patients with AEs will be 
reported as per IRB and 
FDA guidelines.  
 
 
Study Design 

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Overall Design 
We hypothesize that treatment with rifaximin will improve cognition and will change  
serum neuronal markers.  
  
This is an open label pilot study in which we will consent up to 25 subjects in order to 
treat 10 eligible subjects with probable mild to moderate AD. The study is single site 
and non-randomized. The subjects will be given rifaximin 550 mg orally twice daily for 3 
months after evaluation to ensure they have no contraindications.  Subjects at risk for 
drug interactions or tolerability issues may be started and/or maintained on a lower 
dose of 550 mg once a day. Individuals on concomitant drugs which are contraindicated per 
the package insert or in the investigators judgment will be excluded.  Individuals on concomitant 
drugs which are not contraindicated but known to elevate blood levels SIGNIFICANTLY OR 
THOSE WITH MILD AEs (E.G. MILD DIARHEA) WILL receive qd dosing BASED ON CLINICIAN 
JUDGMENT. Consent, demographics, history, list of current medications, clinical and 
safety assessments, MMSE and blood tests (CBC, CMP, TSH, B-12 and Folic acid) will be 
performed at the Screening Visit. Medical history, physical exam, serum neuronal 
biomarkers and cytokines, serum ammonia level, Adverse Events and cognitive testing 
(ADAS-Cog-11) will be performed at the Baseline Visit. A stool sample collection kit will 
also be given to the subject and caregiver at the Baseline Visit, with instructions for use 
and how to get the sample back to the research coordinator. The stool sample will be 
obtained prior the subject taking the study drug. Medical history, physical exam, serum 
neuronal biomarkers and cytokines, serum ammonia level, Adverse Events and cognitive 
testing (ADAS-Cog-11) will be performed at the 3 month endpoint visit.  A stool sample 
collection kit will also be given to the subject and caregiver at the baseline visit and 3 
month Visit with instructions for use and how to get the sample back to the research 
coordinator.  Interim safety checks will occur via phone calls one week after baseline 
and then every 2 weeks until the 3 month visit, which will then be followed by a 5 
month phone call.  Caregivers will be instructed to call the research coordinator or 
the PI (Dr. Suhocki after business hours or on weekends) if any change in stool is 
noticed at any time during the study.  Unscheduled visit/labs may occur if warranted 
for safety based on clinical judgment. Because of a small risk of developing C. difficile up 
to 2 months following the last administration of rifaximin, the subjects will be followed 
for an additional 2 months after the 3 month treatment ends.  Subjects who terminate 
early will receive the 3 month assessment at the time of termination. 
 
 
 
Scientific Rationale for Study Design 
 
This is an open label pilot study designed to provide preliminary evidence on the clinical 
efficacy of rifaximin in improving cognition in AD patients. We will be looking for 
improvement in test scores, changes in serum levels of neuronal markers and cytokines 
and changes in gut microbiota following treatment. We will also be collecting data 

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regarding the safety of long-term use of this non-absorbed antibiotic for this disease. 
This pilot may form the basis for a future larger randomized, double blind controlled 
study to further test this hypothesis.  Statistical analyses will combined subjects on QD and 
BID for analyses as this is a pilot study and both doses may impact gut flora.  In posthoc analyses 
we will put dosing as a covariate to examine dose effects. 
  
 Justification for Dose and Study Population 
 
The rifaximin dosage and route of administration are the same as that used to treat 
hepatic encephalopathy, for which the drug and dosage are FDA approved. The dose will 
remain the same throughout the 3 month study of rifaximin administration unless 
stopped for safety reasons. The dose can be stopped or temporarily reduced for safety 
or tolerability reasons based on clinical judgment. The age and study sample of mild to 
moderate probable AD is similar to that used in AD prior trials.  We will select our 
sample to be medically stable and free of hepatic disease and not having had recent 
antibiotic therapy to minimize risk for C Difficile infection.   
 
End of Study Definition 
 
The end of the study will occur 5 months after baseline testing and first administration 
of the drug. While drug administration will conclude and endpoint testing will be done 
at 3 months, we will continue to follow each subject for an additional 2 months, as C. 
difficile infectious diarrhea can occur up until 2 months after stopping an antibiotic. 
 
 
Study Population 
 
Inclusion Criteria 
 
Subjects who meet the following criteria will be considered eligible to participate in the 
clinical study: 
  
Probable Alzheimer’s disease (National Institute of Neurological Disorders and Stroke 
(NINDS) criteria), mild to moderate severity 
Ages 55-85; both genders 
Mini Mental State Exam (MMSE) scores 10-22 
Willing and able to comply with all scheduled clinic visits. 
Stable medical health 
Has a family or professional caregiver who has regular contact with subject 
Ability to consent or legal guardian who can consent  
Living at home or in a facility 
On no AD therapies or on stable (2 months) concurrent AD therapies 
 
Exclusion Criteria 

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Subjects who meet one or more of the following criteria will not be considered eligible 
to participate in the clinical study: 
  
Past history of C diff infection 
Individuals on concomitant drugs which are contraindicated per the package insert or in the 
investigators judgment will be excluded 
Assessment, laboratory examination, physical examination or any other medical 
condition or   circumstance making the volunteer unsuitable for participation in the 
study in the judgment of the study clinicians 
Allergy to Rifaximin 
Antibiotic use  in the last 6 months 
Hospitalization in the last 6 months 
Are taking medications that interact with Rifaximin 
Are taking Cyclosporine 
Past or current history of bloody stools or C Diff infection 
Elevated LFTs 
Clinically significant abnormal hepatic or renal function 
Uncorrected thyroid or B12 abnormalities 
Participation in another investigational drug trial in the past 30 days 
History of febrile illness within 5 days prior to the study period 
Hyperammonemia caused by: 
   Valproic acid 
   Chemotherapy 
   Lung transplant        
   Bariatric surgery       
   Ureterosigmoidoscopy 
   Hyperalimentation 
   Urinary tract infection 
   Errors of metabolism 
               Urea cycle 
               Enzyme deficiencies 
               Organic acidemias 
               Fatty acid oxidation 
               Amino acid transport defects 
 
 
Lifestyle Considerations 
 
Participation in the study will not have any impact on subject lifestyle. 
 
 
Screen Failures 
 

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Volunteers who are consented to participate in the clinical trial and who do not meet 
one or more criteria required for participation in the trial during the screening 
procedures will not be rescreened later.  
 
 
Strategies for Recruitment and Retention 
 
 
Subjects will be recruited from referrals and the community via advertisement. 
The study will be posted on clinicaltrials.gov. 
Subjects and caregivers will be compensated for participation in the study at $50 each 
per clinic visit to cover travel and time. 
All tests and drug will be provided at no cost. 
We expect to recruit 1 subject per month. 
 
 
Study Intervention 
 
Study Intervention Description 
 
Rifaximin (Xifaxan, Salix Pharmaceuticals, Bridgewater, N.J.) (See Package Insert) is a 
drug that is approved by the FDA for use in humans for the treatment of Hepatic 
Encephalopathy, Traveler's Diarrhea and Irritable Bowel Syndrome. It is commercially 
available. It will be used in accordance with approved labeling as pertains to dosage and 
administration for Hepatic Encephalopathy, contraindications and warnings. However, it 
will be used investigationally in this trial as rifaximin is not FDA approved for the 
treatment of Alzheimer's Disease. 
  
Safety, Adverse Effects reporting and Management 
The AE monitoring schedule is described in the protocol.  The drug will be discontinued 
immediately if there are emergent signs of C.Difficile (e.g.  patient has watery diarrhea 
for longer than 24 hours,  fever, abdominal pain or  possible bloody stools).  All AEs will 
be assessed by a study physician and referred for appropriate treatment.  The study 
drug may be discontinued at any time per the study physician judgment for safety.   All 
SAEs will be reported to the IRB within 24 hours of becoming aware of the event. 
 
Dosing and Administration 
 
The drug will be administered orally, under supervision of the caregiver, 550 mg twice a 
day, for 3 months.  
 
 
Drug Acquisition and Accountability 

 pg. 16 
 
The drug, rifaximin, will be provided by the study and acquired from the manufacturer. 
Compliance will be monitored at phone calls and accountability through pill counts at 
the endpoint study visit. 
 
 
Formulation, Packaging, Appearance and Labeling 
Rifaximin will be packaged in bottles of 100 tablets of 550 mg. The product will be 
dispensed under the supervision of the study clinician.  
 
 
Product Storage and Stability 
 
Rifaximin will be stored in the clinical study office in a double locked facility in 
conditions suitable for its stability.   
 
 
Preparation 
  
No special measures are required to prepare the drug for oral administration. 
 
 
Measures to Minimize Bias: Randomization and Blinding 
 
This is an open label pilot study.  Objective tests and biomarkers are used to minimize 
bias.  
 
 
Study Intervention Compliance 
 
The subject's caregiver will be asked to keep a log of rifaximin dosage and date and time 
of administration. This will insure compliance and adherence to the study protocol. The 
compliance log and pill count will be reviewed during the endpoint visit. 
 
 
Concomitant Therapy 
 
The subject may take concomitant medications that do not interact with rifaximin. 
These medications will be recorded at baseline. Any new medications taken during the 
study period will be recorded. 
 
 
Rescue Medicine.  AEs will be treated as appropriate with rescue medications.  
 

 pg. 17 
 
 
Participant Discontinuation and Participant Discontinuation / 
Withdrawal 
 
Discontinuation of Study Intervention 
 
Administration of rifaximin will be discontinued and the study will be halted if a subject 
develops a severe hypersensitivity to rifaximin or if a subject develops a C. difficile 
infectious diarrhea with complications or any other AE felt by the clinician to warrant 
discontinuation. 
 
 
Participant Discontinuation / Withdrawal from the Study 
 
While subjects are encouraged to complete all study evaluations, they may withdraw 
from the study at any time and for any reason. Every effort will be made to determine 
why any subject withdraws from the study prematurely. This information will be 
recorded. All subjects who withdraw from the study with an ongoing AE will be followed 
until the event is resolved or deemed stable. If a subject withdraws prematurely, all data 
normally collected at the 3 month Visit will be collected at the time of premature 
discontinuation. Subjects who had to interrupt taking the study drug for any reason may 
be asked to go back on drug if there are no contraindications. Subject participation may 
be terminated prior to completing the study for any of the following reasons: 
Adverse event 
Protocol violation 
Loss to follow up 
Subject withdrew consent at own request 
Other 
 
A Case Report Form (CRF) page will capture the date and the specific underlying reason 
for discontinuation of study intervention or participant discontinuation/withdrawal. 
 
 
Study Assessment and Procedures 
 
Efficacy Assessments 

 pg. 18 
 
 
 
Adverse Event Reporting 
 
 AE reporting will begin at the time of signing of the informed consent (Screening) and 
will continue until discharge from the study (5 months after the first administration of 
rifaximin). 
 
 
Serious Adverse Event Reporting 
 
The PI will notify the IRB of any SAE, whether deemed rifaximin related or not, that a 
subject experiences during their participation in the study within 24 hours of becoming 
aware of the event. Following the end of the subject's 3 month participation in the 
study, the PI will report SAE's spontaneously if considered at least possibly related to 
rifaximin.  SAE reporting will follow Duke IRB requirements.  
Rifaximin Alzheimer’s Disease Study  Pro00093318 
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x 
x 
x 
x 
x 
x 
x 
x 
x 
Phone Assessment 
  
  
x 
x 
x 
x 
x 
x 
  
x 
  
Subject compensation 
  
x 
  
  
  
  
  
  
x 
x 
x 
OnCore Status update 
x 
  
  
  
  
  
  
  
  
x 
  
Phone Screening 
  
  
  
  
  
  
  
  
  
  
  
Bristol Stool Question 
  
x 
  
  
  
  
  
  
x 
  
x 
Unscheduled visit/labs may occur if warranted for safety based on clinical judgment.  

 pg. 19 
  
All SAE's will be followed until satisfactory resolution or until the site investigator deems 
the event to be chronic or the participant is stable.  
  
 
Reporting Events to Participants 
 
Subjects and their caregivers will be informed about individual or aggregate AE's, SAE's 
and study related results as per IRB guidelines.   
 
 
 
Reporting of Pregnancy 
 
NA. Subjects will not be of child bearing age. 
 
 
Definition of Unanticipated Problems 
 
Unanticipated problems in this study will be any AE's or SAE's not previously described 
in other investigators' research with rifaximin or not listed on the package insert for 
rifaximin.  
 
Unanticipated Problem Reporting 
 
Unanticipated problems will be reported to the IRB within 24 hours of its occurrence. 
  
 
Reporting Unanticipated Problems to Participants 
 
Unanticipated problems encountered during the study will be relayed to  the subject(s) 
if relevant to the subject’s safety as deemed appropriate by the Duke IRB. 
 
 
 
Supporting Documentation and Operational Considerations 
 
Regulatory, Ethical and Study Oversight Considerations 
 
Informed Consent Process 
 

 pg. 20 
Before each subject is enrolled in this study, written informed consent will be obtained 
from the subject and/or legally acceptable representative (LAR) according to local IRB 
requirements.   
 
 
 
Abbreviations 
 
AD 
 
 
Alzheimer’s Disease 
AE 
 
 
Adverse Event 
FDA 
 
 
Food and Drug Administration 
IRB 
 
 
Institutional Review Board 
LAR 
 
 
Legally Acceptable Representative 
PI 
 
 
Principle Investigator 
SAE 
 
 
Serious Adverse Event 
US 
 
 
United States 
 
 
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4. Braniste V et al. The gut microbiota influences blood-brain barrier 
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 pg. 23 
https://shared.salix.com/shared/pi/xifaxan550-pi.pdf