Yes, Xifaxan (rifaximin) is an antibiotic. The FDA classifies it specifically as a “rifamycin antibacterial,” meaning it belongs to the same chemical family as rifampin, a well-known antibiotic used to treat tuberculosis. What makes Xifaxan unusual is that less than 0.4% of the drug gets absorbed into your bloodstream. Nearly all of it stays in your gut, which is why it’s used for intestinal conditions rather than infections elsewhere in the body.
How Xifaxan Works in the Gut
Xifaxan kills bacteria by blocking an enzyme they need to build proteins. Without that enzyme, bacteria can’t reproduce or survive. Because the drug has broad-spectrum activity against both common and uncommon gut bacteria, including those that produce and don’t need oxygen, it can reshape the bacterial environment in your intestines fairly quickly.
When you take a dose by mouth, about 97% of it passes through your digestive tract and leaves your body in your stool, essentially unchanged. Only a trace amount (around 0.32%) shows up in urine. This gut-only action is the reason Xifaxan causes fewer body-wide side effects than most oral antibiotics, though it doesn’t eliminate them entirely.
What Xifaxan Is Prescribed For
The FDA has approved Xifaxan for three specific conditions:
- Traveler’s diarrhea caused by noninvasive E. coli, in adults and children 12 and older. A typical course is three days.
- Hepatic encephalopathy prevention in adults with liver disease. This is a long-term use, taken twice daily on an ongoing basis to reduce the risk of recurring episodes.
- Irritable bowel syndrome with diarrhea (IBS-D) in adults. A standard course lasts 14 days. If symptoms come back, your doctor can prescribe up to two additional rounds of the same treatment.
Xifaxan is also widely prescribed off-label for small intestinal bacterial overgrowth (SIBO), a condition where excessive bacteria in the small intestine cause bloating, gas, and diarrhea. Studies show a pooled eradication rate of about 71% to 75% for SIBO, and symptoms improved or disappeared in roughly two-thirds of successfully treated patients.
Why It’s Used for Liver Disease
Hepatic encephalopathy happens when a damaged liver can’t filter toxins properly, especially ammonia. Certain bacteria in your colon produce ammonia as a byproduct of breaking down proteins. That ammonia gets absorbed into the bloodstream, travels to the brain, and causes confusion, personality changes, and in severe cases, coma.
Xifaxan reduces the population of these ammonia-producing bacteria in the colon. With fewer bacteria churning out ammonia, less of it reaches the bloodstream, and episodes of encephalopathy become less frequent. For people with advanced liver disease, this can mean the difference between functioning independently and repeated hospitalizations.
Common Side Effects
Because so little of the drug enters your bloodstream, Xifaxan is generally better tolerated than systemic antibiotics. Still, side effects happen. The most commonly reported ones are bloating, gas, stomach pain, constipation, headache, and joint or muscle stiffness. These are typically mild and resolve after the treatment course ends.
Less common side effects include nausea, dizziness when standing up, dry mouth, blurred vision, and loss of appetite. Rarely, people experience allergic reactions with hives, swelling of the face or throat, or skin rash. Xifaxan should not be used if your diarrhea involves fever or blood in the stool, as those symptoms suggest an invasive infection that needs a different type of antibiotic, one that actually reaches the bloodstream.
The Antibiotic Resistance Question
One concern with any antibiotic is whether repeated use breeds resistant bacteria, and Xifaxan is no exception. This is especially relevant for people taking it long-term to prevent hepatic encephalopathy.
A large study published in Nature Communications found that people using rifaximin for hepatic encephalopathy had roughly twice the risk of developing antimicrobial-resistant infections compared to non-users. Within one year, 3.49% of rifaximin users developed a resistant infection versus 1.83% of non-users. The risks were particularly elevated for vancomycin-resistant bacteria (about 2.5 times higher) and multidrug-resistant organisms (about 2.3 times higher).
The mechanism is straightforward: rifaximin exposure can select for bacteria that have mutations making them resistant not only to rifaximin itself but to related antibiotics, including rifampin. Research has also shown that rifaximin can induce cross-resistance to daptomycin, a last-resort antibiotic used for some of the hardest-to-treat infections. People who were already on other antibiotics before starting rifaximin face even greater resistance risks.
None of this means Xifaxan shouldn’t be used. For someone with recurrent hepatic encephalopathy, the immediate benefit of preventing brain-damaging ammonia buildup typically outweighs the resistance risk. But it does underscore that Xifaxan is a real antibiotic with real consequences for your bacterial ecosystem, not a benign supplement you can take casually.
How Xifaxan Differs From Typical Antibiotics
Most antibiotics you’ve taken for a sinus infection, strep throat, or UTI are designed to be absorbed into your blood so they can reach infected tissue throughout the body. Xifaxan does the opposite. Its near-zero absorption is an intentional design feature, not a limitation. It concentrates the drug’s bacteria-killing power exactly where it’s needed: inside the intestinal tract.
This gut-local action means Xifaxan won’t help with pneumonia, a skin infection, or any condition outside the digestive system. It also means it interacts with fewer medications than systemic antibiotics, though you should still let your doctor know what else you’re taking. It can be taken with or without food, which simplifies dosing for people on complex medication schedules.