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What is this medication?

Rifaximin, Xifaxan (US)/Zaxine (CDN)

Officially indicated to treat hepatic encephalopathy, irritable bowel syndrome without constipation, and traveler’s diarrhea.  It is also prescribed off-label for use in clostridioides difficile infection and small intestinal bacterial overgrowth (SIBO).

How does this medication work?

Rifaximin inhibits bacterial RNA synthesis by binding to bacterial DNA-dependent RNA polymerase.

How should I take this medication?

Clostridioides Difficile Infection (Second or Recurrent)
Oral: Take 400mg three times daily for 20 days; administer after taking a 10-day course of vancomycin.

Hepatic Encephalopathy
Oral: Take 400mg three times daily or 550mg twice daily for 5 to 10 days.

Irritable Bowel Syndrome (without constipation)
Oral: Take 550mg three times daily for 14 days.

Small Intestinal Bacterial Overgrowth (SIBO)
Oral: Take 550mg three times daily for 14 days.  For patients with methane-predominant bacterial overgrowth, some experts use rifaximin as part of an appropriate combination regimen.

Travellers Diarrhea
Oral: Take 200mg three times daily for 3 days.  Avoid in patients with fever or bloody diarrhea.

How to Take: Can be taken with or without food. 

What should I watch for while using this medication?

Use with caution in patients who may have a hypersensitivity reaction to Xifaxan, Zaxine/Rifaxamin.

Prolonged use may result in fungal or bacterial superinfection, including Clostridioides difficile-associated diarrhea (CDAD) and pseudomembranous colitis.

Do Not Take: Avoid using if you have diarrhea with fever and/or blood in the stool.  You need to consider alternative therapy if symptoms persist or worsen after 1 to 2 days of treatment.  Use with caution in cases with severe hepatic impairment.

Do Not Take the Generic Version for SIBO:  Xifaxan/Zaxine is a non-absorbable rifamycin derivative. It is well tolerated and has been demonstrated to be effective in the treatment of SIBO.  Bioavailability studies have shown that the oral absorption is low which is important so that it can act against bacterial synthesis in the small intestine.  A comparison of the generic versus brand name has shown a significantly lower bioavailability for the brand name which is a distinct advantage over its generic counterpart in terms of therapeutic effectiveness.

What if I miss a dose?

If you miss a dose of medication, try to take it as soon as possible.  However, if it is almost time for your next dose, take only that scheduled dose.  Do not take double or extra doses.

How should I store this medication?

Keep out of the reach of children at all times.  Store at room temperature, 59 to 86° F (15 to 30° C).  Protect from light.  Keep the container tightly closed.  Properly dispose of any unused medication after the expiration date.

What are the possible side effects of using this medication?

Frequency of adverse events generally higher following treatment for hepatic encephalopathy. Percentages are presented for cases of hepatic encephalopathy unless otherwise stated.


Cardiovascular: Peripheral edema (15%)

Central Nervous System: Dizziness (13%), fatigue (12%)

Hepatic: Ascites (11%)

Gastrointestinal: Nausea (14%; irritable bowel syndrome with diarrhea 2% to 3%)