II. Indications

III. Contraindications

  1. Dysentary (febrile, bloody Diarrhea)
  2. Rifamycin allergy (e.g. Rifampin)
  3. Severe liver Impairment (relative, risk of increased Rifaximin exposure)

IV. Mechanism

  1. Oral semisynthetic antibiotic, derived from Rifamycin
  2. Activity primarily limited to the Gastrointestinal Tract (minimal absorption)
  3. Binds Bacterial DNA-dependent RNA Polymerase and inhibits Bacterial RNA synthesis and Bacterial growth
  4. Modifies gut microbiome to reduce Diarrhea

V. Dosing

  1. Traveler's Diarrhea (adults or age >=12 years)
    1. Take 200 mg orally three times daily for 3 days
  2. Hepatic Encephalopathy Prevention
    1. Take 550 mg orally twice daily
  3. Irritable Bowel Syndrome
    1. Take 550 mg orally three times daily for 14 days
    2. May repeat 14 day course up to twice
  4. Clostridioides difficile Receurrence Prevention (not FDA approved, for adults or age >=12 years)
    1. Take 400 mg orally three times daily for 20 days

VI. Adverse Effects

  1. Nausea
  2. Alanine Transaminase (ALT) increase
  3. Secretion red discoloration (urine, sweat, tears)

VII. Safety

  1. Pregnancy Category X in first trimester
    1. Unknown safety beyond first trimester
  2. Unknown Safety in Lactation

VIII. Pharmacokinetics

  1. Minimal absorption
  2. Excreted in stool

IX. Efficacy

  1. Irritable Bowel Syndrome
    1. Improves Abdominal Pain, stool consistency, bloating (NNT 10)
    2. Relapse within 6 months in 50% of patients

X. Drug Interactions

  1. Warfarin
    1. May decrease INR
  2. P-Glycoprotein Inhibitors (e.g. Cyclosporine)
    1. Increase Rifaximin levels

XII. References

  1. Hamilton (2020) Tarascon Pocket Pharmacopoeia
  2. (2021) Irritable Bowel Syndrome Drug Comparison, Presc Lett, #370305
  3. (2020) Med Lett Drugs Ther 62(1594): 41-58

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Cost: Medications

xifaxan (on 1/1/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
XIFAXAN 200 MG TABLET $9.21 each
XIFAXAN 550 MG TABLET $47.68 each