Rifaximin: Uses, Mechanism of Action, and Side Effects

Rifaximin is a broad-spectrum, non-absorbable antibiotic widely used in gastrointestinal (GI) disorders. Unlike many antibiotics, rifaximin stays mostly in the gut, making it highly effective for intestinal infections with minimal systemic side effects.

Uses of Rifaximin

Rifaximin is prescribed for several conditions, particularly those related to the gastrointestinal tract:

1. Traveler’s Diarrhea
   • Effective against Escherichia coli and other non-invasive bacteria causing acute diarrhea.
   • Shortens the duration of symptoms.
2. Hepatic Encephalopathy
   • Reduces the recurrence of episodes by decreasing ammonia-producing gut bacteria.
   • Often used along with lactulose.
3. Irritable Bowel Syndrome with Diarrhea (IBS-D)
   • Helps in improving abdominal pain, bloating, and loose stools.
   • Provides symptom relief after short treatment courses.
4. Small Intestinal Bacterial Overgrowth (SIBO)
   • Off-label use to reduce excessive bacterial load in the small intestine.
5. Other Potential Uses
   • Clostridioides difficile (C. diff) infection (as adjunctive therapy).
   • Inflammatory bowel disease (experimental, not standard).

Mechanism of Action (MOA)

• Rifaximin belongs to the rifamycin class of antibiotics.
• It works by irreversibly binding to the β-subunit of bacterial DNA-dependent RNA polymerase.
• This blocks RNA synthesis, thereby inhibiting bacterial protein synthesis.
• Since it is poorly absorbed in the gut, its effect is localized to the gastrointestinal tract.

Side Effects of Rifaximin

Rifaximin is generally well tolerated, but some patients may experience:

• Common side effects
  • Nausea
  • Flatulence
  • Abdominal pain
  • Headache
  • Fatigue
• Less common side effects
  • Fever
  • Peripheral edema
  • Rash or itching
  • C. difficile–associated diarrhea (rare but possible with prolonged use).
• Serious but rare effects
  • Hypersensitivity reactions (angioedema, urticaria)
  • Liver enzyme elevation (monitor in hepatic patients)

Key Takeaway

Rifaximin is a safe and effective antibiotic mainly used in traveler’s diarrhea, hepatic encephalopathy, and IBS-D. Its localized action in the gut makes it unique compared to other antibiotics, with a low risk of systemic side effects. However, careful use is advised to prevent resistance and unnecessary antibiotic exposure.