Standard Dose of Rifaximin for Diarrhea
The standard dose of rifaximin depends on the type of diarrhea: for travelers' diarrhea, use 200 mg three times daily for 3 days; for irritable bowel syndrome with diarrhea (IBS-D), use 550 mg three times daily for 14 days. 1
Dosing by Indication
Travelers' Diarrhea (Acute Infectious Diarrhea)
- 200 mg three times daily for 3 days is the FDA-approved regimen for travelers' diarrhea 1
- This dosing has been validated in multiple randomized controlled trials showing superiority over placebo, with median time to last unformed stool of 32-33 hours versus 60-68 hours with placebo 2, 3
- Higher doses (400 mg three times daily) have been studied but offer no additional clinical benefit over the 200 mg dose 2
Irritable Bowel Syndrome with Diarrhea (IBS-D)
- 550 mg three times daily for 14 days is the FDA-approved dose for IBS-D 4
- The 2022 AGA Clinical Practice Guidelines endorse this regimen based on moderate-quality evidence from phase 3 trials 4
- Patients who respond initially but experience symptom recurrence can be retreated up to 2 times with the same dosage regimen 4
Important Clinical Considerations
Efficacy by Pathogen Type
- Rifaximin is highly effective for noninvasive pathogens, particularly enterotoxigenic E. coli and other noninvasive diarrheagenic bacteria 3
- Rifaximin is less effective for invasive pathogens (Shigella, Campylobacter, Salmonella) compared to fluoroquinolones or azithromycin 3, 5
- If dysentery (bloody diarrhea) or invasive bacterial infection is suspected, azithromycin (1000 mg single dose or 500 mg daily for 3 days) is preferred over rifaximin 5
Pathogen-Negative Diarrhea
- Rifaximin remains effective even when no pathogen is identified on stool culture, suggesting undetected bacterial causes 6
- In pathogen-negative travelers' diarrhea, rifaximin achieved median time to last unformed stool of 33 hours versus 68 hours with placebo 6
Common Pitfalls to Avoid
- Do not use rifaximin for systemic bacterial infections due to minimal systemic absorption (<0.4% bioavailability) 1
- Do not use rifaximin as first-line therapy for suspected invasive diarrhea (fever, bloody stools, severe abdominal pain) - choose azithromycin or a fluoroquinolone instead 5, 3
- Do not exceed 2 retreatment courses for IBS-D, as safety data beyond this are limited 4
Safety Profile
- Adverse events with rifaximin are comparable to placebo across all studied doses 7, 2, 3
- Minimal potential for drug-drug interactions due to negligible systemic absorption 7, 8
- Low risk of Clostridium difficile infection compared to systemically absorbed antibiotics 4
- Exercise caution in patients with severe hepatic impairment (Child-Pugh Class C), as systemic exposure increases 21-fold, though no dose adjustment is recommended 1