Rifaximin Duration for Infectious Diarrhea
For acute infectious diarrhea (traveler's diarrhea), rifaximin should be given at 200 mg three times daily for 3 days, but ONLY for non-invasive, watery diarrhea without fever or blood in stool. 1, 2, 3
Critical Limitation: Non-Invasive Pathogens Only
Rifaximin is highly effective for non-invasive pathogens like enterotoxigenic E. coli but should NOT be used for invasive pathogens (Shigella, Campylobacter, Salmonella) where it has documented treatment failures in up to 50% of cases 1, 3
If fever, bloody stools, or dysentery are present, azithromycin (not rifaximin) is the mandatory first-line agent: either 1 gram single dose or 500 mg daily for 3 days 1, 2
Standard Dosing Regimen
The established dose is rifaximin 200 mg three times daily for 3 days for acute watery diarrhea without invasive features 1, 2, 3
This regimen reduces median time to last unformed stool from 65.5 hours (placebo) to 32 hours, demonstrating significant efficacy for appropriate cases 3
The 3-day course is effective even in pathogen-negative diarrhea (38-46% of cases), suggesting undetected bacterial causes 4
When to Choose Azithromycin Instead
For moderate-to-severe diarrhea: azithromycin 500 mg daily for 3 days or 1 gram single dose 1, 2
For dysentery (fever with bloody stools): azithromycin 1 gram single dose is mandatory 1
In Southeast Asia: azithromycin is clearly superior due to >85% fluoroquinolone resistance for Campylobacter, and rifaximin's limitations against invasive pathogens 1
Important Clinical Pitfalls
Never use rifaximin if any of these "red flags" are present: fever, blood in stool, severe abdominal pain, or signs of invasive infection 1, 2, 3
Rifaximin was significantly less effective than ciprofloxacin for invasive intestinal bacterial pathogens in head-to-head trials 3
The safety profile of rifaximin is excellent (similar to placebo), with minimal systemic absorption (<0.4% bioavailability) and low risk of C. difficile infection 5, 6
Combination Therapy Consideration
Loperamide can be combined with rifaximin (4 mg loading dose, then 2 mg after each loose stool, maximum 16 mg/day) to further reduce symptom duration 1, 2
Discontinue loperamide immediately if fever, blood in stool, or severe abdominal pain develops 1
Different Indication: IBS-D
For IBS-D (not acute infectious diarrhea), the dose is completely different: rifaximin 550 mg three times daily for 14 days, with option for up to 2 repeat courses if symptoms recur 7, 8
This higher dose and longer duration for IBS-D should not be confused with the acute infectious diarrhea regimen 7