Antibiotic-Associated Diarrhea: Why It Happens and How to Manage It

Mechanisms

1. Microbiome Disruption – Antibiotics kill commensals → loss of colonization resistance, reduced SCFA production, impaired bile acid metabolism.
2. Osmotic Effect – Unabsorbed carbohydrates (from malabsorption) draw water.
3. Direct Toxicity – Some antibiotics (e.g., clavulanate) stimulate secretion.
4. C. difficile Overgrowth – Toxin-mediated colitis (10–20% of AAD).

Management

• Most AAD mild, self-limited (resolves after course).
• Probiotics (L. rhamnosus GG, S. boulardii) reduce risk ~50%.
• Hydration, BRAT diet.
• If C. diff suspected (watery diarrhea ≥3/day, fever, leukocytosis): stop offending antibiotic, test stool toxin, treat with vancomycin/fidaxomicin.

Prevention

• Narrow-spectrum, shortest effective duration.
• Probiotic co-administration (evidence-based strains).
• Antimicrobial stewardship.