Can Augmentin Cause Diarrhea?
Yes, Augmentin (amoxicillin-clavulanate) commonly causes diarrhea, with rates ranging from 3-23% depending on the formulation and patient population, making it one of the most frequent adverse effects of this antibiotic. 1
Incidence and Severity
The FDA drug label explicitly lists diarrhea as one of the most common adverse reactions to Augmentin, with rates varying by formulation:
- Augmentin ES-600: Diarrhea occurred in 2.9% of patients, with protocol-defined diarrhea (≥3 watery stools in one day or 2 watery stools per day for 2 consecutive days) affecting 12.9% of pediatric patients 1
- Standard formulations: Diarrhea led to treatment discontinuation in 2.5% of patients 1
Why Clavulanate Matters
The clavulanate component is the primary culprit for diarrhea, not the amoxicillin. A systematic review demonstrated that amoxicillin-clavulanate specifically causes diarrhea (OR 3.30,95% CI 2.23-4.87), while amoxicillin alone does not significantly increase diarrhea risk 2. This finding is critical because:
- The number needed to harm for diarrhea with amoxicillin-clavulanate is only 10 patients (95% CI 6-17) 2
- Studies using reduced clavulanate concentrations (2.85-3.2 mg/kg/day vs standard 6.4 mg/kg/day) showed decreased diarrhea rates from 26% to 17% while maintaining clinical efficacy 3
Population-Specific Risks
Children under 2 years are at highest risk, with diarrhea rates of 18% compared to only 3% in older children 4. The pediatric guideline emphasizes that amoxicillin-clavulanate causes particularly high rates of adverse events, with one study showing 44% of patients experiencing diarrhea, vomiting, rash, or abdominal pain compared to 14% with placebo 5.
Additional Gastrointestinal Effects
Beyond diarrhea, Augmentin can cause:
- Candidiasis (oral/vaginal yeast infections): OR 7.77 (95% CI 2.23-27.11), with number needed to harm of 27 2
- Nausea, vomiting, and indigestion 1
- Rare but serious: pseudomembranous colitis and Clostridioides difficile infection, with amoxicillin-clavulanate showing an OR of 6.05 for CDI risk 6
Clinical Implications
The FDA label warns that pseudomembranous colitis symptoms may occur during or after treatment and should prompt immediate discontinuation 1. The mechanism involves disruption of gut microbiota, with studies showing significant dysbiosis characterized by reduced bifidobacteria and altered bile acid metabolism 7, 8.
Common pitfall: Clinicians often underestimate the frequency of diarrhea with Augmentin. When prescribing, counsel patients that approximately 1 in 10 will develop diarrhea, and this risk is dose-dependent on the clavulanate component, not the amoxicillin.