Oral Vancomycin Systemic Absorption
Oral vancomycin is not significantly absorbed systemically and remains localized in the gastrointestinal tract in the vast majority of patients. 1, 2
Standard Absorption Profile
Oral vancomycin is poorly absorbed from the gastrointestinal tract in patients with normal intestinal mucosa, which is precisely why it's effective for treating C. difficile infection while minimizing systemic effects. 3
The FDA label explicitly states that oral vancomycin "is not systemically absorbed" and is "for oral use only" for treatment of colitis. 2
In a prospective study of 57 patients receiving oral vancomycin 125 mg four times daily, 98% (56/57) had no detectable serum vancomycin concentrations, with only one patient showing a transient level of 6.7 μg/ml that subsequently became undetectable. 4
The IDSA/SHEA guidelines confirm that "neither vancomycin nor fidaxomicin is significantly absorbed when orally administered; thus, there are few systemic adverse events associated with these drugs." 1
Clinical Situations Where Systemic Absorption Can Occur
While oral vancomycin typically remains in the GI tract, clinically significant serum concentrations have been reported in specific high-risk situations: 2
High-Risk Factors for Systemic Absorption:
- Inflammatory disorders of the intestinal mucosa (severe colitis, inflammatory bowel disease) 2, 5
- High-dose vancomycin regimens (>500 mg/day) 3, 5
- Prolonged therapy (≥10 days of treatment) 5
- Renal insufficiency or dialysis (creatinine clearance ≤50 mL/min) 2, 5
- ICU admission 5
- Use of vancomycin retention enemas 5
- Severe C. difficile infection 5
Clinical Implications
Because oral vancomycin stays in the gut lumen, it has minimal systemic side effects compared to metronidazole, which is systemically absorbed. 1
Intravenous vancomycin has no effect on C. difficile infection because it is not excreted into the colon in therapeutic concentrations. 6
The FDA label warns that "parenteral administration of vancomycin is not effective for treatment of staphylococcal enterocolitis and C. difficile-associated diarrhea." 2
When to Monitor Serum Levels
Monitoring of serum vancomycin concentrations may be appropriate in specific high-risk scenarios: 2
- Patients with renal insufficiency receiving oral vancomycin
- Patients with severe colitis or inflammatory bowel conditions
- Patients receiving concomitant aminoglycoside antibiotics
- Patients on high-dose regimens (500 mg four times daily)
- Patients requiring prolonged therapy
Important Caveat:
In a pediatric case report, a 2-year-old with severe C. difficile colitis and renal insufficiency developed serum vancomycin levels as high as 17.8 mg/L on oral vancomycin 10 mg/kg, demonstrating that systemic absorption can occur when intestinal inflammation is severe. However, as the colitis improved, subsequent levels showed minimal absorption. 7
Bottom Line
For the vast majority of patients with intact intestinal mucosa, oral vancomycin remains in the GI tract with no clinically relevant systemic absorption. 1, 4 However, in patients with severe intestinal inflammation, renal dysfunction, or receiving high doses, some systemic absorption can occur and monitoring may be warranted. 2, 5