A patient with severe Clostridium difficile colitis fails metronidazole therapy. Oral vancomycin is prescribed. Why is intravenous vancomycin ineffective for C. difficile colitis?

• A IV vancomycin does not achieve therapeutic concentrations in the colonic lumen ✓
• B Vancomycin is inactivated by intestinal enzymes when given IV
• C C. difficile has an intrinsic efflux pump that removes IV vancomycin
• D Vancomycin is systemically metabolized to inactive products before reaching the colon

Explanation

Vancomycin is poorly absorbed from the GI tract when given orally, which is why oral administration is used for C. difficile colitis — it delivers high luminal concentrations directly to the site of infection. When given intravenously, vancomycin is distributed systemically but negligible amounts are secreted into the colonic lumen under normal circumstances, making IV dosing ineffective for luminal infection. The drug is not enzymatically inactivated in the gut.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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