The best way to reduce the risk of recurrent CDI is to avoid exposure to systemic antibiotics. However, many patients at risk of recurrent CDI are also at high risk of serious infections which require systemic antibiotics. There is no evidence that oral metronidazole is protective against CDI in patients treated with systemic antibiotics. In fact, there are several reasons for recommending against its use as prophylaxis for CDI.
First, due to its very high bioavailability, concentrations of metronidazole in formed stools are often undetectable (1). Since C. difficile resides primarily in the colon, “preventive” metronidazole in patients at risk of CDI but with formed stools would not be expected to achieve high enough concentrations in the colon to be effective. Metronidazole itself has also been reported to be associated with CDI (1,2). Add to these concerns, the possibility of selection of vancomycin-resistant enterococci, multiple drug-interactions, and adverse effects, and suddenly metronidazole should lose its appeal for CDI prophylaxis.
- Bolton RP, Culshaw MA. Faecal metronidazole concentrations during oral and intravenous therapy for antibiotic associated colitis due to Clostridium difficile. Gut 1986;27:1169-1172.
- Daly JJ, Chowdary KV. Pseudomembranous colitis secondary to metronidazole. Dig Dis Sci 1983;28:573-4.
- Salvatore M, Meyers BR. Metronidazole. In Mandel, Douglas, Bennett’s Principles and Practice of Infectious Diseases-7th Ed. p. 419-426. 2010, Churchill Livingstone, Philadelphia.