Faecal metronidazole concentrations during oral and intravenous therapy for antibiotic associated colitis due to Clostridium difficile.

Faecal metronidazole and hydroxymetronidazole concentrations measured by high pressure liquid chromatography are reported during 10 episodes of Clostridium difficile colitis in nine patients. Bactericidal faecal concentrations were present in all patients with acute disease receiving oral or intravenous metronidazole, and all responded to therapy. Metronidazole and hydroxymetronidazole concentrations fell as the diarrhoea improved and neither substance was detectable in the faeces of five patients after recovery. This demonstration of intracolonic therapeutic concentrations of metronidazole supports the clinical experience of oral metronidazole being effective in the treatment of antibiotic associated diarrhoea caused by C difficile and also suggests a potential role for intravenous metronidazole in this disease.