Increased incidence of experimental colon cancer associated with long-term metronidazole therapy

Using the well-established DMH model for colon neoplasia, we demonstrated that a high-fiber diet pair-fed to animals was associated both with certain changes in bacterial profile and with protection against experimental colon neoplasia. The addition of metronidazole on a long-term basis to both high- and low-fiber diets did not alter stool bacteroides counts as expected and was associated with an apparent cocarcinogenic effect. Concern exists among surgeons and gastroenterologists as to whether metronidazole places their patients at risk. The status of long-term metronidazole therapy for patients with Crohn's disease is a pertinent example. In view of our findings, it is important to further elucidate the metabolism of metronidazole in both the rat and human gut.