Microbial metronidazole metabolism: rat diets for safety testing procedures.

High concentration of metronidazole decrease the nitroreductive activity of the rat's cecal microflora, and preincubation with the drug lowers metabolic activity in vitro. Therefore high doses of metronidazole may lead to a lower yield of potential carcinogenic intermediate(s) in vivo. Since diet influences cecal microbial nitroreductive activity, a combination of diet and dose control may be used to maximize the potential carcinogenicity of the drug in safety evaluation procedures.