Comparative activity of metronidazole and tinidazole against Clostridium difficile and Peptostreptococcus anaerobius.

Broth dilution MICs of metronidazole against 38 strains of Clostridium difficile (0.13 microgram/ml) and 11 strains of Peptostreptococcus anaerobius (0.11 microgram/ml) were lower than those of tinidazole (0.16 and 0.17 microgram/ml, respectively). As molar concentrations the nitroimidazoles were equally active. The MICs of the two drugs correlated positively, and the relative activity of tinidazole increased with decreasing susceptibility of both species.