Comparative evaluation of the 2-methyl-5-nitroimidazole compounds dimetridazole, metronidazole, secnidazole, ornidazole, tinidazole, carnidazole, and panidazole against Bacteroides fragilis and other bacteria of the Bacteroides fragilis group.

Tube-dilution MICs of seven 2-methyl-5-nitroimidazole compounds varying at the 1-substitution were determined against Bacteroides fragilis. Activities on a molar basis were ranked: tinidazole greater than panidazole greater than ornidazole greater than metronidazole greater than or equal to secnidazole greater than carnidazole greater than dimetridazole. Geometric mean MICs varied from 0.5 to 6.6 microM, and MICs against individual strains varied up to 50-fold between compounds. In general, the MIC of each drug correlated with that of each of the other drugs, but with tinidazole the correlation coefficients tended to be small and were not significant versus metronidazole and secnidazole. MICs against 14 other bacteria of the B. fragilis group, including B. distasonis, B. ovatus, B. thetaiotaomicron, B. uniformis, and B. vulgatus, were within the range determined for B. fragilis.