ANTIANAEROBIC ACTIVITY OF THE KETOLIDE RU-64004 COMPARED TO ACTIVITIES OF 4 MACROLIDES, 5 BETA-LACTAMS, CLINDAMYCIN, AND METRONIDAZOLE

Agar dilution methodology (with added Oxyrase in the case of the macro lide group to allow incubation without added CO2) was used to compare the activity of RU 64004, a new ketolide, with the activities of eryth romycin, azithromycin, clarithromycin, roxithromycin, clindamycin, amo xicillin with and without clavulanate, piperacillin with and without t azobactam, metronidazole, and imipenem against 379 anaerobes, Overall, RU 64004 yielded an MIC at which 50% of the isolates are inhibited (M IC50) of 1.0 mu g/ml and an MIC90 of 16.0 mu g/ml, In comparison, MIC( 50)s and MIC(90)s of erythromycin, azithromycin, clarithromycin, and r oxithromycin were 2.0 to 8.0 and > 64.0 mu g/ml, respectively. MICs of macrolides, including RU 64004, were higher for Bacteroides ovatus, F usobacterium varium, Fusobacterium mortiferum, and Clostridium diffici le than for the other species, RU 64004 was more active against gram-p ositive rods and cocci, Prevotella and Porphyromonas spp., and fusobac teria other than F. mortiferum and F. varium than against the Bacteroi des fragilis group. Overall MIC(50)s and MIC(90)s (in micrograms per m illiliter), respectively, of other compounds were as follows: clindamy cin, 1.0 and 16.0; amoxicillin, 4.0 and 64.0; amoxicillin-clavulanate, 0,5 and 4.0; piperacillin, 8.0 and >64.0; piperacillin-tazobactam, 1. 0 and 16.0; metronidazole, 1.0 and 1.0; and imipenem, 0.25 and 1.0.