Antimicrobial activity of Ro 23-9424, a novel ester-linked codrug of fleroxacin and desacetylcefotaxime

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Abstract
Ro 23-9424 is a novel ester-linked codrug of fleroxacin (Ro 23-6240; AM-833) and the cefotaxime metabolite desacetylcefotaxime. Its potency was determined against over 1,000 organisms and found to be intermediate between those of the two components. More than 99% of members of the family Enterobacteriaceae were inhibited by greater than or equal micrograms of Ro 23-9424 per ml; its MIC for 50% of strains tested ranged from greater than or equal to 0.06 to 1 micrograms/ml. Staphylococci, streptococci, Branhamella catarrhalis, Corynebacterium jeikeium, Bacillus spp., Haemophilus influenzae, Listeria monocytogenes, and the pathogenic Neisseria spp., including oxacillin-resistant Staphylococcus aureus, beta-lactamase-producing strains, and penicillin-resistant pneumococci, were also inhibited by Ro 23-9424. Pseudomonas aeruginosa, Enterococcus spp., and Bacteroides fragilis group isolates were more refractory to Ro 23-9424 (the MIC for 90% of strains tested was less than or equal to 32 micrograms/ml). Overall, Ro 23-9424 inhibited 97% of the aerobic strains, compared with 90% for ceftazidime and 92% for cefoperazone. Ro 23-9424 was bactericidal, was relatively stable to inoculum effects on MICs at 10(7) CFU/ml, and was determined to be highly active against organisms resistant to fluoroquinolones or ceftazidime. Preliminary quality control guidelines were determined, and a 30-micrograms disk concentration appears to be the most usable form.