Abstract
A new macrolide subclass called ketolides, possess a mode of action similar to the macrolide-lincosamide-streptogramin (MLS) compounds. Utilizing reference in vitro tests, the in vitro activity of RU-66647 (a ketolide) was compared to other MLS compounds against 376 Gram-positive organisms and over 400 representative strains of Gram-negative bacilli. The ketolide's spectrum was most similar to clindamycin and an earlier drug in the series (RU-64004 or RU-004) against staphylococci and streptococci. However, RU-66647 was more active than erythromycin and azithromycin against oxacillin-resistant Staphylococcus spp. and vancomycin-resistant enterococci. Ketolide activity was more potent than other MLS drugs against vancomycin-susceptible enterococci (MIC 90′, 3.25–4 μg/ml) and all streptococci (MICs, ⩽0.25 μg/ml). Erythromycin-resistant (constitutive) strains were generally inhibited by ⩽2 μg RU-66647/ml (staphylococci, 31 to 36%; streptococci, 100%; enterococci, 72%). RU-66647 was active against Haemophilus influenzae (MIC 90′, 2 μg/ml), Moraxella catarrhalis (MIC 90, 0.12 μg/ml), and pathogenic Neisseria spp. (MIC 90 0.5 μg/ml). The ketolide failed to inhibit Enterobacteriaceae, nonfermentative Gram-negative bacilli, and Bacteroides fragilis group strains. RU-66647 was observed to be a promising new compound directed toward some organisms resistant to other MLS-class drugs.
Published Version
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