In vitro comparison of the activity of RU 28965, a new macrolide, with that of erythromycin against aerobic and anaerobic bacteria.

RU 28965, a novel macrolide antibiotic, inhibited most gram-positive species at concentrations similar to that of erythromycin but was not active, even at alkaline pH, against Pseudomonas spp. or members of the family Enterobacteriaceae. Staphylococci and streptococci resistant to erythromycin were resistant to RU 28965. RU 28965 inhibited Haemophilus influenzae, including a number of beta-lactamase, ampicillin-resistant isolates, and Neisseria meningitidis and Neisseria gonorrhoeae at concentrations similar to those of erythromycin. Against anaerobic species, Bacteroides fragilis and Clostridia and Fusobacterium spp., RU 28965 was less active than erythromycin, but its activity against Campylobacter and Legionella spp. was similar to that of erythromycin.