In vitro activity of flurithromycin, a novel macrolide antibiotic.

Flurithromycin is an (8,S)-8-fluoroerythromycin isolated from the fermentation broth of Streptomyces erythraeus ATCC 31772, a blocked mutant of a strain producer of erythromycin. Its in vitro antibacterial activity has been determined on recent clinical isolates of respiratory pathogens. The range of MIC for Streptococcus pneumoniae and Streptococcus beta-haemolyticus group A is from 0.0015 to 0.006 microgram/ml, for Haemophilus influenzae from 0.012 to 0.4 microgram/ml, for Staphylococcus aureus from 0.1 to 3.1 micrograms/ml. Its action is bacteriostatic and increases at alkaline pH. Among anaerobes Clostridium perfringens, Bacteroides fragilis, other species of Bacteroides and Peptostreptococcus are particularly susceptible. Flurithromycin also showed some activity on Mycobacterium bovis, M. scrofulaceum and M. phley. The determination of killing curves indicated that in most cases a killing effect was obtained at 4 X MIC. A combination of flurithromycin with ampicillin or doxycycline sometimes was synergic, but more often additive and never antagonistic. The possible interference of flurithromycin on some parameters of the natural system of defense was determined. At concentrations equal to therapeutic levels in blood and tissues, flurithromycin did not influence chemotaxis, phagocytosis, metabolic activation and the killing activity of neutrophils.