Demonstration of in vitro antagonism between fusidic acid and quinolones

Fusidic acid is an antibiotic active against staphylococci and other bacterial pathogens. It is used in the treatment of staphylococcal infections usually in combination with other antibacterial agents. Reports of the clinical effects of antimicrobial combinations containing fusidic acid have been somewhat inconsistent. The aim of this study was to investigate the in vitro antagonism of fusidic acid and quinolones. Twenty-six staphylococci strains isolated from various clinical samples were tested. After detecting the diameter of the zone of inhibition around fusidic acid, levofloxacin, ciprofloxacin, ofloxacin and moxifloxacin for each strain, in vitro antagonism between fusidic acid and each quinolone was investigated using disk approximation. In all 26 strains, quinolones and fusidic acid were antagonist in vitro. The reason for this antagonistic effect and its clinical implications are not known. However, care should be exercised in prescribing quinolones and fusidic acid in combination.