IN-VITRO EFFICACY OF LEVOFLOXACIN ALONE OR IN COMBINATION TESTED AGAINST MULTIRESISTANT PSEUDOMONAS-AERUGINOSA STRAINS

Levofloxacin, the S(-) isomer of ofloxacin, demonstrates in vitro acti vity against Pseudomonas aeruginosa. To further characterize this acti vity, levofloxacin was tested against three populations of recent clin ical isolates categorized by their resistance patterns to several othe r anti-pseudomonal agents. Results demonstrate the minimum inhibitory concentrations (MICs) for levofloxacin were generally two- to fourfold higher than for ciprofloxacin. Higher fluoroquinolone MICs were assoc iated with MIC increases in other drugs. Levofloxacin demonstrated cro ss resistance against ciprofloxacin-resistant strains. Combinations of levofloxacin and several co-drugs revealed that the majority of evalu able interactions demonstrated indifferent action. Levofloxacin exhibi ted enhanced activity (additive or degrees of synergy) principally wit h piperacillin, aztreonam, or ceftazidime. The synergy and additive ra te (21 to 30%) compared favorably with the enhanced interactions obser ved with gentamicin combined with piperacillin or ceftazidime (27 to 3 0%). Levofloxacin activity against P. aeruginosa was most comparable t o that of ciprofloxacin, which was applicable against > 90% of strains found to be resistant to other classes of antimicrobial agents.