LEVOFLOXACIN VERSUS CIPROFLOXACIN, FLUCLOXACILLIN, OR VANCOMYCIN FOR TREATMENT OF EXPERIMENTAL ENDOCARDITIS DUE TO METHICILLIN-SUSCEPTIBLE OR METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

Levofloxacin is the L isomer of ofloxacin, a racemic mixture in which the L stereochemical form carries the antimicrobial activity. Levoflox acin is more active than former quinolones against gram-positive bacte ria, making it potentially useful against such pathogens, In this stud y, levofloxacin was compared to ciprofloxacin, flucloxacillin, and van comycin for the treatment of experimental endocarditis due to two meth icillin-susceptible Staphylococcus aureus (MSSA) and two methicillin-r esistant S, aureus (MRSA) isolates, The four test organisms were susce ptible to ciprofloxacin, the levofloxacin MICs for the organisms were low (0.12 to 0.25 mg/liter), and the organisms were killed in vitro bg drug concentrations simulating both the peak and trough levels achiev ed in human serum (5 and 0.5 mg/liter, respectively) during levofloxac in therapy, Rats with aortic endocarditis were treated for 3 days, Ant ibiotics were injected with a programmable pump to simulate the kineti cs of either levofloxacin (350 mg orally once a day), ciprofloxacin (7 50 mg orally twice a day), flucloxacillin (2 g intravenously four time s a day), or vancomycin (1 g intravenously twice a day), Levofloxacin tended to be superior to ciprofloxacin in therapeutic experiments (P = 0.08), More importantly, levofloxacin did not select for resistance i n the animals, in contrast to ciprofloxacin, The lower propensity of l evofloxacin than ciprofloxacin to select for quinolone resistance was also clearly demonstrated in vitro, Finally, the effectiveness of this simulation of oral levofloxacin therapy was at least equivalent to th at of standard treatment for MSSA or MRSA endocarditis with either flu cloxacillin or vancomycin, This is noteworthy, because oral antibiotic s are not expected to succeed in the treatment of severe staphylococca l infections, These good results obtained with animals suggest that le vofloxacin might deserve consideration for further study in the treatm ent of infections due to ciprofloxacin-susceptible staphylococci in hu mans.