title: Levofloxacin selects fluoroquinolone-resistant methicillin-resistant Staphylococcus aureus less frequently than ciprofloxacin.
abstract: Seventeen methicillin-resistant Staphylococcus aureus (MRSA) with unique genotypes were examined to determine if resistance occurs more frequently with ciprofloxacin or levofloxacin. The mean single-step resistance rate to 4 x MIC of ciprofloxacin was 1.05 x 10(-5) (range <4.82 x 10[-11] to 5.06 x 10[-5]), and that to levofloxacin was 4.03 x 10(-6) (range <3.57 x 10[-13] to 4.10 x 10[-5]) (P < 0.05). When serially passaged, the mean MICs of ciprofloxacin and levofloxacin increased 3.0 +/- 1.5-fold and 1.8 +/- 1.4-fold, respectively (P < 0.05). Only four strains became resistant to levofloxacin, but eight became resistant to ciprofloxacin (P < 0.05). Ciprofloxacin selects resistant MRSA more frequently than levofloxacin.
authors.affiliation: Department of Internal Medicine, University of Kentucky School of Medicine, Lexington 40536-0084, USA. meevan1@pop.uky.edu
authors.forename: M E
authors.initials: ME
authors.lastname: Evans
authors.forename: W B
authors.initials: WB
authors.lastname: Titlow
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D064704:Levofloxacin; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology
chemical_list: D000890:Anti-Infective Agents; D002939:Ciprofloxacin; D064704:Levofloxacin; D015242:Ofloxacin