title: Linezolid, levofloxacin, and vancomycin against vancomycin-tolerant and fluoroquinolone-resistant Streptococcus pneumoniae in an in vitro pharmacodynamic model.
abstract: OBJECTIVE
  To compare the pharmacodynamic profiles of linezolid, levofloxacin, and vancomycin against clinical strains of Streptococcus pneumoniae, including vancomycin-tolerant and fluoroquinolone-resistant isolates.
  
  
  METHODS
  In vitro pharmacodynamic model.
  
  
  METHODS
  Biosafety level 2, university research laboratory. BACTERIAL STRAINS: Ciprofloxacin-susceptible (79), ciprofloxacin-resistant (R921), and vancomycin-tolerant (P9802-020) clinical strains of S. pneumoniae.
  
  
  METHODS
  An in vitro pharmacodynamic model was used to simulate standard dosing regimens of linezolid, levofloxacin, and vancomycin against the isolates 79, R921, and P9802-020.
  
  
  RESULTS
  Bacterial density was profiled over 48 hours. Minimum inhibitory concentrations (MICs) for linezolid, levofloxacin, and vancomycin, respectively were 1, 1, 0.5 microg/ml for isolate 79; 1, 4, 0.5 microg/ml for R921; and 0.5, 0.5, 0.5 microg/ml for P9802-020. Vancomycin minimum bactericidal concentration (MBC) values varied across large ranges for the tested strains. Linezolid achieved 99.9% kill against 79 and R921 by 24 and 28 hours, respectively. Levofloxacin achieved 99.9% kill against 79 and P9802-020 by 28 and 4 hours, respectively. Vancomycin achieved 99.9% kill against 79 and R921 by 8 and 24 hours, respectively. Levofloxacin did not demonstrate activity against R921 at the 48-hour end point. Minimal kill (< 2 log) at 48 hours was noted for vancomycin and linezolid against P9802-020. Conclusion. Vancomycin tolerance appeared to be more reliably characterized by persistent viability in time-kill analyses than by MBC:MIC ratios. Vancomycin exhibited bactericidal activity against the non-vancomycin-tolerant strains of S. pneumoniae. Linezolid exhibited both bactericidal and bacteriostatic activity against all three strains tested, whereas levofloxacin demonstrated bactericidal activity against the fluoroquinolone-susceptible isolates. Further investigation of treatment alternatives for infections due to vancomycin-tolerant S. pneumoniae are needed.
authors.affiliation: Anti-Infective Research Laboratory, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: Raymond
authors.initials: R
authors.lastname: Cha
authors.forename: Ronda L
authors.initials: RL
authors.lastname: Akins
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rybak
mesh_terms: D000081:Acetamides / Q000493:pharmacokinetics / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D064704:Levofloxacin; D000069349:Linezolid; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000493:pharmacokinetics / Q000494:pharmacology*; D023303:Oxazolidinones / Q000493:pharmacokinetics / Q000494:pharmacology*; D013296:Streptococcus pneumoniae / Q000187:drug effects*; D014640:Vancomycin / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D023303:Oxazolidinones; D064704:Levofloxacin; D014640:Vancomycin; D015242:Ofloxacin; D000069349:Linezolid