title: Postantibiotic effects of tigecycline, colistin sulfate, and levofloxacin alone or tigecycline-colistin sulfate and tigecycline-levofloxacin combinations against Acinetobacter baumannii.
abstract: BACKGROUND
  Colistin sulfate and levofloxacin, alone and in combination with tigecycline, were investigated for their in vitro activities and postantibiotic effects (PAEs) on6 meropenem-resistant Acinetobacter baumannii.
  
  
  METHODS
  The in vitro activities of colistin sulfate and levofloxacin in combination with tigecycline were determined using a microbroth checkerboard technique. The results were interpreted based on the fractional inhibitory concentration index. To determine the PAEs, A. baumannii strains in the logarithmic phase of growth were exposed for 1 h to antibiotics, alone and in combination. Recovery periods of test cultures were evaluated using viable counting after centrifugation.
  
  
  RESULTS
  One synergistic interaction was observed for each of the tigecycline-colistin sulfate and tigecycline-levofloxacin combinations. Colistin sulfate produced a strong PAE ranging from 2.50 to 7.0 h in a concentration-dependent manner. PAEs were induced by levofloxacin (ranging from 0.35 to 2.45 h) and tigecycline (ranging from 0.05 to 1.40 h). In combination, tigecycline slightly changed the PAE of colistin sulfate and levofloxacin against the studied strains.
  
  
  CONCLUSIONS
  This study's findings could have important implications for the timing of doses during antimicrobial therapy with tigecycline, colistin sulfate, and levofloxacin alone and in combination.
authors.affiliation: Department of Pharmaceutical Microbiology, Faculty of Pharmacy, University of Istanbul, Beyazit, Istanbul, Turkey. bernaozbek@hotmail.com
authors.forename: Berna
authors.initials: B
authors.lastname: Ozbek
authors.forename: Aylin
authors.initials: A
authors.lastname: Sentürk
mesh_terms: D000151:Acinetobacter Infections / Q000188:drug therapy / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000302:isolation & purification*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006801:Humans; D064704:Levofloxacin; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D015242:Ofloxacin / Q000494:pharmacology*; D013845:Thienamycins / Q000494:pharmacology; D000078304:Tigecycline
chemical_list: D000900:Anti-Bacterial Agents; D013845:Thienamycins; D064704:Levofloxacin; D000078304:Tigecycline; D015242:Ofloxacin; D000077731:Meropenem; D008911:Minocycline; D003091:Colistin