• Berna Ozbek and Aylin Sentürk.
• Department of Pharmaceutical Microbiology, Faculty of Pharmacy, University of Istanbul, Beyazit, Istanbul, Turkey. bernaozbek@hotmail.com
• Chemotherapy. 2010 Jan 1; 56 (6): 466-71.

BackgroundColistin 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.MethodsThe 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.ResultsOne 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.ConclusionThis 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.Copyright © 2010 S. Karger AG, Basel.

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