Post-antibiotic effect of levofloxacin and tobramycin alone or in combination with cefepime against Pseudomonas aeruginosa.
BACKGROUND
Levofloxacin and tobramycin, alone and in combination with cefepime, were investigated for their in vitro activities and post-antibiotic effects (PAEs) on Pseudomonas aeruginosa.


METHODS
The in vitro activities of tobramycin and levofloxacin in combination with cefepime were determined by microbroth chequerboard technique against six P. aeruginosa strains that were isolated from patients with bacteremia. The results were interpreted by fractional inhibitory concentration index. To determine the PAEs, P. aeruginosa 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
Three synergistic interactions were observed with cefepime-tobramycin and one with cefepime-levofloxacin combinations against tested strains.No antagonism was observed. Levofloxacin produced a PAE ranging from 1.9 to 4.5 h in a concentration-dependent manner. Similar PAEs were induced by tobramycin (ranging from 1.5 to 3.1 h). However, negative PAE values were obtained with cefepime. In combination, cefepime slightly reduced the PAE of tobramycin and levofloxacin against studied strains.


CONCLUSIONS
The finding of this study may have important clinical implications for the timing of doses during therapy with cefepime, levofloxacin and tobramycin alone and in combination.
Ozbek
Berna
B
Department of Pharmaceutical Microbiology, Faculty of Pharmacy, University of Istanbul, Istanbul, Turkey. bernaozbek @ hotmail.com
Otuk
Gulten
G
D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology*; D016470:Bacteremia / Q000188:drug therapy* / Q000382:microbiology; D000077723:Cefepime; D002511:Cephalosporins / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006801:Humans; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000008:administration & dosage / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification; D013997:Time Factors; D014031:Tobramycin / Q000008:administration & dosage / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D064704:Levofloxacin; D000077723:Cefepime; D015242:Ofloxacin; D014031:Tobramycin