JAC Advance Access published online on November 18, 2002
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkf211
© 2002 by The British Society for Antimicrobial Chemotherapy
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In Brief
1 University of Colorado Health Sciences Center, Antimicrobial
Research Laboratory,
Department of Pharmacy Practice, 4200 E. 9th Ave, Box C238, Denver,
CO 80262, USA
* Corresponding author. E-mail: rose.jung{at}uchsc.edu.
Received 29 April 2002
; revised 12 August 2002
; accepted 20 August 2002
Owing to increasing resistance in Pseudomonas
aeruginosa, empirical drug regimens may include agents to which
some strains may be resistant. The purpose of this study was to
evaluate the in vitro activities of different combinations
of cephalosporin plus fluoroquinolone against P.
aeruginosa isolates with varying susceptibility to the study
drugs. Broth microdilution susceptibility testing was performed
with 10 clinical isolates of P. aeruginosa. The
bactericidal activity of cefepime or ceftazidime alone and in combination
with ciprofloxacin, levofloxacin, gatifloxacin or moxifloxacin was
evaluated using time-kill methods. Colony counts were determined
at 0, 4, 8 and 24 h, using antimicrobial concentrations of 0.5 x MIC. All procedures were performed
in duplicate. Synergy was defined as a >2-log decrease
in cfu/mL at 24 h compared with the single most active agent. The
MICs for tested strains were: ceftazidime 0.75-32, cefepime 0.125-8,
ciprofloxacin 0.0078-8, levofloxacin 0.023-16,
gatifloxacin 0.023-16 and moxifloxacin 0.0521-32
mg/L. Four strains were susceptible to all drugs, two strains were
cephalosporin susceptible and fluoroquinolone resistant, and two
strains were cephalosporin resistant and fluoroquinolone susceptible.
Two strains were resistant or intermediately susceptible to all
drugs. Various cephalosporin and fluoroquinolone combinations were
synergic against P. aeruginosa, including strains
resistant to one or both agents in combination. No synergy was observed
in two strains susceptible to all drugs. There were no differences
noted between different cephalosporin and fluoroquinolone combinations.
Concentrations used in this study are clinically achievable with
recommended regimens in most cases.
Keywords: Pseudomonas aeruginosa, synergy,
fluoroquinolones, cephalosporins
Synergic activity of cephalosporins plus fluoroquinolones
against Pseudomonas aeruginosa with resistance
to one or both drugs
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