Post-antibiotic effect of ceftazidime, ciprofloxacin, imipenem, piperacillin and tobramycin for Pseudomonas cepacia

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Abstract
The post-antibiotic effects (PAE) of ceftazidime, ciprofloxacin, imipenem, piperacillin and tobramycin were studied for ten strains of Pseudomonas cepacia isolated from patients with cystic fibrosis. Antibiotic concentrations used for exposure were either the MIC of each agent for the sensitive isolates or the recommended sensitivity breakpoint concentrations for the resistant iso1ates After 2 h of exposure, cultures were rapidly diluted 1000-fold to eliminate the antibiotic. Out of the ten isolates, there were eight sensitive to ceftazidime six to ciprofloxacin, six to imipenem, nine to piperacillin and five to tobramycin. All antibiotics tested demonstrated PAE for some isolates of P. cepacia, however, each antibiotic failed to produce a PAE for at least one isolate. The mean PAE was 1·35 h for ceftazidime, 2·38 h for ciprofloxacin, 2·39 h for imipenem, 2·16 h for piperacillin and 1·77 h for tobramycin. Imipenem demonstrated PAE of ≥ 0·5 h for all sensitive isolates tested; ceftazidime, piperacillin, ciprofloxacin and tobramycin demonstrated PAE of ≥ 0·5 h for 6/8, 8/9, 5/6 and 2/5 sensitive isolates, respectively. These data indicate that several antibiotics have significant ( ≥ 0·5 h) PAE for isolates of P. cepacia.

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