Synergistic interactions of ciprofloxacin and extended-spectrum beta-lactams or aminoglycosides against multiply drug-resistant Pseudomonas maltophilia.

A W Chow,J Wong,K H Bartlett

doi:10.1128/aac.32.5.782

Abstract

The susceptibility of 28 clinical isolates of Pseudomonas maltophilia to 16 antimicrobial agents was determined in vitro by a standard agar dilution method with inoculum sizes of 10(4) and 10(6) CFU. All isolates exhibited multiple drug resistance. Nine isolates were selected for studies of combinations of ciprofloxacin with seven antipseudomonal beta-lactams and three aminoglycosides by a checkerboard agar dilution technique. Synergistic or additive combinations of ciprofloxacin in clinically achievable concentrations were most frequent with mezlocillin (89%), followed by cefoperazone (67%), piperacillin (56%), cefsulodin (56%), and ceftazidime (33%), and were infrequent with aztreonam (11%), the aminoglycosides (0 to 14%), or imipenem (0%). Antagonism was not observed in any combination. These data suggest that combinations of ciprofloxacin with these agents may be useful for some nosocomial multiply drug-resistant P. maltophilia infections.

Highlights

Division of Infectious Diseases, Department of Medicine, University of British Columbia and Vancouver General Hospital, Vancouver, British Columbia VSZ 1M9, Canada
Synergistic or additive combinations of ciprofloxacin in clinically achievable concentrations were most frequent with meziocillin (89%), followed by cefoperazone (67%), piperacillin (56%), cefsulodin (56%), and ceftazidime (33%), and were infrequent with aztreonam (11%), the aminoglycosides (0 to 14%), or imipenem (0%)
Antagonism was not observed in any combination. These data suggest that combinations of ciprofloxacin with these agents may be useful for some nosocomial multiply drug-resistant P. maltophilia infections

Summary

Pseudomonas maltophilia

The susceptibility of 28 clinical isolates of Pseudomonas maltophilia to 16 antimicrobial agents was determined in vitro by a standard agar dilution method with inoculum sizes of 104 and 106 CFU. Synergistic or additive combinations of ciprofloxacin in clinically achievable concentrations were most frequent with meziocillin (89%), followed by cefoperazone (67%), piperacillin (56%), cefsulodin (56%), and ceftazidime (33%), and were infrequent with aztreonam (11%), the aminoglycosides (0 to 14%), or imipenem (0%). Combinations of ciprofloxacin with seven extended-spectrum ,-lactams (imipenem, aztreonam, mezlocillin, piperacillin, ceftazidime, cefoperazone, and cefsulodin) and three aminoglycosides (gentamicin, tobramycin, and amikacin) were examined by a two-dimensional checkerboard agar dilution technique. Our finding that synergistic or additive activity against P. maltophilia was relatively frequent for combinations of ciprofloxacin with mezlocillin, cefoperazone, piperacillin, and cefsulodin at clinically achievable concentrations and, to a lesser extent, with ceftazidime, aztreonam, and aminoglycosides is of considerable interest. B Numbers in parentheses represent the numbers of isolates inhibited at clinically achievable concentrations of the antibiotic combinations

784 NOTES

Findings

LITERATURE CITED