Ciprofloxacin, azlocilin, ceftizoxime and amikacin alone and in combination against Gram-negative bacilli in an infected chamber model

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Abstract
Ciprofloxacin, azlocillin, ceftizoxime, and amikacin were studied alone and in combination against six Enterobacteriaceae and six strains of Pseudomonas aeruginosa in an infected chamber model in rabbits simulating a closed space infection. In-vivo results were compared with in-vitro tests of inhibition, killing and synergy. Ciprofloxacin was the most effective single agent, with efficacy against five of the six Enterobacteriaceae when used in low doses, and two of the six pseudomonads when used in high doses. The development of in-vitro resistance to ciprofloxacin was observed during therapy in strains which failed to be eradicated. Ciprofloxacin and azlocillin together was the most effective regimen, with efficacy against eleven of the twelve strains. Synergy, as determined by chequerboard testing, did not correlate with in-vivo outcome. Unlike mezlocillin, azlocillin, ceftizoxime or amikacin, MIC testing of ciprofloxacin was predictive of in-vivo success.