Ciprofloxacin and imipenem alone or in combination in experimental aortic valve endocarditis due to a ciprofloxacin borderline susceptible strain of Pseudomonas aeruginosa

The in vivo efficacies of ciprofloxacin, imipenem and their combination were studied in the rabbit left-sided endocarditis model by using a seroresistant strain of Pseudomonas aeruginosa with borderline susceptibilities to ciprofloxacin (MIC/MBC 1/2 and 2/8 mu g/ml to ciprofloxacin and imipenem, respectively). Both antimicrobials expressed synergy in vitro at the MBC level. Ciprofloxacin was given intramuscularly, 20 mg/kg of body weight q 8 h and imipenem at the same regimen intravenously for 9 days. When compared to the controls no significant differences were observed among the applied regimens regarding (1) blood culture sterilization, (2) percent of sterile vegetation, and (3) mean bacterial titers in vegetations. No strain isolated from vegetations at the end of therapy had developed resistance to either ciprofloxacin or imipenem. It is concluded that further studies are required after appropriate increase of ciprofloxacin dosage and more frequent administration and/or even higher doses of imipenem.