The in vitro and in vivo effectiveness of amikacin, cefepime, and imipenem was studied using a high inoculum of an extended-spectrum ␤-lactamase-producing Klebsiella pneumoniae strain. An in vitro susceptibility test at the standard inoculum predicted the in vivo outcome of amikacin or imipenem while it did not do so for cefepime due to the inoculum effect.Extended-spectrum ␤-lactamase (ESBL) production is one of the main mechanisms of resistance to ␤-lactam antibiotics among the strains of the family Enterobacteriaceae (14). The therapeutic choices in infections caused by such strains remain limited because of cross-resistance (4). Attempts have been made to compare the activities of ␤-lactams with ␤-lactamase inhibitors, showing inconsistent results (5,20,24,27). Conflicting reports have been published concerning the activities of the broad-spectrum and "fourth generation" cephalosporins with an explanation of the inoculum effect (5,15,27).Our aim was to compare the activities of amikacin, cefepime, amikacin plus cefepime, and imipenem in septic mice infected by an SHV-5 ESBL-producing Klebsiella pneumoniae strain using a high initial inoculum.The SHV-5 ESBL-producing K. pneumoniae strain originated in a premature intensive-care unit (26). Amikacin and cefepime (Bristol-Myers Squibb), imipenem (Merck, Sharp & Dohme), and cisplatin (Ebewe) were used according to the manufacturers' instructions. The MICs and the minimal bactericidal concentrations (MBCs) were determined by the microdilution method with inocula of 10 5 and 10 7 CFU/ml, respectively (20, 21). For the killing curve, the initial bacterial concentration was 8 log 10 CFU/ml. The concentrations of antibiotics chosen were close to the in vivo mean levels in serum: amikacin, 4 g/ml; cefepime, 40 g/ml; amikacin plus cefepime in the same concentrations listed above; and imipenem, 16 g/ml. Synergy was defined as a Ն2-log 10 decrease in the number of CFU per milliliter between the combination and its most active constituent after 24 h (17).Randomly selected male CD-1 mice (30 to 35 g) were used for the pharmacokinetic study, for the determination of blood bacterial counts, and for survival analysis. Each group contained 15 mice. Cisplatin (18 mg/kg of body weight as determined in a pilot study) had been administered by intraperitoneal (i.p.) injection 3 days before infection in order to cause renal impairment (18). The mice were infected i.p. with 10 7 CFU/g; the uninfected group received only cisplatin. Three groups of uninfected mice were used for pharmacokinetic analysis, and they were followed up for 48 h (3,6,9,10,16,19,28). Single doses of amikacin (7.5 mg/kg), cefepime (80 mg/kg), and imipenem (40 mg/kg) were administered i.p. Blood samples were taken 15 and 30 min and 1, 2, and 3 h after drug administration. Antibiotic levels in sera were determined by a paper disk method for imipenem and cefepime with Bacillus subtilis ATCC 6633 and Escherichia coli ATCC 25922, respectively, as indicator organisms on antibiotic medium 1 (Becton Dickinson) (1). The a...

SummaryThe simulation of human serum levels is essential in animal models to extrapolate the experimental results to clinical practice. Administration of a nephrotoxic drug such as cisplatin can be used to cause renal dysfunction as an approach to mimic human serum levels of renally excreted drugs. We aimed to determine the dose of cisplatin that did not affect the survival rate of mice and to achieve human-like serum concentrations of cefepime. Different doses of cisplatin (0, 10, 14, 18, 22 and 26 mg/kg) were given by intraperitoneal (i.p.) injection to mice three days prior to the i.p. administration of 80 mg/kg cefepime. With cisplatin doses of 18 and 22 mg/kg, the half-life of cefepime was significantly prolonged (Po0.001) and all mice survived. The pretreatment with 26 mg/kg cisplatin significantly decreased survival (P ¼ 0.001), but the half-life of cefepime was not significantly longer than of 18 mg/kg cisplatin. Serum levels of cefepime after the pretreatment with 18 mg/kg cisplatin were comparable to published human data. The administration of cisplatin appears to be a suitable method in mice for simulating human serum concentrations of renally excreted drugs.

Activities of ciprofloxacin and levofloxacin against an SHV-5 extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae strain were studied in vitro and in vivo in septic mice using a high inoculum. Susceptibility to ciprofloxacin and levofloxacin was independent of the inoculum size. In killing curve studies, after 24 hours the initial 7.69 log10 CFU/ml increased in the control to 9.34, while it was reduced to 4.83 by ciprofloxacin and to 4.25 by levofloxacin. Mice were infected with 10(7) CFU/g of K. pneumoniae intraperitoneally. Treatment started 2 hours later, when the mean blood bacterial counts were 7.33 log10 CFU/ml, and lasted for 26 hours from the time of infection. Blood bacterial count was reduced from 7.33 log10 CFU/ml to 4.08 log10 CFU/ml by ciprofloxacin (20 mg/kg/6 hours), and to 3.60 log10 CFU/ml by levofloxacin (50 mg/kg/6 hours) 8 hours after the infection, which differed significantly from the infected untreated group. Ciprofloxacin and levofloxacin prolonged significantly the survival of mice compared with the infected untreated group (p<0.001 for both groups). There were not significant differences either in the survival (p=1.0) or in the blood bacterial counts (p=0.216 after 8 hours) between ciprofloxacin and levofloxacin group. Based on these results both ciprofloxacin and levofloxacin could be alternative therapeutic agents for the infection caused by ESBL-producing Klebsiella strains.

No abstract