The effect of amikacin and imipenem alone and in combination against an extended-spectrum β-lactamase–producing Klebsiella pneumoniae strain

In vitro and in vivo activities of amikacin and imipenem alone, and in combination, were studied against an extended-spectrum β-lactamase–producing Klebsiella pneumoniae strain. The strain was in vitro susceptible to both antimicrobials at 105 and 107 CFU/mL. In time–kill studies amikacin, imipenem, and amikacin plus imipenem decreased the bacterial counts; difference between the bactericidal effects was not observed. Chequerboard technique showed no interaction between the tested drugs. Mice infected with 107 CFU/g of the K. pneumoniae were treated by amikacin (15 mg/kg every 8 h), imipenem (40 mg/kg every 4 h), or amikacin plus imipenem for 24 h. Blood bacterial counts in the group treated with amikacin plus imipenem did not differ significantly from the groups treated with amikacin or imipenem alone. Combination of amikacin and imipenem did not demonstrate any advantage over imipenem alone either in vitro or in vivo.