The
carbapenem susceptibility of 32 strains of Pseudomonas aeruginosa recently isolated in Kakogawa municipal hospital was investigated. The MIC ranges of
imipenem,
panipenem, and
meropenem were 0.25-16 mg/L, 0.5-16 mg/L, and < 0.03-4 mg/L, respectively, and
meropenem showed the highest antipseudomonal activity among the three
carbapenems tested. In the analysis based on the MIC interpretive standards established by NCCLS, the resistance rates of test strains for
imipenem,
panipenem, and
meropenem were 6.3%, 15.6%, and 0%, respectively. We also investigated the in vitro combined effect of
imipenem or
meropenem with
amikacin against another 20 isolates of P. aeruginosa by checkerboard titration assay. Antagonism (minimum FIC index > 2) was not observed in any combinations against all strains tested. Super-additive effects (minimum FIC index < 1) in the combination of
imipenem and
amikacin were observed in eight (40%) strains tested. In contrast, in the combination of
meropenem and
amikacin, super-additive effects were observed in 14 isolates (70%). These results suggested that
meropenem is superior to
imipenem in combined effect with
amikacin against P. aeruginosa. In conclusion,
meropenem showed higher antipseudomonal activities than other
carbapenems tested in both conditions, alone and in combination with
amikacin. With regard to the clinical efficacy and prevention of antibiotic resistance,
meropenem monotherapy or combination
therapy with
aminoglycoside is the most superior treatment for pseudomonal
infections, and the findings in this study suggest that
meropenem is still clinically very useful.