[In vitro activity of doripenem and other carbapenems against Pseudomonas aeruginosa].

Doripenem, a new carbapenem, has shown to be more active against Pseudomonas aeruginosa than other carbapenems. The activity of doripenem, imipenem and meropenem was evaluated against 93 P. aeruginosa isolates, by agar dilution and disk diffusion methods. MIC50 and MIC90, were as follows (microg/ml): doripenem, 2 and 4; meropenem, 2 and 8; and imipenem, 4 and 8, respectively. Doripenem MICs were 1 to 3 dilutions lower (i.e. more active) than those for imipenem in 82% of the isolates. In comparison with meropenem, doripenem was 1 to 3 dilutions more active in 50% of the isolates. Forty-nine percent of isolates showed the same MIC for both antibiotics. Resistance percentages for both methods were (dilution/diffusion): imipenem = 7.5%/49.5% and meropenem = 3.2%/9.7%. As the CLSI has not established cut off values for doripenem yet, resistance rates for this antibiotic were estimated by considering (a) the same cut off values for imipenem/meropenem set up by the CLSI, and (b) those suggested by Brown et al. In case (a), resistance rates would be 1.1%/2.2% whereas in case (b) 1.1%/17.2% for agar dilution and disk diffusion, respectively. In scenarios where resistance to carbapenem is based on mechanisms other than carbapenemases, doripenem has a promising future for treating P. aeruginosa infections.