Optimal use of carbapenems is an important issue in the prevention of resistance in Pseudomonas aeruginosa. In this study, we investigated the correlation between antimicrobial use density (AUD) of carbapenems and imipenem/cilastatin (IPM/CS) or meropenem (MEPM) susceptibility of P. aeruginosa strains. The AUD of five carbapenems [IPM/CS, panipenem/betamipron, biapenem, MEPM and doripenem (DRPM)] was examined every 6 months between 2006 and 2008. The AUD was calculated using the defined daily doses methodology developed by the World Health Organisation. A minimum inhibitory concentration of IPM/CS or MEPM of ≤4 mg/L was considered to be sensitive. There was a significant negative correlation between MEPM susceptibility and the total AUD of MEPM and DRPM [r = -0.823, 95% confidence interval (CI) -0.035 to -0.980; P = 0.044]. Furthermore, there was a significant correlation between MEPM susceptibility and IPM/CS susceptibility (r = 0.839, 95% CI 0.084 to 0.981; P = 0.037). Cross-resistance was therefore investigated and only 5.6% of MEPM-insensitive strains were susceptible to IPM/CS, although 43.3% of IPM/CS-insensitive strains were susceptible to MEPM. These results suggest that curtailing the use of MEPM and DRPM may curb the emergence not only of MEPM-resistant strains but also IPM/CS-resistant strains.
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