Impact of ertapenem use on Pseudomonas aeruginosa and Acinetobacter baumannii imipenem susceptibility rates: collateral damage or positive effect on hospital ecology?

Results: Mean monthly use of imipenem was 2.9+0.9 DDDs/100 PDs, as compared with 1.2+0.7 DDDs/100 PDs for meropenem and 1.0+0.7 DDDs/100 PDs for ertapenem (after its introduction). After ertapenem adoption, a downward trend was seen in the use of imipenem (P ¼0.016) and ciprofloxacin (P ¼0.004). A total of 6272 Pseudomonas aeruginosa and 1093 A. baumannii isolates were evaluated. Susceptibility of P. aeruginosa to imipenem improved after ertapenem introduction, both according to the proportion of susceptible isolates (P ¼0.002) and to the incidence density of resistance (P ≤0.001). No significant change was seen in A. baumannii susceptibility to imipenem (P¼0.772). By multiple linear regression analysis, the incidence density of imipenem-resistant P. aeruginosa increased with the use of imipenem (P¼0.003) and ciprofloxacin (P ¼0.008). Occurrence of outbreaks (P≤0.001) and use of gentamicin (P¼0.007) were associated with A. baumannii resistance to imipenem. Conclusions: Use of ertapenem was directly associated with a downward trend in the use of imipenem and ciprofloxacin, which may have contributed to improve the susceptibility of P. aeruginosa to imipenem. Ertapenem use had no impact on the susceptibility of A. baumannii to imipenem.