Does ertepenem alter the susceptibility of Pseudomonas aeruginosa to carbapenems?

We investigated the effect of ertapenem on carbapenem susceptibility of Pseudomonas aeruginosa. Antibiotic consumption was recorded monthly in defined daily doses (DDD)/100 patient-days in the infectious diseases (ID), abdominal surgery (AS), and surgical intensive care units (SICU) of a teaching hospital from January 2005 to December 2008. Trends of decreased susceptibility of P. aeruginosa were observed in all three units. After the introduction of ertapenem, the number of P. aeruginosa isolates/ 1000 patients-days per month increased in AS and in SICU (p=0.05). The increase in carbapenem non-susceptible isolates/1000 patients-days in the same units was less significant (p=0.07 and p=0.054). Correlations between ertapenem and the carbapenem non-susceptibility for the lagtime of 1 to 6 months ahead gave no significant result. In the SICU, 30% of variability of carbapenem non-susceptibility could be predicted by the consumption of ertapenem. There is no evidence that ertapenem alters the P. aeruginosa susceptibility to carbapenems, but the relationship deserves further observation.