In vitro activity of meropenem, imipenem, cefepime and ceftazidime against Pseudomonas aeruginosa isolates from cystic fibrosis patients

We studied 67 Pseudomonas aeruginosa isolates from cystic fibrosis patients, and compared their in vitro susceptibility to two carbapenems (meropenem and imipenem) and two cephalosporins (cefepime and ceftazidime), The carbapenems were more effective in vitro than the cephalosporins: 92.5% of isolates were susceptible to the former and 77.6% to the latter. Essentially no difference was found between meropenem and imipenem. More discrepancies were seen between cefepime and ceftazidime: four of 67 isolates (6.0%) were more susceptible to cefepime than to ceftazidime, while eight (11.9%) were more susceptible to ceftazidime than to cefepime.