In vitro activity of meropenem, imipenem, cefepime and ceftazidime againstPseudomonas 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 carbap enems were more effective in vitro than the cephalosporins: 92.5% of isolat es were susceptible to the former and 77.6% to the latter. Essentially no d ifference was found between meropenem and imipenem. More discrepancies were seen between cefepime and ceftazidime: four of 67 isolates (6.0%) were mor e susceptible to cefepime than to ceftazidime, while eight (11.9%) were mor e susceptible to ceftazidime than to cefepime.