In-vitro activity of meropenem imipenem, the penem HRE 664 and ceftazidine against clinical isolates from West Germany.

The antibacterial activity in vitro of meropenem was compared with another carbapenem, imipenem, the penem HRE 664, and ceftazidime. MICs were not influenced by pH nor by inoculum size below 5 X 10(5) cfu/ml: higher inocula caused a modest increase in MIC. Cation supplementation of Mueller-Hinton broth was without effect. Meropenem was more active than imipenem and the other comparative agents against the majority of Gram-negative species (in particular proteus, providencia, morganella, haemophilus, neisseria and Pseudomonas aeruginosa, including isolates from patients with cystic fibrosis). Against Gram-positive organisms, the activity of meropenem was equal to or slightly less that of imipenem. Neither meropenem nor imipenem were influenced by the extended spectrum beta-lactamases that confer resistance to third generation cephalosporins produced by Escherichia coli, Klebsiella pneumoniae, K. oxytoca or Serratia marcescens.