In vitro activity: Doripenem is active against Aeromonas (MIC50, 0.03 mg/L), Bacillus spp. (MIC50, 0.03 mg/L) and all tested anaerobic species (MIC range, < or =0.015-4 mg/L), but is less active against S. maltophilia (MIC90,>32 mg/L) and Enterococcus faecium (MIC90,>32 mg/L) among the enterococcal species. Doripenem is the most active carbapenem (MIC90, 1 to 4 mg/mL) against penicillin-resistant streptococci. Doripenem is found to be highly active against oxacillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci (2705 and 297 isolates, respectively; MIC90s 0.06 mg/L), with a potency greater than that of other carbapenem antibiotics. Doripenem is among the most potent agents tested against Streptococcus pneumoniae, viridans group streptococci and beta-haemolytic streptococci (885, 140 and 397 isolates; MIC(90)s 0.5, 0.5 and 0.03 mg/L, respectively). Doripenem is also active against Citrobacter spp., Enterobacter spp. and Serratia spp. (MIC90s 0.06-0.25 mg/L), including ceftazidime-resistant isolates. Doripenem is slightly more potent (MIC50 2 mg/L) than ertapenem and imipenem (MIC50 4 mg/L), and has a potency similar to that of meropenem (MIC50 2 mg/L), against Burkholderia cepacia (20 isolates). Doripenem demonstrates in vitro activity similar to that of meropenem against gram-negative pathogens and to that of imipenem against gram-positive pathogens.

Cell Assay: Doripenem hydrate was potent against Staphylococcus aureus and Staphylococcus epidermidis with the same MIC90 value of 0.063 μg/ml. Doripenem hydrate was 2-4 times more active than other tested carbapenems against S. aureus. The activity of doripenem hydrate against S. pneumoniae was similar to that of imipenem but higher than that of other tested agents. Doripenem hydrate was potent against S. pneumonia with an activity similar to that of other tested carbapenems (MIC90, 0.5 μg/ml). Doripenem hydrate had an activity similar to that of cefpirome against S. pneumoniae and S. pyogenes. Doripenem hydrate was more active against Enterococcus faecalis than other tested agents except for imipenem.