In-vitro activity of two new carbapenems FCE 22101 and CGP 31608 in comparison with imipenem.

The minimum inhibitory concentrations (MICs) of two new penems, CGP 31608 and FCE 22101 were evaluated against 993 aerobic Gram-positive and Gram-negative bacteria and compared with imipenem. FCE 22101 was usually two to eight-fold more active than CGP 31608 except for Pseudomonas aeruginosa against which FCE 22101 was inactive. Both new penems were less active than imipenem. MBCs were equal to 1-2 X MICs. The effects of inocula, cations and serum were minimal. The MICs and MBCs were higher at pH 8 than at pH 6 or 7. Synergy between the new penems and amikacin was detected in 30% of the strains studied. Antagonism occurred with some Gram-positive bacteria.