Antimicrobial effects of the combination of ceftibuten and an orally absorbed penem SCH 29482.

Ceftibuten is a new beta-lactamase-stable 3-aminothiazolyl cephalosporin that lacks activity against staphylococci and group-B streptococci. We determined the effect of the combination of ceftibuten with SCH 29482, an orally absorbed penem. The combination of the two agents was additive for 25% or indifferent for 57% of the Gram-positive species, Haemophilus, and Moraxella tested with a mean fractional inhibitory concentration (FIC) index of 0.75. The combination of ceftibuten and SCH 29482 was also indifferent for Bacteroides fragilis and other Bacteroides species, all of which were inhibited by less than or equal to micrograms/ml of SCH 29482. Antagonism of the combination was found for 80% of Serratia marcescens and for 30% of Citrobacter freundii and Enterobacter cloacae. Overall, the combination of ceftibuten and SCH 29482 at concentrations that can be achieved in serum after ingestion of 400 and 50 micrograms/ml, respectively, provided antibacterial activity against most Gram-positive aerobic and anaerobic species that cause upper respiratory, intraabdominal, and urinary infections.