[Synergism or antagonism in combinations of beta-lactam antibiotics]

Several examples of antagonistic combinations between cefoxitin and other beta-lactam antibiotics have been reported in the literature. This phenomenon may occur especially with Enterobacter spp, Pseudomonas aeruginosa, Citrobacter spp, and Serratia marcescens. In these species, induction of chromosomally mediated beta-lactamases by certain potent inducers, such as cefoxitin, has been suggested as the main mechanism of antagonism. These in vitro interactions may have clinical relevance; however, although studies in animal models have shown a few examples of in vivo antagonism, the actual clinical significance of interactions between beta-lactam antibiotics requires further thorough and controlled clinical studies.