Treatment options for extended-spectrum beta-lactamase-producers.

A review of antibiotic options for the treatment of infections caused by extended-spectrum beta-lactamase-producing isolates is presented. The use of the third-generation cephalosporin, cefotaxime, for infections caused by isolates producing ceftazidimase-type extended-spectrum beta-lactamases is controversial, despite in vitro susceptibility to the antibiotic in many instances. The fourth-generation cephalosporin, cefipime, although active against most extended-spectrum beta-lactamases, is reported to show a marked inoculum effect. The cephamycins, such as cefoxitin. are generally effective against Enterobacteriaceae producing TEM- and SHV-derived extended-spectrum beta-lactamases, but Klebsella pneumoniae strains are prone to cephamycin resistance as a result of porin loss. The use of beta-lactamase inhibitor combinations is variable. Sulbactam is less effective than clavulanate for the inhibition of SHV-derived extended-spectrum beta-lactamases and a marked inoculum effect has been noted, while the efficacy of tazobactam against SHV-derived extended-spectrum beta-lactamase producers is controversial. Furthermore, extended-spectrum beta-lactamases are often encoded by multi-resistant plasmids carrying genes conferring resistance to aminoglycosides, chloramphenicol, sulfonamides, trimethoprim and other antimicrobials, severely limiting even alternative therapies. Extensive susceptibility testing before the institution of antibiotic therapy is thus vital.