What is your approach to antibiotic selection for bacterial species that demonstrate susceptibility to penicillins or cephalosporins on testing, but are known to harbor inducible AmpC resistance?

I follow the recommendations from the IDSA guidelines (Tamma et al., PMID 39108079). Duration of treatment does not influence my decision about whether to use a beta-lactam for organisms with inducible AmpC. For Enterobacter cloacae complex, Klebsiella aerogenes, and Citrobacter freundii, I do not use a 1st to 3rd gen cephalosporin or PCN.

I will assess how long I am treating the person/infection, and go from there in terms of how likely I am to induce the AmpC based on the duration of treatment. For example, if it's a 7-day course for UTI or GN bacteremia, I may risk the penicillin/cephalosporin (based on susceptibilities, of course). If it's an osteomyelitis or other complex infection, using the 4-6 weeks of antibiotics, I would definitely consider other antimicrobials. One of my other considerations is how likely they are to have additional infections--i.e., recurrent UTIs, where I am also worried that this organism will be back. I also take into consideration which of the AmpC organisms it is and how likely I am to induce (e.g., Enterobacter, Citrobacter).

For what it's w...