Cefepime for AmpC Infections: Can It Spare Carbapenems?

Why does cefepime matter after the pandemic's resistance surge?

CDC's account of COVID-19 and antimicrobial resistance documents a major setback: hospital-onset resistant infections and associated deaths across seven pathogens each increased by at least 15% between 2019 and 2020. Staffing pressures, longer admissions, greater use of invasive devices and disrupted infection prevention contributed to the problem. These are historical surveillance findings, rather than a new October announcement or an estimate specifically about AmpC infections. They provide context for choosing antibiotics carefully. [CDC pandemic overview](https://www.cdc.gov/antimicrobial-resistance/data-research/threats/covid-19.html).

AmpC enzymes allow certain bacteria to break down several antibiotics. In organisms such as Enterobacter cloacae complex, increased enzyme production can undermine treatment even when an initial test suggests susceptibility to ceftriaxone. Cefepime is relatively stable against AmpC and has a low tendency to stimulate its production. Infectious Diseases Society of America guidance supports cefepime for selected susceptible infections involving bacteria at moderate risk of clinically significant AmpC production. This recommendation concerns bacterial infections; cefepime does not treat the virus that causes COVID-19. [IDSA treatment guidance](https://www.idsociety.org/practice-guideline/amr-guidance/).

How strong is the evidence comparing cefepime with carbapenems?

A University Hospital Basel study published in the European Journal of Clinical Microbiology & Infectious Diseases examined 270 episodes of bloodstream infection involving AmpC-producing Enterobacterales. Of these, 162 received carbapenems and 77 received cefepime; the remaining episodes received other antibiotics. After excluding bacteria with phenotypic evidence of additional extended-spectrum beta-lactamase production, the investigators found no statistically significant difference in in-hospital mortality or recurrent infection between the cefepime and carbapenem groups. [Herrmann and colleagues](https://pubmed.ncbi.nlm.nih.gov/37993680/).

The study was retrospective, and patients receiving carbapenems were more likely to require intensive care at admission. Differences in illness severity and prescribing decisions complicate the comparison. A failure to detect a difference also cannot prove equivalent effectiveness, particularly in a relatively small study. The findings support cefepime as an option for appropriately selected patients, especially those who are clinically stable, while leaving uncertainty about more complex cases. They do not establish a survival advantage for cefepime. [Study findings and limitations](https://pubmed.ncbi.nlm.nih.gov/37993680/).

What determines whether cefepime is appropriate and safe?

AmpC is only one resistance mechanism. Additional enzymes, including extended-spectrum beta-lactamases, can change the treatment decision. Laboratory susceptibility results must therefore be interpreted alongside the bacterial species and clinical circumstances. Some results indicate that effectiveness depends on an optimized dosing regimen. IDSA's recommendation is conditional on those details; it does not mean cefepime is suitable for every resistant infection. [IDSA guidance on AmpC infections](https://www.idsociety.org/practice-guideline/amr-guidance/).

Kidney function is particularly important because cefepime is substantially cleared through the kidneys. Its prescribing information requires dose adjustment when adult creatinine clearance is 60 mL/min or lower. Excess exposure can cause serious neurological effects, including confusion, impaired consciousness, muscle jerking and seizures. These reactions occur especially with unadjusted doses in renal impairment, although appropriate adjustment does not eliminate the risk. New neurological symptoms during treatment need prompt clinical assessment. Cefepime can also cause serious allergic reactions and antibiotic-associated diarrhea, so monitoring extends beyond whether the infection is improving. [Cefepime prescribing information](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d63d360a-15ec-44a4-b80d-b2a5cb5759eb).