Looking Beyond: Expanding the Utility of Cefazolin as a Surrogate Marker

Abstract

For uncomplicated urinary tract infections caused by Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, CLSI recommends the use of cefazolin as a surrogate marker for the oral third-generation cephalosporins cefpodoxime and cefdinir. However, they do not comment on cefixime, which has emerged as an alternate treatment option, especially in the pediatric population. Our aim is to determine whether the susceptibility results of cefazolin can predict susceptibility results to cefixime. We included 39 urinary isolates of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolated from patients with uncomplicated urinary tract infections. On comparing cefazolin and cefixime susceptibilities, it was observed that there was a categorical agreement in 36/39 isolates (92.3%), with Major Errors (ME) seen in 3 isolates. There were no Very Major Errors (VME) or Minor Errors (mE). In all three occasions of discrepancies, the isolate was susceptible to cefixime but resistant to cefazolin. Thus, similar to the other third-generation oral cephalosporins, a susceptible cefazolin result indicates susceptibility to cefixime, but if the isolate is resistant to cefazolin, cefixime needs to be tested individually.