Evaluation of cefazolin as a surrogate marker for cefpodoxime susceptibility for urinary tract isolates

Of the cephalosporins, cefpodoxime has the most published clinical data for the treatment of urinary tract infections. In 2014, the Clinical and Laboratory Standards Institute (CLSI) guidelines recommended that cefazolin should be used as the surrogate marker for cefpodoxime among urinary tract isolates, replacing cephalothin. This study attempted to determine how well cefazolin serves as the surrogate marker. Additionally, it investigated how cefuroxime compared with cefazolin as a surrogate marker. The MicroScan Walkaway Plus system was used to determine susceptibility for cefazolin and cefuroxime on consecutive urine cultures with a colony count of ≥ 50 000 organisms. Only Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis isolates were included, following CLSI guidelines. Simultaneously, an Etest for cefpodoxime was conducted. The cefpodoxime interpretation was compared with that of the other two agents, and the categorical agreement was calculated, defined as the percentage of identical susceptibility interpretations. Cefazolin (92 %) had a significantly higher categorical agreement than cefuroxime (85 %) among 284 isolates (P = 0.011). The major error rate was 4.4 % for cefazolin and 1.1 % for cefuroxime. The very major error rate was 64 % for cefazolin and 18 % for cefuroxime among the 11 cefpodoxime-resistant isolates. Cefazolin was a better predictor of cefpodoxime susceptibility than the previously recommended agent, cephalothin. However, cefuroxime had better major and very major error rates than cefazolin.