Correlation of cefpodoxime susceptibility with cephalothin and cefuroxime for urinary tract isolates

Abstract

This study attempted to determine whether cefuroxime was superior to cephalothin as a surrogate marker for cefpodoxime among urinary tract isolates. The MicroScan system (Siemens) was used to determine susceptibility for cephalothin and cefuroxime on consecutive cultures with a colony count of ¢50 000 organisms. Simultaneously, an Etest (bioMé rieux) for cefpodoxime was conducted. The cefpodoxime interpretation was compared to that of the other two agents, and the categorical agreement was calculated, defined as the percentage of identical susceptibility interpretations. Cefuroxime (83 %) had a significantly higher categorical agreement than cephalothin (63 %) among 300 isolates (P,0.01). The major error rate was 16 % for cephalothin and 3 % for cefuroxime. The very major error rate was 7 % for cephalothin and 14 % for cefuroxime among the 14 cefpodoxime-resistant isolates. For Escherichia coli, the major error rates were 15 % and 1 % for cephalothin and cefuroxime, respectively. Very major error rates were 9 % for both agents. Cefuroxime was a better predictor of cefpodoxime susceptibility than cephalothin, and appears to be the preferred surrogate agent for the MicroScan system, particularly for E. coli.

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

“…It performed much better than the previously recommended surrogate, cephalothin, which produced a categorical agreement rate of 63 % and a major error rate of 16 % in a prior study (Bookstaver et al, 2014;CLSI, 2013). However, major error and very major error rates for cefazolin were above the thresholds set by the FDA.…”

“…Cultures were excluded if they were positive for more than three organisms, as this was suggestive of contamination. Isolates from a previous study comparing cephalothin with cefuroxime were utilized (Bookstaver et al, 2014); however, only Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis isolates were included, following the CLSI guidelines (CLSI, 2015).…”

“…A sample size calculation prior to the initial study (Bookstaver et al, 2014) Cefazolin MIC (μg ml isolates were needed to assess whether the rates differed by more than 5 % with an a error of 0.05 and a power of 80 %.…”

“…However, they do include a caveat that isolates may test resistant to cefazolin but are actually sensitive to cefpodoxime. The purpose of this study was to determine how well cefazolin served as a surrogate marker for cefpodoxime, and how it compared with cefuroxime, which has been shown to be superior to the previously recommended surrogate marker, cephalothin (Bookstaver et al, 2014;CLSI, 2013).…”