SUSCEPTIBILITY PATTERNS OF SELECT GRAM-NEGATIVE ORGANISMS AFTER A FORMULARY SWITCH FROM CEFTAZIDIME TO CEFEPIME
Lori L Hamm, David F Volles, Robert G Sawyer, and Kevin C Hazen

OBJECTIVE: To document changes in susceptibility patterns of gram-negative organisms, including Pseudomonas aeruginosa, Enterobacter aerogenes, Acinetobacter calcoaceticus, and Serratia marcescens after a formulary switch from ceftazidime to cefepime.

DESIGN, SETTING: Retrospective, observational study in a tertiary care, university teaching hospital.

PARTICIPANTS: Adult surgical patients with culture and susceptibility data.

MAIN OUTCOME MEASURES: Percent susceptible and median minimum inhibitory concentration values were evaluated for select gram-negative organisms from culture and susceptibility results. The time periods of one year before and two years after the formulary change were evaluated. Duplicate isolates were excluded. Different culture sites of infection were assessed for P. aeruginosa, including blood, urine, and lung.

RESULTS: A total of 957 samples from 489 patients were included. Susceptibility results after the formulary switch favored ceftazidime over cefepime for P. aeruginosa (79% vs. 54%; n = 485) and A. calcoaceticus (65% vs. 29%; n = 140). However, cefepime demonstrated greater kill rate with E. aerogenes isolates compared with ceftazidime (95% vs. 69%; n = 208). Susceptibility results were comparable with S. marcescens (100% for cefepime vs. 98% for ceftazidime). P. aeruginosa results from isolates taken from different culture sites did not differ from the overall results, as susceptibility was higher for ceftazidime compared with cefepime for all culture sites.

CONCLUSIONS: Susceptibility to cefepime and ceftazidime is organism-specific; therefore, it may be appropriate to include both agents on the formulary and/or implement an antibiotic rotation policy.

J Pharm Technol 2001;17:147-50.