Evaluation of the in vitro activity of two fourth-generation cephalosporins against bacterial samples isolated from patients in several Brazilian Hospitals

Cefpirome and cefepime are two fourth-generation cephalosporins recently introduced in Brazil. They have a very similar range of in vitro antimicrobial activity, but some differences have been noticed. The goal of this study was to compare the in vitro activity of cefpirome and cefepime against bacterial samples isolated in Brazilian hospitals. We studied 931 samples taken from hospitalized patients between April and June, 1998. The minimum inhibitory concentration (MIC) was determined by the Etest method. The potency of cefpirome was similar to that of cefepime, except against enterococci and coagulase-negative staphylococci, where cefpirome proved 2-fold more potent. The MICs90 for cefepime were inferior to cefpirome in response to Klebsiella pneumoniae (MICs90, 24 and 96µg/mL, respectively), Pseudomonas aeruginosa (MICs90, 48 and 128µg/mL, respectively), and other Gram-negative organisms (MICs90, 64 and 256µg/mL, respectively). Despite the fact that cefpirome presented a slightly broader range of action against Gram-positive bacteria(90 percent sensitive vs. 78 percent sensitive to cefepime), and that cefepime presented an equally broad range against Gram-negative bacteria (74 percent sensitive vs. 65 percent sensitive to cefpirome), these differences were not considered clinically significant because the sensitivity differed in MIC by less than 2 dilutions. Only 16 (1.7 percent) of the 931 samples tested showed a significant difference in sensitivity. This study suggests that, except for Acinetobacter sp. and P. aeruginosa, laboratories may routinely test only cefpirome and apply the same category result to cefepime. Since category discrepancies are very rare and cefpirome is slightly less active than cefepime against Enterobacteriaceae, isolates susceptible to cefepime will certanly also be susceptible to cefpirome. To optimize the treatment of severely infected patients, especially where species such as Acinetobacter sp and P. aeruginosa are involved, we recommend that both cephalosporins be tested by using the same susceptibility test method to determine the MIC.