In vitro antibacterial activities of different ratios from matching cefuroxime/tazobactam against clinical isolates

Objective To study the in vitro activity of cefuroxime alone and cefuroxime/tazobactam combined at various ratios (1∶1,2∶1,4∶1, 8∶1 )against clinical isolates.Methods Minimal inhibitory concentration(MIC) were determined by the twofold agar dilution and minimal bactericidal concentration (MBC) were determined by the twofold broth dilution method. Bactericidal curve was draw.Results MIC of cefuroxime/tazobactam against 661 clinical isolates (with 72.01%β-lactam producing) of 22 strains, which were isolated from 15 hospitals in 10 different areas in China between January 2001and January 2003,were measured.The in vitro activity against gram-negative bacilli was significantly enhanced by combined use of cefuroxime/tazobactam,especially to Escherichia coli,Klebsiella spp. ,Proteus spp., Morganella morganii , Enterobacter cloacae, and Citrobacter freundii.The inducing of tazobactam has significantly enhanced the antibacterial activities of cefuroxime,which the MIC_ 90 decreased to 1/8~1/30 of the original level,drug resistance rate reduced 12%~80%.The combination use of cefuroxime/tazobactam showed excellent anti-bacilli activity except to methicilline recietant Staphylococcus aureus and showed excellent bactericidal activity. MIC was unaffected by inoculum size and there was little variations affected by the concentration of human serum. The activity of cefuroxime/tazobactam against Escherichia coli and Klebsiella pneumoniae increased in alkalescence condition and decreased in the acidic environment. The best anti-bacterial activity of cefuroxime/tazobactam was achieved in the ratio of 1∶1 .Conclusion The combination of cefuroxime/tazobactam (1∶1) is an excellent bactericidal medicine.