Cidal activity of oral third-generation cephalosporins against Streptococcus pneumoniae in relation to cefotaxime intrinsic activity
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This study explores the killing kinetics within 12 h of four oral third-generation cephalosporins against ten Streptococcus pneumoniae strains exhibiting cefotaxime minimum inhibitory concentrations (MICs) from 0.03 to 2 μg/ml. Killing curves were performed with concentrations achievable in serum after standard doses (0.015–4 μg/ml). Reductions of 90% were achieved with all compounds at serum-achievable concentrations for strains exhibiting cefotaxime MIC≤0.5 μg/ml. Against strains with cefotaxime MIC≥1 μg/ml, only cefditoren reached a 90% reduction with concentrations of 0.5–1 μg/ml doses. At 4 μg/ml, cefditoren and cefotaxime reached 99.9% reduction in seven of the ten strains studied. At serum-achievable concentrations, cefdinir and cefixime were not bactericidal against strains exhibiting cefotaxime MIC≥0.25 μg/ml and ≥0.5 μg/ml, respectively. Cefditoren showed the best killing kinetic profiles and this observation may be important when choosing an oral third-generation cephalosporin as initial or sequential therapy.
KeywordsCeftriaxone Cefotaxime Cefixime Cefpodoxime Initial Inoculum
The authors thank A. Fenoll (Spanish Pneumococcal Reference Laboratory) for the supply of the strains used in this study, and for her critical review of the manuscript.
This study was supported by an unrestricted grant from GlaxoSmithKline S.A., Tres Cantos, Madrid, Spain.
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