It is generally recognized that sub-minimum inhibitory concentrations (sub-MICs) of antibiotics are still capable of interfering with some bacterial virulence parameters, thus facilitating host neutrophilic defenses such as phagocytosis, killing and oxidative bursts. This study investigated the interaction of Escherichia coli with these neutrophilic functions after pretreatment with various sub-MICs of cefodizime. E. coli exposed to 1/2 to 1/8 MICs of cefodizime showed the extensive production of long and very long filaments that interfere with the precise measurement of phagocytic and killing parameters. Our analysis was consequently extended to the activity of 1/16 to 1/64 MICs. The interesting finding was that, although phagocytosis was unaffected, killing was significantly increased in one strain at 1/16 MIC and in another at 1/32 MIC while in the last strain it was unaffected. Oxidative bursts were not modified by any of the sub-MICs. The knowledge that these sub-MICs are still effective in increasing bacteria killing, correlated with the pharmacokinetic curve of a common single dose of cefodizime 1 g i.m., showed that the killing effects of sub-MICs may last for as long as 12 h after the activity of the MIC value. This integrated information extends our knowledge of the ultimate efficacy of an antibiotic and provides further information for optimizing scheduling.