Efficacy of cefotaxime and latamoxef for Escherichia coli bacteremia and meningitis in newborn rats.

We have evaluated the efficacy of cefotaxime and latamoxef against a Kl Escherichia coli strain in vitro and in vivo. In vitro, the minimal inhibitory concentrations (MICs) were close to the minimal bactericidal concentrations (MBCs) for both antibiotics (less than or equal to 2 dilutions). However, with an inoculum of 10(7) CFU/ml, MIC and MBC were significantly greater than those with inocula of 10(3) and 10(5). In vivo study with an infant rat model of bacteremia and meningitis revealed that both cefotaxime and latamoxef penetrated well into the cerebrospinal fluid (CSF), both drugs were bactericidal in blood and CSF, both were effective in prevention of the development of meningitis in bacteremic animals, and the mortality rates were significantly less in the treated than in the control group (p less than 0.001). However, even with cefotaxime or latamoxef treatment, the mortality was significantly greater (p less than 0.001) in rats whose bacterial counts before therapy were greater than or equal to 10(6) CFU/ml of blood. These findings suggest that the effects of cefotaxime and latamoxef may be directly correlated with the size of the bacterial population exposed to these agents and that this variable may be an important factor to influence the therapeutic outcome.