Quantitative study of the antibacterial effect of cefotaxime and ceftriaxone during experimental Escherichia coli K1 bacteremia in chickens

: In order to assess the in vivo antibacterial activity of two cephalosporins of third generation, cefotaxime and ceftriaxone, we used the model of experimental bacteremia in chickens we had developed for a few years. 93 chickens were inoculated with 10(7) E. coli K1 coming from a meningitis in a new-born baby. 19 chickens were used as a control group; 29 were given ceftriaxone (50 mg/kg); 28 cefotaxime (50 mg/kg) and 17 cefotaxime (100 mg/kg). The antibiotics were injected 4 hours after the inoculation. The bacterial concentrations found in capillaries by using quantitative blood cultures, were significantly lower in the 3 groups of chickens which were given antibiotics than in the control group, at 24, 48 and 72 hours after inoculation. At 24 hours after the inoculation, the bacterial concentration in the chickens treated by ceftriaxone (50 mg/kg) was significantly lower than that found in chickens treated by cefotaxime (50 mg/kg). At 48 or 72 hours the differences of bacterial concentration in the three groups of chickens were not significant. Over 72 hours following inoculation, 4 control and only one treated chickens died. The efficient clearance of E. coli K1 by a single dose of ceftriaxone, found at 24 hours after inoculation, confirms the possibility of using ceftriaxone once daily for serious infections.