Influence of third-generation cephalosporins on aerobic intestinal flora

Excretion of an antibiotic in bile may result in high intra-intestinal concentrations and thus alteration in the faecal flora. We investigated the effects of cefoperazone (75% biliary excretion), ceftriaxone (45%) and cefotaxime (5%) on the aerobic faecal flora. Cefoperazone reduced numbers of normal Gram-negative bacilli and selected resistant Pseudomonas, Serratia and Klebsiella-Enterobacter. Ceftriaxone was similar. However, cefotaxime had little effect on the normal Gram-negative flora, and did not promote the emergence of resistant organisms.