The effect of a single intravenous dose of cefotaxime on the faecal flora.

Cefotaxime had an immediate effect on the faecal flora, mainly involving a loss of gram-positive organisms, but also reducing the number of Escherichia coli, Bacteroides spp. and Clostridium spp. There was little effect on the total bacterial counts because of compensatory increases in other species. These changes appear to initiate a period of instability in the composition of the faecal flora lasting for at least 14 days after the administration of cefotaxime. Other third-generation cephalosporins showed a similar prolonged disturbance to the stability of the faecal flora, but there were minor differences from cefotaxime in the bacterial species initially affected.