Effect of broad-spectrum cephalosporins on the microbial flora of recipients.

The flora in the throat and the stools of 10 patients receiving chemotherapy for malignant diseases in a laminar air-flow room was studied during the prophylactic administration of ceftazidime. Ten percent of aerobic gram-negative bacilli, 41% of aerobic gram-positive organisms, 59% of anaerobes, and 70% of fungi persisted in stool specimens during ceftazidime administration. This drug had a less pronounced effect on the throat flora; 66% of organisms persisted during antibiotic administration. The throat and fecal flora of another eight patients were studied during the prophylactic administration of ceftriaxone. This antibiotic had a profound effect on the fecal flora; none of the gram-negative bacilli, only 24% of aerobic gram-positive organisms, and only 10% of anaerobes persisted during ceftriaxone administration. Like ceftazidime, ceftriaxone had a less marked effect on the throat flora; 59% of organisms persisted during antibiotic administration. The results show that new, expanded-spectrum cephalosporins can have a major suppressive effect on patients' endogenous microbial flora.