Selective suppression of alimentary tract microbial flora as prophylaxis during granulocytopenia.

Oral nonabsorbable antibiotics have been used to suppress the rectal flora in granulocytopenic patients. Problems with these therapies, i.e., compliance, acquisition of undesirable flora, and cost, motivated the search for an alternative therapy which would increase compliance and effectively reduce the Enterobacteriaceae without creating a microbiol vacuum. Trimethoprim-sulfamethoxazole was found to be easily taken, to suppress the Enterobacteriaceae, and to maintain the anaerobic rectal flora for biological stability of the rectal ecosystem. However, concurrent use of parenteral antibiotics profoundly influenced rectal flora and temporarily destroyed the colonization resistance afforded by the anaerobes.