Oral antibiotic prophylaxis in protected environment units: effect of nonabsorbable and absorbable antibiotics on the fecal flora.

Eight patients in protected environment units received by the oral route a solution of gentamicin and vancomycin which completely suppressed all 78 strains of bacteria originally present in their stools. However, when the solution was discontinued bacteria were cultured again from the stools of every patient. Twenty-nine of the 42 strains cultured at this time were also cultured from pretreatment specimens. Oral absorbable antibiotics were given to six of these patients, but they eliminated only 10 of the 32 strains cultured from their stools. Seven of the 16 strains which persisted became resistant to the oral absorbable antibiotic. To achieve maximum effect, oral nonabsorbable antibiotic regimens must be continued as long as the patient remains in a protected environment unit.