Effect of imipenem/cilastatin on the colonic microflora.

The effect of imipenem/cilastatin on the colonic microflora was investigated in 10 patients receiving the drug for six to 11 days. Fecal specimens were cultured quantitatively for aerobic and anaerobic microorganisms before, during, and after therapy. Imipenem/cilastatin treatment was associated with minor changes in the colonic flora. A small decrease in the numbers of enterobacteria, enterococci, anaerobic cocci, and organisms of the Bacteroides fragilis group was observed. After treatment was discontinued, the microflora returned to normal in all patients, and no new colonization with imipenem-resistant bacteria was seen. No patient had Clostridium difficile or its cytotoxin in feces. No adverse gastrointestinal reactions were registered.