Impact of antimicrobial agents on human intestinal microflora.

The most common and significant cause of disturbances in the normal intestinal microflora is the administration of antimicrobial agents. The microflora can be influenced by antimicrobial agents because of incomplete absorption of any orally administered antimicrobial agent, secretion of an antimicrobial agent in the bile, or secretion from the intestinal mucosa. In most cases, the influence is not beneficial to the patient because suppression of the indigenous microorganisms often permits potential pathogens to overgrow and cause septic conditions, stomatitis, diarrhea, or colitis. Antimicrobial agents that influence the normal microflora also promote the emergence of antimicrobial-resistant strains. During the last fifteen years, the impact of different antimicrobial agents on the human microflora has been studied by several investigators. In this article published data on the impact of beta-lactam antibiotics, macrolides, tetracyclines, nitroimidazoles, clindamycin and quinolones on the human intestinal microflora are reviewed.