The impact of different antimicrobial agents on the normal gastrointestinal microflora of humans.

In the present study the impact on the gastrointestinal microflora of peroral administration of penicillin, bacampicillin, clindamycin, erythromycin, doxycycline, and tinidazole was investigated. The effects on the colonic flora of parenteral administration of ampicillin plus sulbactam, cefoxitin, clindamycin, and tinidazole also were studied. Pronounced changes were observed in the oropharyngeal and colonic microflora in patients receiving clindamycin, erythromycin, and tinidazole (intravenous), whereas moderate changes were seen in those patients receiving doxycycline, cefoxitin, and ampicillin plus sulbactam. Penicillin, bacampicillin, and tinidazole (peroral) produced only minor changes. In most patients with an altered microflora, colonization with new bacterial strains was found.