Impact of orally administered antimicrobial agents on human oropharyngeal and colonic microflora.

Phenoxymethylpenicillin, bacampicillin, clindamycin, erythromycin and doxycycline were given orally to 46 subjects for seven days. The numbers of aerobic and anaerobic bacteria in the oropharyngeal and colonic microflora were determined as were the concentrations of antimicrobial agents in saliva and faeces. Clindamycin, erythromycin and doxycycline were detected both in saliva and faeces. Phenoxymethylpenicillin, bacampicillin and doxycycline caused only minor changes in the microflora, while pronounced suppression of anaerobic bacteria was noticed when clindamycin was administered. Erythromycin decreased the aerobic bacteria in the oropharynx and both aerobic and anaerobic bacteria in the colon. New colonizing clostridia, enterobacteria and fungi were found both in the oropharynx and in the colon when erythromycin and clindamycin were administered.