Changes in the oropharyngeal and colon microflora in relation to antimicrobial concentrations in saliva and faeces

Phenoxymethylpenicillin, bacampicillin, clindamycin, erythromycin, doxycycline and tinidazole were given perorally for 7 days to a total of 56 subjects. Concentrations of antimicrobials in serum, saliva and faeces were determined daily, as were viable counts of different aerobic and anaerobic microorganisms in the oropharyngeal and colon microflora. Clindamycin, erythromycin, doxycycline and tinidazole were detected in saliva. Clindamycin, erythromycin and doxycycline were also detected in high concentrations in faeces. Phenoxymethylpenicillin, bacampicillin, tinidazole and doxycycline did only induce small changes in the oropharyngeal and colon microflora, while distinct suppression of anaerobic bacteria was observed in the oropharynx and colon when clindamycin was administered. Erythromycin decreased the numbers of aerobic bacteria in oropharynx and both aerobic and anaerobic bacteria in colon. Both clindamycin and erythromycin induced new colonization of the oropharynx and colon by potentially pathogenic Gram-negative enteric rods and fungi as well as toxin-producing clostridia.