Effect of phenoxymethylpenicillin and clindamycin on the oral, throat and faecal microflora of man.

Phenoxymethylpenicillin in capsules was given orally in doses of 800 mg twice daily for 7 days to 10 subjects. Saliva, throat and faecal specimens were taken up to 29 days for cultivation of aerobic and anaerobic bacteria. No changes in the normal flora in saliva, throat or faeces were noticed during the observation period. Clindamycin was given orally in doses of 150 mg 4 times daily to 10 other subjects. No changes in the aerobic oral flora were observed, while a significant decrease in the number of anaerobic bacteria occurred. In 2 volunteers, overgrowth of clindamycin-resistant clostridia were seen from days 4--16 in one and from days 2--7 in the other. The throat flora showed changes similar to the oral flora. Pronounced changes in the aerobic and anaerobic faecal bacterial flora occurred. Thus among the aerobes enterococci proliferated and among the anaerobes significant decreases in the number of cocci and gram-negative rods were noticed. In 4 subjects, clindamycin-resistant clostridia increased 4log. One of them developed diarrhoea and harboured an unidentified toxin-producing clostridial strain rather similar to Clostridium difficile.