Faecal Concentration of Ten Antibiotics and Influence on Some Microflora-Associated Characteristics (MACs)

Ten antimicrobial agents were given for 6 d to six or seven healthy volunteers. Ampicillin 500 mg q.i.d., bacitracin 25 000 1U q.i.d., clindamycin 150 mg q.i.d., co-trimoxazole 160/800 mg b.i.d., doxycycline 200 mg on day 1, followed by 100 mg daily, erythromycin 250 mg q.i.d., metronidazole 400 mg t.i.d., nalidixic acid 500 mg q.i.d., ofloxacin 200 mg b.i.d. or vancomycin 240 mg q.i.d. Faecal sampling was done before, during and after medication. Drug concentrations were measured in faxes and blood on day 6. All faecal samples were investigated for the presence of enteropathogenic microbes and for alterations of biochemical microflora associated characteristics (MACs): conversion of cholesterol to coprostanol, bilirubin deconjugation and formation of urobilinogen, 7α-dehydroxylation of bile acids, breakdown of mucin, presence of β-aspartylglycine, inactivation of tryptic activity and production of short chain fatty acids. Except ampicillin and metronidazole, antimicrobial activity was detected in faeces from all subjects. Intake of ampicillin induced production of β-lactamases in all but one subject. A toxin-producing strain of Clostridium difficile was found in one subject receiving clindamycin. Substances resulting in high faecal concentrations (i.e. clindamycin, bacitracin and vancomycin) resulted in the most profound alterations of the MACs studied. Such alterations in MACs may reflect severe disturbances in the intestinal ecosystem. Keywords: Ecology; intestinal microflora; Antimicrobial agents; Microflora associated characteristics; Faecal concentration of antibiotics.