title: Long-term treatment with sub-antimicrobial dose doxycycline has no antibacterial effect on intestinal flora.
abstract: OBJECTIVE
  The purpose of this study was to determine if a 9-month regimen of sub-antimicrobial doxycycline (20 mg, bid) had an effect on either the intestinal or the vaginal microflora.
  
  
  METHODS
  A total of 69 periodontally diseased subjects were randomized to receive drug or placebo control for a 9-month period. Stool specimens and vaginal swabs were collected at baseline and after 3 and 9 months of therapy. Samples were examined for total anaerobic counts, opportunistic pathogens, and doxycycline-resistant (>or=4 microg/ml) bacteria. All isolates that survived sub-culture were identified and their susceptibilities determined to six antibiotics. Analyses were performed to determine if treatment differences were present.
  
  
  RESULTS
  The only statistically significant differences (p<0.05) between the two treatment groups occurred in the doxycycline-resistant counts at the baseline sample period for the faecal samples. This imbalance was before treatment initiation and the administration of the study drug. No between-treatment differences were detected at either the 3- or 9-month sample period either in the predominant bacterial taxa present or in their antibiotic susceptibilities.
  
  
  CONCLUSIONS
  There was no evidence that sub-antimicrobial doxycycline treatment exerted an effect on the composition or doxycycline resistance level of either the faecal or the vaginal microflora.
authors.affiliation: Periodontal Disease Research Clinics, University of Florida, Gainesville, FL 32610, USA. walkerc1@ufl.edu
authors.forename: Clay
authors.initials: C
authors.lastname: Walker
authors.forename: Philip M
authors.initials: PM
authors.lastname: Preshaw
authors.forename: John
authors.initials: J
authors.lastname: Novak
authors.forename: Arthur F
authors.initials: AF
authors.lastname: Hefti
authors.forename: Mark
authors.initials: M
authors.lastname: Bradshaw
authors.forename: Christopher
authors.initials: C
authors.lastname: Powala
mesh_terms: D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology*; D004318:Doxycycline / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007422:Intestines / Q000382:microbiology*; D008137:Longitudinal Studies; D008875:Middle Aged; D010518:Periodontitis / Q000188:drug therapy*; D018709:Statistics, Nonparametric; D014621:Vagina / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D004318:Doxycycline