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J Clin Periodontol. 2005 Nov;32(11):1163-9.

Long-term treatment with sub-antimicrobial dose doxycycline has no antibacterial effect on intestinal flora.

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Periodontal Disease Research Clinics, University of Florida, Gainesville, FL 32610, USA.



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.


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.


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.


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.

[Indexed for MEDLINE]

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