Systemic doxycycline administration in the treatment of periodontal infections - (I) - Effect on the subgingival microbiota

Systemic doxycycline is one of the more common antimicrobial agents used in the treatment of periodontal infections and yet little is known of its eff ect on subgingival plaque composition during and after its administration. The purpose of the present investigation was to evaluate changes in subging ival plaque composition during and after 14 days of doxycycline administrat ion. 20 subjects with adult periodontitis were randomly assigned to test (n =10) and control (n=10) groups. The subjects received full mouth clinical a ssessment of pocket depth, attachment level, BOP, gingival redness, suppura tion and plaque accumulation at baseline and 90 days. All subjects received full mouth SRP at baseline and, additionally, the test group received 100 mg doxycycline daily for 14 days. Subgingival plaque samples were taken fro m the mesial surface of up to 28 teeth in each subject at baseline and 90 d ays. In addition, plaque samples were taken from 2 randomly selected teeth at 3, 7 and 14 days during and after antibiotic administration. Control sub jects were sampled at the same time points. Counts of 40 subgingival specie s were determined using checkerboard DNA-DNA hybridization and fluorescent detection. Significance of differences between test and control groups was determined at each time point using the Mann Whitney test. Significance of changes over time within test and control groups was determined using the Q uade test. A modest but significant reduction in mean pocket depth from bas eline to 90 days occurred in both test and control groups. A significant de crease in the % of sites with gingival redness occurred in the test group. There were no significant differences in proportions between test and contr ol groups for 33 of the test species at any time point. Test subjects exhib ited lower proportions of 4 Actinomyces species and an increase in 3 Strept ococcus species during antibiotic administration. After cessation of doxycy cline, Actinomyces sp. increased while Streptococcus sp. returned to baseli ne proportions. The relationship between these 2 genera appeared to be reci procal; an increase in one was accompanied by a decrease in the other. Peri odontal pathogens including B. forsythus, P. gingivalis, T. denticola and A . actinomycetemcomitans were not significantly altered by oral administrati on of doxycycline using conventional therapeutic dosage.