BACTERIAL-RESISTANCE FOLLOWING SUBGINGIVAL AND SYSTEMIC ADMINISTRATION OF MINOCYCLINE

The aim of the present study was to compare total numbers of cultivabl e bacteria and prevalence of resistance to minocycline among periodont al bacteria following subgingival or systemic application of minocycli ne in patients suffering from periodontal disease. 10 adult patients w ere administered 2% minocycline ointment subgingivally into their peri odontal pockets at baseline, week 2 and months 1, 3, 6 and 9. Patients had scaling/root planing at baseline and month 6. In addition, 10 pat ients undergoing scaling/root planing followed by a 10-day course of s ystemic minocycline therapy, were studied and compared with the subgin gival application group. Bacterial samples were taken from the 4 deepe st pockets before each subgingival application of the drug. The system ic administration group was sampled at baseline and at week 2, as well as months 1 and 3 after completing the antibiotic treatment. For each patient at each sampling, bacterial samples were pooled, diluted, see ded on parallel blood agar plates and incubated aerobically and anaero bically. After incubation, 30 colonies were picked at random and trans ferred to blood agar plates supplemented with 10 mu g/ml minocycline, to estimate prevalence of minocycline-resistant bacteria. The results of this study indicate that subgingival application of minocycline oin tment resulted in an initial reduction in total numbers of cultivable bacteria, which then remained depressed during the full year of the st udy. No such observation was made in the systemic administration. Both in the subgingival and the systemic administration group, the % of cu ltivable aerobic and anaerobic minocycline-resistant bacterial strains increased transiently following administration of the drug, but retur ned to baseline levels within 3 months post-treatment. The median of c ultivable aerobic minocycline-resistant bacterial strains decreased or remained unchanged in both groups during the study periods. Thus, sub gingival application of minocycline seems no more likely than systemic administration of the drug to select for an increased proportion of r esistant organisms in the periodontal pockets.