Background/aims: To examine subgingival microbiological changes in chronic periodontitis subjects receiving scaling and root planing (SRP) alone or with systemically administered azithromycin, metronidazole or a sub-antimicrobial dose of doxycycline.
Methods: Ninety-two periodontitis subjects were randomly assigned to receive SRP alone or combined with azithromycin, metronidazole or sub-antimicrobial dose doxycycline. Subgingival plaque samples taken at baseline, 2 weeks, and 3, 6, and 12 months were analyzed for 40 bacterial species using checkerboard DNA–DNA hybridization. Percentage of resistant species and percentage of sites harboring species resistant to the test antibiotics were determined at each time-point.
Results: All treatments reduced counts of red complex species at 12 months, although no significant differences were detected among treatment groups for most species at all time-points. Both antibiotics significantly reduced counts of red complex species by 2 weeks. Percentage of resistant isolates increased in plaque samples in all adjunctive treatment groups, peaking at the end of administration, but returned to pretreatment levels by 12 months.
Conclusion: The significant reduction of red and orange complex species at 2 weeks in the subjects receiving SRP plus azithromycin or metronidazole may have contributed to a better clinical response in these treatment groups. Therapy did not appear to create lasting changes in the percentage of resistant isolates or sites harboring resistant species.