Effect of adjunctive systemic antibiotics on microbial populations compared with scaling and root planing alone for the treatment of periodontitis: A pilot randomized clinical trial.

Background: To investigate the microbial shift after periodontitis being treated by scaling and root planing (SRP) with or without adjunctive antibiotics, and to assess the relationship between oral microbiota and systemic factors.

Methods: A 6-month pilot randomized controlled trial recruited 14 subjects with severe periodontitis, divided into test group and control group to receive full-mouth SRP with or without amoxicillin (500 mg) and metronidazole (200 mg) (three times a day for 7 days). Clinical examination, collection of subgingival plaque and saliva, and blood tests were performed at baseline pre-treatment, 3 months, and 6 months post-treatment. The V3V4 region of 16S DNA was sequenced; taxonomic assignment was based on the Human Oral Microbiome Database.

Results: The periodontal condition significantly improved in both groups; the test group showed a greater improvement in plaque index, probing depth, and bleeding index than the control group. The test group demonstrated significantly lower microbial richness and diversity, and less abundant Porphyromonas than the control group at 3 months for both subgingival microbiome and salivary microbiome. However, the microbial differences narrowed within 6 months. The subgingival and salivary microbiota shifted synergistically. Glucose was positively related to subgingival Porphyromonas; mean platelet volume was positively related to subgingival Leptotrichia.

Conclusions: Systemic administration of amoxicillin and metronidazole along with SRP had an advantage over SRP alone in clinical improvement and infection control in both the subgingival region and saliva 3 months post-treatment. Microbial advantage nearly disappeared at 6 months; however, the clinical advantage lasted longer. The use of antibiotics also has potential benefits for systemic inflammation and glucose.