The Effect of Adjunctive Systemic Antibiotics on the Outcomes of Non‐Surgical Periodontal Therapy: A Retrospective Cohort Study

ABSTRACT Aim To evaluate the real‐world comparative effectiveness of various adjunctive systemic antibiotic regimens in combination with scaling and root planing (SRP) using a large, multi‐centre retrospective cohort. Materials and Methods Electronic health records were used retrospectively to categorise periodontitis patients into ‘SRP Only’ or ‘SRP + Antibiotic’ groups based on prescriptions within 7 days of therapy. Primary outcomes included changes in probing depth (PD), clinical attachment level (CAL), percentage of sites with PD ≥ 4 mm and bleeding on probing (BOP). Secondary outcomes assessed tooth‐level worsening in mobility or furcation status. Results Among 3125 patients, the amoxicillin + metronidazole combination was found to be statistically superior to SRP alone for reducing PD, BOP and residual disease burden. It significantly reduced the odds of worsening tooth mobility by 63% and furcation involvement by 50%. While azithromycin and doxycycline improved CAL, the benefits of the amoxicillin + metronidazole combination were most pronounced in Stage III/IV (severe) periodontitis (−11.4% residual burden reduction, OR 4.55 for clinical success), compared to a modest effect in Stage I/II disease (−3.8%, p = 0.030). Conclusion Adjunctive systemic antibiotics, particularly the amoxicillin + metronidazole combination, significantly enhance clinical outcomes in non‐surgical periodontitis treatment compared to SRP alone, with the greatest benefits seen in severe disease.