Microbiological effects of amoxicillin plus metronidazole in the treatment of young patients with Stages III and IV periodontitis: A secondary analysis from a 1‐year double‐blinded placebo‐controlled randomized clinical trial

Background Despite the body of evidence supporting the clinical benefits of metronidazole (MTZ) and amoxicillin (AMX) in the treatment of young patients with periodontitis, the microbiological outcomes of this antibiotic protocol have been less explored. This study evaluated the microbiological effects of adjunctive MTZ+AMX in the treatment of young patients with periodontitis. Methods Subjects with periodontitis Stages III or IV and ≤30 years old were randomly allocated to receive scaling and root planing (SRP) with placebo (n = 15) or with MTZ (400 mg) and AMX (500 mg) three times a day for 14 days (n = 15). Nine subgingival biofilm samples per subject (three samples from each probing depth (PD) category: ≤3, 4–6, and ≥7 mm) were collected at baseline and 3‐, 6‐, and 12‐months post‐treatment and individually analyzed for 40 bacterial species by checkerboard DNA–DNA hybridization. Results Thirty subjects (15/group) with mean ages 27.6 ± 3.5 (control) and 26.8 ± 3.9 (test) were included. At 12 months post‐therapy, the antibiotic group harbored lower proportions of red complex (1.3%) than the placebo group (12.5%) (p