Adjunctive Hainosankyuto in Patients with Periodontal Abscess or Acute Exacerbation of Periodontitis Receiving Amoxicillin: Protocol for an Exploratory Randomized Controlled Trial

Background: Whether Hainosankyuto improves clinical outcomes when added to amoxicillin for acute periodontal infection is unknown. Methods: This investigator-initiated, single-center, exploratory, assessor-blinded, parallel-group randomized controlled trial will enroll 30 adults diagnosed with periodontal abscess or acute exacerbation of periodontitis for whom the treating dentist determines systemic amoxicillin is indicated. Participants will be randomized 1:1 to the protocol-defined amoxicillin regimen alone or with oral Hainosankyuto for 14 days and followed through Day 60. The six registered primary outcomes are dentist-assessed local inflammatory findings, OHIP-14 scores, probing depth, clinical attachment level, bleeding on probing, and scaling and root planing information. Secondary outcomes include serum IL-6, C-reactive protein, white blood cell count, potassium, and subgingival Porphyromonas gingivalis. Safety will be monitored throughout. Discussion: This exploratory trial will estimate preliminary effects of adjunctive Hainosankyuto within the registered regimen. Clinical findings and systemic biomarkers will not be interpreted as direct evidence of active resolution biology or histologic tissue repair. Trial registration: This study was prospectively registered in the Japan Registry of Clinical Trials (jRCTs071260057) on 21 July 2026.