The use of adjunctive systemic antibiotics in the treatment of periodontal diseases has always been somewhat controversial. Opposition to the systematic use of these agents in periodontal therapy is based on several arguments, including:
1. Lack of superior outcome compared to conventional mechanical therapy
2. High rate of recolonization of the subgingival microbiota, potentially requiring several rounds of antibiotics to maintain the clinical gains obtained
3. Induction of bacterial resistance
Despite these concerns, different systemic antibiotics have been tested as adjuncts to mechanical debridement in the treatment of periodontal infections since the late 1970s with mixed results. Eventually, serendipitous scientific discoveries led to the development of a highly efficacious antimicrobial therapy to treat periodontal diseases, namely the combination of metronidazole and amoxicillin. In the past decade, several clinical trials have tested the adjunctive use of this combination of antimicrobial agents in the treatment of aggressive periodontitis and moderate to severe forms of chronic periodontitis. The data accumulated by these studies are overwhelmingly in favor of the use of adjunctive systemic antibiotics. In my presentation, I will review the clinical and microbiological effects of these adjunctive antimicrobials, the risks associated with their use and make recommendations regarding their proper utilization in periodontal anti-infective therapy.