Periodontal pathogens frequently colonize oral mucosa, tongue dorsum, tonsils and other domains and may translocate from non-periodontal sites to periodontal crevices. Systemic antibiotic therapy is administered to reinforce mechanical periodontal treatment and support the host defense system in overcoming the infection by killing subgingival pathogens that remain after conventional mechanical periodontal therapy. Combination antibiotic therapy may help broaden the antimicrobial range of the therapeutic regimen beyond that attained by any single antibiotic.