Mechanical periodontal therapy is usually sufficient to treat the majority of periodontal diseases. But, in the case of certain aggressive periodontitis, antimicrobial medication must be combined with conventional non-surgical therapy.
Reasons:
-Certain microorganisms attach to periodontal tissues and invade them.
-Certain microbes are hard to eliminate because of their location (hard-to-reach areas).
-Certain pathogens are resistant to mechanical periodontal therapy.
Choice of antibiotic:
It depends on the bacteria responsible and the extent of the infection. After determining the nature of the microorganism in question with a bacterial culture, an effective antibiotic is selected.
Methods of administration:

- Systemic administration
For some patients, systemic antibiotics may be prescribed to be taken orally, to help treat their periodontal disease.
Indications:
- Aggressive periodontitis.
- Nonresponse to the mechanical treatment.
- Patients with a history of endocarditis or prosthetic valve (prophylactic antibiotherapy is necessary).
- In case of suppuration, during the initial treatment.
2. Local administration
Definition:
It consists in the insertion of the syringe or water jet to disinfect the pockets using an antibiotic or nonsteroidal anti-inflammatory drug.

Objectives:
- Perturbation of the subgingival flora.
- Sanitization and oxygenation the pocket.
- Stabilization of the bone lysis.
- Prevention of reinfection.
Indications:
- As a complement to the mechanical treatment for pockets < 5mm.
- After drainage of a periodontal abscess.
- Disinfection of pocket before surgery.
- Interradicular lesion.