Antibiotics for Oral Disease

Antibiotic Use

Antimicrobial agents have been extensively used (in both human and veterinary medicine) for more than half a century and the potential and limitations of this therapy are now better understood.

Problems, resulting from the widespread use of antibiotics, have modified the general perception of the capabilities of antimicrobial agents. Over the years, bacteria have developed a marked ability to withstand or repel many antibiotic agents. Bacteria are increasingly resistant to many formerly potent agents. The use of antibiotics may disturb the delicate ecologic equilibrium of the body, allowing the proliferation of resistant bacteria and/or nonbacterial organisms. Sometimes this may initiate new infections that are worse than the ones originally treated. In addition, no antibacterial drug is completely nontoxic and the use of any antimicrobial agent will have accompanying risks. It must also be remembered that resistant bacteria can cross the species barrier. Antibiotics and antiseptics have a role to play in the management of oral diseases, but their use should be limited and selective.

Dosing regimens and strategies that lead to optimal efficacy of antimicrobial agents must be implemented. Antibiotics can be used for prevention and for therapy.

Preventive Use of Antibiotics

The main objective of preventive (prophylactic) antibiotics is to prevent treatment-induced bacteremia. Periodontal therapy, tooth extraction and surgical treatment of oral trauma cause a considerable bacteremia, which typically clears in around 20 minutes. The preventive or prophylactic use of antibiotics should only be necessary in patients that cannot cope with the treatment-induced bacteremia.

Animals that should receive preventive antibiotic administration are:

• Geriatric or debilitated animals
• Patients with pre-existing heart and/or systemic diseases
• Immunocompromised patients.
  
  

In addition to preventing treatment-induced bacteremia, preventive antibiotic administration helps control wound infection. Consequently, animals that may benefit from receiving preventive antibiotic administration are those affected by:

• Gross infection
• Chronic stomatitis
  
  

The choice of prophylactic antibiotic and protocol remains controversial. A wide variety of microorganisms is found in the flora of the mouth and saliva. Antibiotic prophylaxis requires a drug with antimicrobial activity against Gram-positive and Gram-negative aerobes and anaerobes. The timing of administration of antibiotics is critical. It is generally accepted that antibiotics should be administered within 2 hours of the surgery and not continued for more than 4 hours after the procedure (Peterson, 1994; Callender, 1999). In addition, antibiotics must be given at a high enough dose to reach a tissue level four times higher than the MIC of the causative organisms. A number of studies have shown that ampicillin, amoxicillin-clavulanic acid, certain cephalosporins and clindamycin meet the above requirements in dogs, cats and humans (Callender, 1999; Johnson et al, 1997; Harvey et al, 1995a; Harvey et al, 1995b; Mueller et al, 1999). A standard protocol often used is 20 mg/kg i.v. of ampicillin prior to surgery (at the time of catheter placement for anesthesia). This dose is repeated after 6 hours if the catheter is still in place. Metronidazole is given intravenously in addition to ampicillin in the presence of severe infection to ensure a wider anaerobic spectrum.

Therapeutic Use of Antibiotics

The therapeutic use of antibiotics is indicated in patients with local and systemic signs of established infection, i.e. marked swelling, pus formation, fever, lymphadenopathy and an elevated white blood cell count. Clinical judgement is important in making the diagnosis of infection and deciding on antibiotic therapy. Antibiotic administration ‘just to be on the safe side’ is not prudent use of antimicrobials.

Principles for prudent use of therapeutic antibiotics:

1. The causative agent should be identified and the antibiotic sensitivity determined. In the oral cavity, the organisms involved have been well defined and are known to include a mixed flora of aerobic and anaerobic, Gram-positive and Gram-negative bacteria. Empirical antibiotic treatment based on previous susceptibility studies is, therefore, acceptable. Amoxicillin clavulanic acid and clindamycin, and to a lesser extent cephalosporins, provide broad antibacterial activity against oral infections in dogs and cats. Culture is indicated for infection not responding to the initial treatment, recurrent infection, postoperative wound infection and osteomyelitis.
2. The antibiotic with the narrowest antibacterial spectrum should be used. This will minimize the risk of development of resistant bacteria.
3. Combinations of antibiotics are discouraged. The exception to this rule is the combination of amoxicillin or cephalosporins with metronidazole in severe mixed infections in which anaerobes are believed to play a major role.
4. A bactericidal antibiotic is preferable to a bacteriostatic agent. A bactericidal antibiotic (amoxicillin, cephalosporins and metronidazole) is preferred over a bacteriostatic antibiotic (clindamycin), mainly because there is less reliance on host inflammatory and immune reactions. Other considerations include the toxicity of the antibiotic and the patient’s history of previous allergic reactions to a particular antibiotic.
5. The antibiotic of choice must be administered at the proper dose and correct time interval. Refer to a current compendium of data sheets for veterinary products for correct dosing and time interval. A seven-day course of antibiotics is generally recommended. Osteomyelitis generally requires a longer period of treatment. Suboptimal dosing and/or pulse therapy is not recommended.
6. The patient must be monitored for response to treatment and the potential development of adverse reactions. Re-evaluation of the diagnosis is required if there is no response to treatment. Culture and antibiogram may well be indicated. Minor adverse reactions, e.g. mild gastrointestinal side effects and inappetance, due to changes in the gut flora as a result of systemic treatment with amoxicillin and clindamycin, occasionally occur.

Summary

• Antibiotics should be employed rationally based on accepted principles of preventive or therapeutic use. Indiscriminate and inappropriate use should be avoided.
• Empirical drug choice based on published studies of the nature of oral infections is usual, with culture and sensitivity being reserved for problem cases.
• Antibiotics are not indicated in the treatment of gingivitis. Their role in periodontitis is doubtful and is definitely secondary to conservative periodontal therapy.