Treating endodontic infections

Determining infection source and appropriate course of treatment

Endodontic infections are polymicrobial and are made up of predominantly anaerobic bacteria and some facultative bacteria. A tooth with an infected nonvital pulp is a reservoir of infection that is isolated from the patient’s immune response and will eventually produce a periradicular inflammatory response. When the microbes invade the periradicular tissues, abscess and cellulitis may develop. The severity of this infection is dependent on the pathogenicity of the microbes and the resistance of the host. This response may not only give rise to an immunopathogenic and protective response but may also be destructive to the surrounding tissues and contribute to the adverse signs and symptoms.

The spread of infection and the associated inflammatory response will continue until the source of infection is removed. Patient evaluation, diagnosis, and treatment of the source of infection are of utmost importance.

Endodontic treatment of infection

The objectives for endodontic treatment are removal of the microbes, their byproducts, and pulpal debris from the infected root canal system. This allows a favorable condition for periradicular healing. When a patient has signs and symptoms associated with a severe infection, the canals should be disinfected and the access opening should be sealed to prevent coronal leakage.

In the rare case that there is continual drainage, the access may be left open until the next day to allow the accumulated irritants and inflammatory mediators to decrease to a level that allows the patient to initiate healing. Leaving a tooth open for an extended period of time allows for gross contamination with no further benefit to the patient. When there is localized swelling, increasing in size or associated with cellulitis, an incision for drainage should be considered. Incision for drainage is important to remove purulent materials and other inflammatory mediators. Drainage improves circulation to the infected tissues and increases delivery of the antibiotic to the area. Patients requiring extra oral drainage or hospitalization should be referred to an oral surgeon.

When a patient develops signs and symptoms of a severe endodontic infection, adjunctive antibiotics may be considered (see Table 1).

Antibiotics are not indicated in an otherwise healthy patient for a small localized swelling without systemic signs or symptoms of an infection (see Table 2).

Since their discovery in 1928, antibiotics revolutionized health care treatment of bacterial infections. Because they are relatively harmless to the host, they can be used to treat infections including those of endodontic origin. Antibiotics, however, may have an adverse effect by altering the normal flora, producing allergic reactions, and interacting adversely with other drugs.

TABLE 1: Indications for Adjunctive Antibiotics
  • Fever > 100 degree F
  • Malaise
  • Lymphadenopathy
  • Trismus
  • Increased Swelling
  • Cellulitus
  • Osteomyelitis
  • Persistent Infection
TABLE 2: Indications Not Requiring Adjunctive Antibiotics

Pain without signs and symptoms of infection

  • Symptomatic irreversible pulpitis
  • Acute periradicular periodontiti

Teeth with necrotic pulps and a radiolucency

Teeth with a sinus tract (chronic periradicular abscess)

Localized fluctuant swelling

Unfortunately, the wide use of antibiotics has fostered the selection of resistant bacteria. Antibiotics alter the natural balance of normal flora by selecting organisms that are resistant. Resistant genes are transferred vertically to all daughter cells. In addition, resistant genes can be transferred horizontally to other strains of bacteria by transduction, transformation and conjugation.

Thus strains of bacteria never exposed to the antibiotic may acquire resistance without ever coming into contact with the antibiotic. The selection of resistant organisms is enabled when a low dose of antibiotic is administered, when they are taken for long periods of time, or through noncompliance by patients. The development of resistance by bacteria because of inappropriate prescriptions raises questions and concerns for health care workers.

Antibiotics are used in addition to appropriate treatment to aid the host defenses. Narrow-spectrum antibiotics should be the first choice because broad spectrum antibiotics produce more alterations in the normal GI tract and select for additional resistant organisms. Systemic administration of the appropriate dosage is usually for 5 to 7 days. Clinical signs and symptoms should diminish in 2 to 4 days after diagnosis and removal of the source of infection. Because endodontic infections are polymicrobial, and antibiotic selection is empirical based on the organisms usually involved in endodontic infections, no single antibiotic is likely effective against all the strains of infecting bacteria. However, it is likely that if an antibiotic is effective against several strains, it will disrupt the microbial ecosystem.

Antibiotic (% Bacterial Susceptibility) Usual Dosage Comments
Penicillin VK (85%) Loading dose of 1000 mg followed by 500 mg every 4-6 hrs for 5-7 days Drug of choice for endodontic infections because it is narrow spectrum, high susceptibility, low toxicity, and low cost.
Amoxicillin (91%) Loading dose of 1000 mg followed by 500 mg every 8 hrs for 5-7 days May be used for serious odontogenic infections. Has a longer half life and higher, more sustained serum levels. Broad spectrum may cause more GI disturbance and selection of resistant organisms.
Amoxicillin & Clavulanate, i.e., AugmentinTM (100%) Loading dose of 1000 mg followed by 500 mg every 8 hrs for 5-7 days May be used for serious infections. Highest susceptibility. Broad spectrum, increased GI disturbance and selection of resistant organisms.
Clindamycin (96%) Loading dose of 600 mg followed by 300 mg every 6-8 hrs for 5-7 days 2nd choice antibiotic if patient is allergic to Penicillin. Effective against facultative and anaerobic bacteria. Reaches a concentration in bone approximating that of plasma.
Metronidazole (45%) Loading dose of 1000 mg followed by 500 mg every 6 hrs for 5-7days Bactericidal to anaerobes but lacks activity against aerobes. Effective when used in combination with Penicillin or Clindamycin.
Erythromycin Not effective against anaerobic bacteria. Significant GI upset. No longer recommended for treatment of endodontic infections.
Clarithromycin & Azithromycin (89%) Clarithromycin – 500 mg loading dose followed by 250 mg every 12 hrs for 5-7 days; Azithromycin – 500 mg loading dose followed by 250 mg once a day for 5-7 days. Macrolides that have spectrum of activity against some anaerobes.
Cephalosporins Usually not indicated for endodontic infections. 1st generation cephalosporins do not have activity against anaerobes found in endodontic infections.
Doxycycline Occasionally may be indicated when other antibiotics are contraindicated. Many strains of bacteria have become resistant to the tetracyclines.
Ciprofloxacin Quinilone antibiotic that is not effective against anaerobic bacteria.


It is important that clinicians understand the nature of polymicrobial endodontic infections and realize the importance of removing the reservoir of infection by endodontic treatment or tooth extraction. The prescription of antibiotics should be considered adjunctive to the clinical treatment of the patient; antibiotics should not be substituted for root canal debridement and drainage of purulence from a periradicular swelling.

Scroll to Top