Antibiotics in Dentistry: Usage, Classification, and Mechanisms
Antibiotics in Dentistry
Antibiotics are naturally occurring, artificial, or microorganism-derived substances that can stop or destroy bacteria, fungi, and protozoa. Dr. Fleming discovered penicillin in 1929, marking the first antibiotic used. Initially, all antibiotics were natural. Later, semi-synthetic and synthetic antibiotics were developed by transforming original molecules to enhance pharmacological advantages.
Mechanisms of Action
Inhibition of cell wall synthesis enzymes (murein).
Alteration of plasma membrane permeability.
Inhibition of protein synthesis (tetracycline, aminoglycosides, macrolides).
Inhibition of nucleic acid metabolism.
Bactericidal vs. Bacteriostatic
Bactericidal antibiotics eliminate microorganisms without compromising the patient’s defenses.
Bacteriostatic antibiotics reversibly inhibit essential organism processes, requiring the patient’s defense system for bacterial destruction.
Conditions for Antibiotic Effectiveness
Activity against microorganisms.
Absorption by the body.
Activity in tissues and body fluids.
Low toxicity.
Minimal resistance development.
Antibiotic Spectrum and Antibiogram
The antibiotic spectrum encompasses all infectious agents susceptible to an antibiotic’s action.
An antibiogram is a test determining the antibiotics to which an organism is sensitive.
Microbial Resistance to Antibiotics
Microorganisms can develop resistance naturally (e.g., bacteria without walls are unaffected by murein synthesis inhibitors) or acquire it through gene mutations that alter the antibiotic’s target structure.
Factors Influencing Susceptibility and Resistance
Isolation of pathogenic bacteria.
Determination of bacterial sensitivity.
Antibiotic concentration at the infection site.
Classification by Chemical Nature
Beta-lactams: Penicillins (G and V), amoxicillin, cephalosporins, monobactams, carbapenems, beta-lactamase inhibitors (clavulanate, sulbactam). Mode of Action: Inhibit murein synthesis, causing bacterial lysis (death). Bacterial defense mechanisms include beta-lactamases, which hydrolyze the lactam ring, destroying penicillin activity. Resistance: Natural (organisms without walls), phenotypic (bacteria with defective walls), genotypic (changes in permeability, enzymatic hydrolysis, target enzyme changes).
Aminoglycosides (streptomycin, gentamicin): Bactericidal.
Tetracyclines: Bacteriostatic.
Phenicols (chloramphenicol): Bacteriostatic.
Macrolides (erythromycin, azithromycin, spiramycin): Bacteriostatic.
Lincosamides (clindamycin, lincomycin): Bacteriostatic.
Quinolones (norfloxacin): Bacteriostatic.
Sulfonamides: Bacteriostatic.
Imidazoles (metronidazole): Bacteriostatic.
Antibiotic Use in Dentistry
Antibiotic use must be tailored to each patient, considering infection severity, affected area, and etiologic agent. Antibiotics can be used for prophylaxis (preventing infection), empirically (targeting the suspected organism), or directed (when the organism is identified). Cultures and susceptibility tests help identify appropriate antibiotics. The chosen antibiotic should have high tissue distribution and reach high concentrations in oral tissues. Oral administration is preferred, with gastric protectors for patients with gastrointestinal issues.
Children: Dosage adjusted to body weight (tetracyclines avoided under 8 years).
Elderly: Lower doses for parenteral administration.
Pregnancy: Avoid sulfonamides (neonatal jaundice risk) and chloramphenicol. Beta-lactams or macrolides preferred.
First-Choice Antibiotics in Dentistry
Used for outpatient treatment of mild to moderate odontogenic infections.
Natural Penicillins: Beta-lactams with bactericidal activity, excellent distribution, low toxicity, and low cost. Penicillin G (sodium and potassium) has a rapid effect (1.2-2.4 million units/day), effective against Streptococcus and anaerobic spirochetes. Penicillin G procaine (intramuscular) has delayed absorption but increased allergy risk. Penicillin V is also used.
Aminopenicillins: Semi-synthetic with increased resistance. Ampicillin (oral for mild infections, intravenous for severe). Amoxicillin has better absorption, used for prophylaxis (3g before surgery, 1.5g 6 hours after).
Macrolides: Oral use. Erythromycin has good absorption but can cause gastrointestinal upset. Used for mild to moderate infections when penicillin is contraindicated. Spiramycin crosses the placental barrier and is sold with metronidazole. Clindamycin is an antagonist.
Second-Choice Antibiotics in Dentistry
Indicated when first-choice antibiotics fail.
Metronidazole: Antimicrobial activity against bacteria and parasites. Oral absorption (slowed by food). Well-distributed in oral tissues, can cause gastrointestinal upset. Effective against acute necrotizing ulcerative gingivitis (ANUG), used with spiramycin.