High Yield Antibiotics to Know for the INBDE

Antibiotics are an important topic to know as they are constantly prescribed and used in “day to day” dentistry. After the High-Yield decision trees, below is a list of our high yield antibiotics to review and study for the INBDE!

Odontogenic Infections

One of the main indications for prescribing antibiotics in dentistry is for odontogenic infections. These infections typically start as carious lesions and progress outside of the tooth into the surrounding tissues. 

It is important to understand that the first line of treatment for odontogenic infections is always conservative dental treatment (i.e. fillings, root canal, incision and drainage) and to only prescribe antibiotics in the case of significant swelling and signs of systemic involvement. Below is a chart to help navigate when and what to prescribe in these situations.

Antibiotic Prophylaxis 

Another main indication of antibiotics in dentistry is to provide prophylaxis for infection in certain conditions. Here is a table of conditions that do and do not require antibiotic prophylaxis according to the American Dental Association (ADA).

In terms of what specific regimen is recommended for antibiotic prophylaxis, below is a decision tree on what antibiotics to prescribe based on the given situation. 

There are a few important things to note when going through the chart:

        1. Cephalexin/Cefazolin (1st generation) and ceftriaxone (3rd generation) are cephalosporins, which do have cross-reactivity to penicillin.

• However, the rate is so low in these specific forms that it is generally deemed safe to use as an alternative to penicillin.

        2. Clindamycin was previously recommended and still is commonly used for patients with penicillin allergies.

• Therefore, it is still an acceptable answer choice on the INBDE if azithromycin isn’t given as an answer choice

        3. Azithromycin is a very commonly used replacement for amoxicillin in an allergy situation.

Uses for Antibiotics in Dentistry

Before we get into the specific antibiotics, it is important to mention why antibiotics are even used in dentistry.

1. Treatment of infections: this includes abscesses and facial swellings
2. Post operative management: this includes a variety of endodontic or surgical procedures
3. Prophylaxis: this is for patients with specific conditions that need extra protection before dental treatment (more will be discussed below)

Bactericidal Antibiotics 

Antibiotics can either be “bactericidal” or “bacteriostatic.” Bactericidal agents function to kill the bacteria and are listed below.

Nitroimidazoles (i.e. Metronidazole, Tinidazole, Dimetridazole)

Suffix: 

• -dazole

Mechanism of Action:

• Damages microbial DNA and inhibits nucleic acid synthesis via reactive oxygen species

Indications: 

• Metronidazole is commonly prescribed in dentistry as a second line treatment that complements another antibiotic such as amoxicillin.  

Dosing/Route: 

• Can come in various IV or tablet formations
• For dentistry uses, metronidazole is commonly prescribed and is given 500mg TID for 7 days. 

Penicillins (i.e. Amoxicillin, Ampicillin, Methicillin)

Suffix: 

• -cillin

Mechanism of Action: 

• Binds β-lactam ring and inhibits cell wall synthesis  

Indications: 

• Amoxicillin, ampicillin and penicillin are the most commonly used antibiotics for dental concerns. 
• For dentistry uses, amoxicillin is most commonly prescribed and is usually given 500mg TID for 3-7 days

Dosing/Route: 

• There are many uses for the various penicillins, which can come in IV and oral tablet forms. Here are some of the highlights below:

• Penicillin G - IV form 
• Penicillin V - oral form

Other High Yield Facts:

• Penicillin is cross-allergenic with cephalosporins, which is another β-lactam antibiotic, due to their similar chemical structure

• This is a commonly tested board question!

Cephalosporins (i.e. Cefazolin, Cephalexin, Ceftriaxone, Cefixime)

Prefix: 

• Cef- or Cep-

Mechanism of Action: 

• Contains a beta-lactam ring that disrupts cell wall synthesis

Indications: 

• Also commonly prescribed in dentistry as an alternative to penicillin.

Dosing/Route: 

• Can come in various IV or tablet formations
• For dentistry uses, cephalexin or cefazolin is commonly prescribed and is given 500mg BID or TID for 7 days

Other High Yield Facts:

• Penicillin is cross-allergenic with cephalosporins

• However, the rate is so low in specific forms of cephalosporins that it is generally deemed safe to use as an alternative to penicillin

Bacteriostatic Antibiotics

Bacteriostatic agents prevent the growth of bacteria without killing them. Examples are listed below.

Tetracyclines (i.e. Tetracycline, Doxycycline, Minocycline)

Suffix: 

• -cycline

Mechanism of Action:

• Inhibits protein synthesis (30s ribosomal subunit) 

Indications:

• Used as an adjunct in periodontal therapy 

• Concentrates well in the gingival crevicular fluid
• Inhibits matrix metalloproteinases (MMPs) and helps prevents breakdown of collagen in gingival tissues

Dosing/Route: 

• Comes in tablet form
• For dentistry uses, doxycycline (periostat) is given 20mg BID for 3 months. 

Macrolides (i.e. Erythromycin, Clarithromycin, Azithromycin)

Suffix: 

• -thromycin

• Commonly confused with lincosamides (-mycin)
• Think “Mac (macrolides) likes to throw mice (-thromycin)”

Mechanism of Action: 

• Protein synthesis inhibitor (50s ribosomal subunit)

Indications: 

• Commonly used in dentistry as an alternative to penicillin

Dosing/Route:

• Comes in tablet form
• For dentistry uses, azithromycin is given at 500mg OID for 3 days

Lincosamides (i.e. Clindamycin, Lincomycin)

Suffix: 

• -mycin

• Commonly confused with macrolides (-thromycin)
• Think “Link (lincosamides) also hides mice (-mycin)”

Mechanism of Action: 

• Protein synthesis inhibitor (50s ribosomal subunit)

Indications: 

• Commonly used in dentistry as an alternative to penicillin

Dosing/Route:

• Comes in IV and tablet forms
• For dentistry uses, clindamycin is given 300 mg TID for 7-10 days

‍Drug/Drug interactions with Antibiotics

Although there are countless drug-drug interactions with the various antibiotics, here are a few high yield interactions that may show up on your exam!

1.  Bactericidal and Bacteriostatic drugs

• Fast growing bacteria are in their most vulnerable state to bactericidal drugs
• Bacteriostatic drugs function to slow the growth of bacteria and would actually be counterproductive when used with a bactericidal drug

2. Tetracyclines and Antacids

• Antacids or any dairy product reduces the effectiveness of tetracycline
• This is because tetracycline will bind to the calcium ions in antacids or dairy and will therefore not be absorbed in the body

3. Broad spectrum antibiotics and coumadin

• Many different antibiotics disrupt intestinal bacteria that produce vitamin K
• Coumadin is an anticoagulant that reduces the synthesis of vitamin K dependent clotting factors
• Therefore, these broad spectrum antibiotics would enhance the effect of coumadin

‍

Sources:

• Periostat dosage: https://www.medicines.org.uk/emc/product/90/smpc#gref‍
• Azithromycin dosage: https://pubmed.ncbi.nlm.nih.gov/12572095/‍
• Clinda dosage: https://www.khealth.com/learn/dental-infection/clindamycin
• Keflex dosage: https://www.rxlist.com/keflex-drug.htm