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Antimicrobial drugs in dentistry · Pharmacology · INBDE Patient Cases

Antimicrobial Pharmacology INBDE Patient Cases

By Dr. Isaac Sun, DDS

9 ADA INBDE-format patient cases on antimicrobial pharmacology. Each case is a shared patient box (chief complaint, history, medications, allergies, exam) followed by linked multiple-choice questions with full distractor explanations. Practice the way the real exam is structured.

9 patient cases45 linked questionsADA INBDE formatFull distractor explanations

Nine ADA INBDE-format patient cases on antimicrobial pharmacology: amoxicillin-clavulanate for a spreading odontogenic infection (source control plus antibiotic adjunct), choosing an alternative for severe penicillin allergy (clindamycin for treatment with C. diff counseling vs azithromycin/doxycycline for IE prophylaxis per 2021 AHA), metronidazole with alcohol (disulfiram-like) and with warfarin (INR rise), doxycycline avoided in pregnancy and in children under eight (calcium chelation and tooth staining), C. difficile colitis after clindamycin and oral vancomycin/fidaxomicin first-line treatment, fluconazole for oral candidiasis raising the INR sharply through CYP3A4/2C9 inhibition, acyclovir/valacyclovir for HSV labialis started in the prodrome, amoxicillin 2 g oral 30-60 minutes before procedures for infective endocarditis prophylaxis, and macrolide QT prolongation and CYP3A4 inhibition complicating antibiotic choice in patients on antiarrhythmics and statins. Topics include beta-lactams, macrolides, clindamycin, tetracyclines, metronidazole, fluoroquinolones, azole antifungals, nystatin, acyclovir, and dental antibiotic stewardship.

Case Coverage Map
What each case is testing
Amoxicillin-clavulanate for a spreading odontogenic infection:
Source control plus antibiotic adjunct, amoxicillin first-line, clavulanate for beta-lactamase, metronidazole add-on for anaerobes, and short course tailored to response.
Penicillin allergy and choosing an alternative antibiotic:
Severe PCN allergy excludes cephalosporins routinely; clindamycin still acceptable for treatment with C. diff counseling; for IE prophylaxis use azithromycin/doxycycline.
Metronidazole, alcohol, and warfarin:
Disulfiram-like reaction with alcohol, INR rise via CYP inhibition and gut-flora effects, INR monitoring, and local hemostasis for any dental bleeding.
Doxycycline avoided in pregnancy and young children:
Calcium chelation and tooth/bone effects, amoxicillin first-line in pregnancy, and fluoroquinolone/sulfonamide cautions in pregnancy.
C. difficile colitis after clindamycin:
Antibiotic-associated colitis from gut-flora disruption, stop offending agent + medical referral, oral vancomycin or fidaxomicin first-line, and future antibiotic choices.
Fluconazole for oral candidiasis on warfarin:
Topical nystatin first for uncomplicated thrush, systemic fluconazole sharply raises INR via CYP3A4/2C9, statin rhabdomyolysis risk, and rinse-and-spit ICS prevention.
Acyclovir for HSV reactivation (herpes labialis):
Acyclovir mechanism (viral TK + DNA polymerase), early prodrome initiation, valacyclovir prodrug benefit, and topical antivirals' limited efficacy.
Amoxicillin 2 g for infective endocarditis prophylaxis:
2 g amox 30-60 min pre-procedure adult dose, specific cardiac conditions and procedures, and 2021 AHA PCN-allergic alternative (azithromycin/doxycycline; not clindamycin).
Macrolide QT and CYP3A4 interactions in dental prescribing:
Macrolide QT prolongation with antiarrhythmics, CYP3A4 inhibition raising statin levels, azithromycin lowest interaction, cephalosporin in non-severe PCN allergy.
Patient case: Amoxicillin-clavulanate for a spreading odontogenic infection
0 of 5 answered, 0 correct
Patient
Male, 40 years old
Chief Complaint
Facial swelling, fever, and difficulty swallowing four days after onset of a left mandibular molar pain.
Background and/or Patient History
  • Untreated decayed mandibular molar with worsening pain
  • Fever to 38.6°C, left submandibular swelling, mild trismus
  • Source control (extraction) planned plus systemic antibiotic
Allergies
NKDA
Medications
  • None notable
Current Findings
  • Spreading odontogenic infection with systemic signs
  • Indication for empiric oral antibiotic plus extraction
  1. Question 1
    Moderate
    The cornerstone of management is:
  2. Question 2
    Easy
    The first-line empiric oral antibiotic for most odontogenic infections in a non-allergic adult is:
  3. Question 3
    Moderate
    When the infection has spread or is failing amoxicillin alone, a common step-up is:
  4. Question 4
    Moderate
    Adding metronidazole to amoxicillin is most appropriate when:
  5. Question 5
    Moderate
    Antibiotic duration in dental infection is typically:

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Patient case: Penicillin allergy and choosing an alternative antibiotic
0 of 5 answered, 0 correct
Patient
Female, 35 years old
Chief Complaint
Severe periapical infection needing an antibiotic; reports anaphylaxis to penicillin as a child.
Background and/or Patient History
  • Documented anaphylaxis to penicillin as a child
  • Now needs an antibiotic for a periapical infection in addition to source control
  • Discussion of safe alternative
Allergies
Penicillin (anaphylaxis)
Medications
  • None notable
Current Findings
  • True severe penicillin allergy
  • Indication for non-beta-lactam alternative
  1. Question 1
    Moderate
    After severe (anaphylaxis, SJS) penicillin allergy, cephalosporins are:
  2. Question 2
    Moderate
    A reasonable oral alternative for an odontogenic infection in this patient is:
  3. Question 3
    Moderate
    Clindamycin's major adverse effect to counsel is:
  4. Question 4
    Hard
    For routine IE prophylaxis (not active infection) in this severely PCN-allergic adult, current 2021 AHA guidance favors:
  5. Question 5
    Moderate
    The teaching point is that the PCN allergy label changes:

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Patient case: Metronidazole, alcohol, and warfarin
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Patient
Male, 58 years old
Chief Complaint
Started metronidazole for an anaerobic odontogenic infection; takes warfarin and drinks moderately.
Background and/or Patient History
  • Atrial fibrillation on warfarin
  • Habitual moderate alcohol use
  • Just started metronidazole alongside amoxicillin
Allergies
NKDA
Medications
  • Warfarin
  • Metronidazole (recent)
Current Findings
  • Concurrent warfarin + alcohol + new metronidazole
  • Two important interactions to counsel
  1. Question 1
    Moderate
    Metronidazole plus alcohol can produce:
  2. Question 2
    Easy
    The patient should be counseled to:
  3. Question 3
    Hard
    Metronidazole's interaction with warfarin causes:
  4. Question 4
    Moderate
    The dental team should coordinate with the physician to:
  5. Question 5
    Easy
    The teaching point is that metronidazole has two high-yield interactions:

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Patient case: Doxycycline avoided in pregnancy and young children
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Patient
Female, 28 years old, pregnant
Chief Complaint
Mild periodontal infection during the second trimester; question about doxycycline.
Background and/or Patient History
  • Pregnancy at 24 weeks
  • Periodontal infection that could be treated with a tetracycline class drug
  • Discussion of safer alternatives
Allergies
NKDA
Medications
  • Prenatal vitamin
Current Findings
  • Pregnant patient with periodontal infection
  • Tetracycline contraindication in pregnancy
  1. Question 1
    Moderate
    Doxycycline is AVOIDED in pregnancy because tetracyclines:
  2. Question 2
    Moderate
    A safer first-line oral antibiotic for an odontogenic infection in pregnancy is:
  3. Question 3
    Hard
    Beyond tetracyclines, other antibiotics generally AVOIDED in pregnancy include:
  4. Question 4
    Moderate
    Tetracyclines are also avoided in children younger than:
  5. Question 5
    Easy
    The teaching point is that the medical history (pregnancy, age, allergies, medications) drives:

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Patient case: C. difficile colitis after clindamycin
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Patient
Female, 65 years old
Chief Complaint
Persistent watery diarrhea, abdominal cramps, and low-grade fever five days after starting clindamycin for a dental infection.
Background and/or Patient History
  • PCN-allergic; started oral clindamycin for an odontogenic infection
  • Now with watery diarrhea, cramps, and fever
  • Concern for C. difficile-associated colitis
Allergies
Penicillin
Medications
  • Clindamycin (recent)
Current Findings
  • Diarrhea, cramps, low-grade fever after clindamycin
  • Clinical concern for C. difficile colitis
  1. Question 1
    Moderate
    C. difficile colitis follows antibiotic disruption of gut flora and is classically associated with:
  2. Question 2
    Moderate
    Immediate dental and medical steps include:
  3. Question 3
    Hard
    First-line treatment for C. difficile colitis is currently:
  4. Question 4
    Moderate
    For the patient's next antibiotic course (if needed), the dentist should:
  5. Question 5
    Easy
    The teaching point is that clindamycin's adverse effect profile is dominated by:

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Patient case: Fluconazole for oral candidiasis on warfarin
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Patient
Male, 75 years old
Chief Complaint
Oral candidiasis from an inhaled corticosteroid; on warfarin for atrial fibrillation.
Background and/or Patient History
  • Inhaled corticosteroid for COPD; pseudomembranous candidiasis on examination
  • Warfarin for atrial fibrillation; INR stable in range
  • Considering fluconazole for systemic candida therapy
Allergies
NKDA
Medications
  • Warfarin
  • Inhaled budesonide
Current Findings
  • Oral candidiasis from ICS
  • Warfarin patient; CYP interaction concern with azole
  1. Question 1
    Moderate
    Mild ICS-related oral candidiasis is often treated with:
  2. Question 2
    Hard
    Systemic fluconazole interacts with warfarin to:
  3. Question 3
    Moderate
    If a systemic azole is necessary, the dental team should:
  4. Question 4
    Hard
    Azole antifungals also raise the levels of:
  5. Question 5
    Easy
    ICS-related candidiasis is also prevented by:

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Patient case: Acyclovir for HSV reactivation (herpes labialis)
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Patient
Male, 28 years old
Chief Complaint
Tingling on the lip with early vesicle formation; recurrent cold sores three times per year.
Background and/or Patient History
  • Recurrent herpes labialis with classic prodrome of tingling and burning
  • Current visit during prodrome
  • Considering antiviral therapy
Allergies
NKDA
Medications
  • None
Current Findings
  • Prodromal HSV-1 reactivation
  • Indication for early antiviral therapy
  1. Question 1
    Moderate
    Acyclovir treats HSV by:
  2. Question 2
    Moderate
    Early antiviral therapy works best when started:
  3. Question 3
    Moderate
    Valacyclovir is preferred over oral acyclovir for episodic herpes labialis because it:
  4. Question 4
    Moderate
    Topical antivirals (penciclovir cream, acyclovir cream) are:
  5. Question 5
    Easy
    The teaching point is that HSV reactivation:

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Patient case: Amoxicillin 2 g for infective endocarditis prophylaxis
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Patient
Female, 60 years old
Chief Complaint
Scheduled scaling and root planing in a patient with a prosthetic heart valve.
Background and/or Patient History
  • Prosthetic heart valve, a high-risk cardiac condition for IE
  • Scaling and root planing planned (a procedure that manipulates gingiva)
  • Discussion of antibiotic prophylaxis
Allergies
NKDA
Medications
  • Warfarin
  • Statin
Current Findings
  • Indication for IE prophylaxis
  • Drug-pharmacology focus on amoxicillin 2 g pre-procedure
  1. Question 1
    Moderate
    The standard adult IE prophylaxis regimen for a non-allergic patient is:
  2. Question 2
    Moderate
    Amoxicillin reaches an effective bloodstream level after oral dosing because:
  3. Question 3
    Moderate
    IE prophylaxis is indicated only for specific cardiac conditions, including:
  4. Question 4
    Moderate
    IE prophylaxis is required for dental procedures that:
  5. Question 5
    Hard
    For a severely penicillin-allergic adult needing IE prophylaxis, current 2021 AHA guidance recommends:

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Patient case: Macrolide QT and CYP3A4 interactions in dental prescribing
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Patient
Male, 70 years old
Chief Complaint
Antibiotic needed for an odontogenic infection; takes a QT-prolonging antiarrhythmic and a statin.
Background and/or Patient History
  • Atrial fibrillation managed with sotalol (QT-prolonging)
  • Atorvastatin for hyperlipidemia
  • Antibiotic decision for a dental infection
Allergies
Penicillin (mild rash as a child)
Medications
  • Sotalol
  • Atorvastatin
Current Findings
  • QT-prolonging drug already on board
  • Statin metabolized by CYP3A4
  • Antibiotic choice complicated by macrolide cautions
  1. Question 1
    Hard
    Macrolides (azithromycin, clarithromycin, erythromycin) raise concern in this patient because they:
  2. Question 2
    Moderate
    Among macrolides, the one with the LEAST CYP3A4 interaction is:
  3. Question 3
    Hard
    Given a documented but mild childhood PCN rash (not anaphylaxis), a reasonable approach is:
  4. Question 4
    Moderate
    If azithromycin is chosen, the clinician should:
  5. Question 5
    Easy
    The teaching point is that the medical history:

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