1
COMSAE PHASE 1 FORM 112 PRACTICE EXAM — 176
QUESTIONS WITH FULL ROTATION RATIONALES
SECTION 1: MICROBIOLOGY & PHARMACOLOGY (Q1–40)
1. A 20-year-old college student presents with a sore throat, fever, and posterior
cervical lymphadenopathy. Examination reveals exudative tonsillitis and
splenomegaly. A complete blood count shows lymphocytosis with atypical
lymphocytes. Which of the following medications should be avoided due to risk
of a severe rash?
A) Penicillin V
B) Amoxicillin
C) Azithromycin
D) Clindamycin
E) Cephalexin
: Correct Answer : B
Full Rotation & Rationale:
• A (Penicillin V): Penicillin V is the treatment of choice for confirmed group
A streptococcal pharyngitis and does not commonly cause a rash in EBV
infection. However, the classic drug associated with a morbilliform rash in
EBV is ampicillin/amoxicillin.
• B (Amoxicillin): Correct. In patients with Epstein-Barr virus (infectious
mononucleosis), administration of amoxicillin (or ampicillin) causes a
characteristic, non-allergic maculopapular rash in up to 90% of cases. This is
not a true allergy but a Type IV hypersensitivity. Therefore, amoxicillin
should be avoided.
• C (Azithromycin): Macrolide; not associated with EBV-induced rash.
• D (Clindamycin): Lincosamide; not associated with EBV rash but carries risk
of C. difficile colitis.
pg. 1
,2
• E (Cephalexin): First-generation cephalosporin; may have cross-reactivity in
penicillin-allergic patients but does not cause the classic EBV rash.
2. A 65-year-old man with COPD is hospitalized with fever, productive cough,
and a right lower lobe infiltrate. Gram stain shows numerous neutrophils and
lancet-shaped gram-positive diplococci. He has a history of anaphylaxis after
amoxicillin. Which antibiotic is contraindicated?
A) Levofloxacin
B) Vancomycin
C) Cefazolin
D) Doxycycline
E) Azithromycin
: Correct Answer : C
Full Rotation & Rationale:
• A (Levofloxacin): Fluoroquinolone; safe in penicillin allergy.
• B (Vancomycin): Glycopeptide; no beta-lactam cross-reactivity.
• C (Cefazolin): Correct. Cephalosporins share a beta-lactam ring with
penicillins; cross-reactivity occurs in ~1-10% of penicillin-allergic patients.
With anaphylaxis to amoxicillin, cephalosporins are contraindicated unless
skin testing confirms no allergy.
• D (Doxycycline): Tetracycline; safe.
• E (Azithromycin): Macrolide; safe.
3. A 45-year-old HIV-positive patient (CD4 count 50 cells/µL) presents with
confusion, headache, fever, and multiple ring-enhancing brain lesions on MRI.
What is the most likely cause?
A) Cryptococcus neoformans
B) Toxoplasma gondii
C) Mycobacterium tuberculosis
pg. 2
,3
D) Progressive multifocal leukoencephalopathy (PML)
E) Herpes simplex virus encephalitis
: Correct Answer : B
Full Rotation & Rationale:
• A (Cryptococcus): Causes meningoencephalitis with soap-bubble lesions in
basal ganglia, not typically ring-enhancing.
• B (Toxoplasma gondii): Correct. In AIDS with CD4 <100, the most common
cause of ring-enhancing lesions is reactivated Toxoplasma encephalitis.
• C (M. tuberculosis): Can cause tuberculomas with ring enhancement but
less common than toxoplasmosis in this setting.
• D (PML): Non-enhancing white matter lesions caused by JC virus.
• E (HSV encephalitis): Temporal lobe involvement, hemorrhagic; not
CD4-dependent.
4. A 4-year-old child presents with high fever, difficulty swallowing, drooling,
and an erythematous throat with a grayish-white membrane that bleeds when
scraped. What is the most likely cause?
A) Epstein-Barr virus
B) Corynebacterium diphtheriae
C) Streptococcus pyogenes
D) Respiratory syncytial virus
E) Bordetella pertussis
: Correct Answer : B
Full Rotation & Rationale:
• A (EBV): Exudative pharyngitis but no tough membrane that bleeds.
• B (C. diphtheriae): Correct. Pseudomembrane that bleeds on removal, bull
neck, and potential myocarditis/neuropathy from exotoxin.
• C (S. pyogenes): Strep throat with erythema and exudate but not a
tenacious membrane.
pg. 3
, 4
• D (RSV): Bronchiolitis in infants.
• E (B. pertussis): Paroxysmal coughing.
5. Which antibiotic works by inhibiting the 50S ribosomal subunit and is highly
associated with pseudomembranous colitis?
A) Clindamycin
B) Doxycycline
C) Gentamicin
D) Vancomycin
E) Ciprofloxacin
: Correct Answer : A
Full Rotation & Rationale:
• A (Clindamycin): Correct. Clindamycin inhibits 50S and is strongly linked
to C. difficile colitis.
• B (Doxycycline): 30S inhibitor.
• C (Gentamicin): 30S inhibitor; not a high risk for C. diff.
• D (Vancomycin): Treats C. diff.
• E (Ciprofloxacin): DNA gyrase inhibitor; can cause C. diff but clindamycin is
more classic.
6. A 25-year-old woman with dysuria, urinary frequency, and suprapubic
tenderness has a urine dipstick positive for leukocyte esterase and nitrite. What
is the most common causative organism?
A) Proteus mirabilis
B) Klebsiella pneumoniae
C) Escherichia coli
D) Pseudomonas aeruginosa
E) Enterococcus faecalis
pg. 4
COMSAE PHASE 1 FORM 112 PRACTICE EXAM — 176
QUESTIONS WITH FULL ROTATION RATIONALES
SECTION 1: MICROBIOLOGY & PHARMACOLOGY (Q1–40)
1. A 20-year-old college student presents with a sore throat, fever, and posterior
cervical lymphadenopathy. Examination reveals exudative tonsillitis and
splenomegaly. A complete blood count shows lymphocytosis with atypical
lymphocytes. Which of the following medications should be avoided due to risk
of a severe rash?
A) Penicillin V
B) Amoxicillin
C) Azithromycin
D) Clindamycin
E) Cephalexin
: Correct Answer : B
Full Rotation & Rationale:
• A (Penicillin V): Penicillin V is the treatment of choice for confirmed group
A streptococcal pharyngitis and does not commonly cause a rash in EBV
infection. However, the classic drug associated with a morbilliform rash in
EBV is ampicillin/amoxicillin.
• B (Amoxicillin): Correct. In patients with Epstein-Barr virus (infectious
mononucleosis), administration of amoxicillin (or ampicillin) causes a
characteristic, non-allergic maculopapular rash in up to 90% of cases. This is
not a true allergy but a Type IV hypersensitivity. Therefore, amoxicillin
should be avoided.
• C (Azithromycin): Macrolide; not associated with EBV-induced rash.
• D (Clindamycin): Lincosamide; not associated with EBV rash but carries risk
of C. difficile colitis.
pg. 1
,2
• E (Cephalexin): First-generation cephalosporin; may have cross-reactivity in
penicillin-allergic patients but does not cause the classic EBV rash.
2. A 65-year-old man with COPD is hospitalized with fever, productive cough,
and a right lower lobe infiltrate. Gram stain shows numerous neutrophils and
lancet-shaped gram-positive diplococci. He has a history of anaphylaxis after
amoxicillin. Which antibiotic is contraindicated?
A) Levofloxacin
B) Vancomycin
C) Cefazolin
D) Doxycycline
E) Azithromycin
: Correct Answer : C
Full Rotation & Rationale:
• A (Levofloxacin): Fluoroquinolone; safe in penicillin allergy.
• B (Vancomycin): Glycopeptide; no beta-lactam cross-reactivity.
• C (Cefazolin): Correct. Cephalosporins share a beta-lactam ring with
penicillins; cross-reactivity occurs in ~1-10% of penicillin-allergic patients.
With anaphylaxis to amoxicillin, cephalosporins are contraindicated unless
skin testing confirms no allergy.
• D (Doxycycline): Tetracycline; safe.
• E (Azithromycin): Macrolide; safe.
3. A 45-year-old HIV-positive patient (CD4 count 50 cells/µL) presents with
confusion, headache, fever, and multiple ring-enhancing brain lesions on MRI.
What is the most likely cause?
A) Cryptococcus neoformans
B) Toxoplasma gondii
C) Mycobacterium tuberculosis
pg. 2
,3
D) Progressive multifocal leukoencephalopathy (PML)
E) Herpes simplex virus encephalitis
: Correct Answer : B
Full Rotation & Rationale:
• A (Cryptococcus): Causes meningoencephalitis with soap-bubble lesions in
basal ganglia, not typically ring-enhancing.
• B (Toxoplasma gondii): Correct. In AIDS with CD4 <100, the most common
cause of ring-enhancing lesions is reactivated Toxoplasma encephalitis.
• C (M. tuberculosis): Can cause tuberculomas with ring enhancement but
less common than toxoplasmosis in this setting.
• D (PML): Non-enhancing white matter lesions caused by JC virus.
• E (HSV encephalitis): Temporal lobe involvement, hemorrhagic; not
CD4-dependent.
4. A 4-year-old child presents with high fever, difficulty swallowing, drooling,
and an erythematous throat with a grayish-white membrane that bleeds when
scraped. What is the most likely cause?
A) Epstein-Barr virus
B) Corynebacterium diphtheriae
C) Streptococcus pyogenes
D) Respiratory syncytial virus
E) Bordetella pertussis
: Correct Answer : B
Full Rotation & Rationale:
• A (EBV): Exudative pharyngitis but no tough membrane that bleeds.
• B (C. diphtheriae): Correct. Pseudomembrane that bleeds on removal, bull
neck, and potential myocarditis/neuropathy from exotoxin.
• C (S. pyogenes): Strep throat with erythema and exudate but not a
tenacious membrane.
pg. 3
, 4
• D (RSV): Bronchiolitis in infants.
• E (B. pertussis): Paroxysmal coughing.
5. Which antibiotic works by inhibiting the 50S ribosomal subunit and is highly
associated with pseudomembranous colitis?
A) Clindamycin
B) Doxycycline
C) Gentamicin
D) Vancomycin
E) Ciprofloxacin
: Correct Answer : A
Full Rotation & Rationale:
• A (Clindamycin): Correct. Clindamycin inhibits 50S and is strongly linked
to C. difficile colitis.
• B (Doxycycline): 30S inhibitor.
• C (Gentamicin): 30S inhibitor; not a high risk for C. diff.
• D (Vancomycin): Treats C. diff.
• E (Ciprofloxacin): DNA gyrase inhibitor; can cause C. diff but clindamycin is
more classic.
6. A 25-year-old woman with dysuria, urinary frequency, and suprapubic
tenderness has a urine dipstick positive for leukocyte esterase and nitrite. What
is the most common causative organism?
A) Proteus mirabilis
B) Klebsiella pneumoniae
C) Escherichia coli
D) Pseudomonas aeruginosa
E) Enterococcus faecalis
pg. 4
