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Question

Difficulty: MediumInfectious Diseases

Match each clinical presentation with the most appropriate, guideline-directed primary antimicrobial therapy.

  • A 24-year-old pregnant woman in her first trimester presents with an expanding erythematous targetoid rash and mild fatigue after a recent camping trip.Oral amoxicillin
  • A 65-year-old man develops profuse, foul-smelling watery diarrhea and marked leukocytosis two weeks after completing treatment for community-acquired pneumonia.Oral fidaxomicin
  • A 30-year-old man presents with a solitary, painless, indurated penile ulcer and bilateral inguinal lymphadenopathy; non-treponemal serology is reactive.Intramuscular penicillin G benzathine
  • A 45-year-old woman with a history of injection drug use presents with high fever, a new holosystolic murmur, and blood cultures yielding methicillin-susceptible Staphylococcus aureus.Intravenous cefazolin
  • A 19-year-old college student presents with sudden-onset fever, headache, nuchal rigidity, and a rapidly spreading petechial rash; cerebrospinal fluid analysis reveals Gram-negative diplococci.Intravenous ceftriaxone

Answer

Lyme disease in pregnancy matches with oral amoxicillin; Clostridioides difficile infection matches with oral fidaxomicin; primary syphilis matches with intramuscular penicillin G benzathine; MSSA endocarditis matches with intravenous cefazolin; meningococcal meningitis matches with intravenous ceftriaxone.
Each patient presentation maps to a specific, guideline-directed antimicrobial agent. Amoxicillin is safe for Lyme disease in pregnancy. Fidaxomicin is the preferred initial treatment for C. difficile. Penicillin G benzathine is the definitive therapy for primary syphilis. Cefazolin is superior for MSSA endocarditis. Ceftriaxone provides necessary CNS penetration for meningococcal meningitis.

Step-by-Step Solution

1
Analyze the first patient's targetoid rash and pregnant status.
Identifies early localized Lyme disease requiring pregnancy-safe antibiotics.
Doxycycline is teratogenic, making amoxicillin the safest effective choice.
2
Evaluate the second patient's post-antibiotic diarrhea.
Identifies an initial episode of Clostridioides difficile infection.
Current guidelines recommend oral fidaxomicin over vancomycin for primary episodes to decrease recurrence.
3
Assess the third patient's painless penile ulcer and reactive serology.
Diagnoses primary syphilis.
Treponema pallidum remains exquisitely sensitive to penicillin G benzathine.
4
Recognize the fourth patient's presentation of right-sided infective endocarditis.
Identifies MSSA endocarditis.
Requires beta-lactam therapy such as intravenous cefazolin for optimal bactericidal activity.
5
Diagnose the fifth patient's petechial rash and Gram-negative diplococci in CSF.
Identifies meningococcal meningitis.
Requires a third-generation cephalosporin like intravenous ceftriaxone for effective central nervous system penetration.

Key Concept

Targeted antimicrobial selection based on pathogen profile, site of infection, and host factors.
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Topics

Infectious Diseases

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