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Difficulty: EasyInfectious Diseases

Match each classic infectious disease clinical presentation with its most appropriate first-line antimicrobial therapy.

  • A 25-year-old with an expanding annular rash with central clearing after hiking in the northeastern United StatesOral doxycycline
  • A 32-year-old with a painless, indurated penile ulcer and non-tender inguinal lymphadenopathyIntramuscular benzathine penicillin G
  • A 22-year-old with yellow-green, frothy vaginal discharge and flagellated motile organisms on microscopyOral metronidazole
  • A 28-year-old with purulent urethral discharge and intracellular gram-negative diplococci on Gram stainIntramuscular ceftriaxone

Answer

The expanding annular rash matches with oral doxycycline (Lyme disease), the painless penile ulcer matches with intramuscular benzathine penicillin G (primary syphilis), the frothy vaginal discharge matches with oral metronidazole (trichomoniasis), and the purulent urethritis matches with intramuscular ceftriaxone (gonorrhea).
Each clinical scenario has a highly specific, guideline-directed first-line therapy. Erythema migrans (Lyme disease) is treated with oral doxycycline. A painless chancre (primary syphilis) is treated with intramuscular benzathine penicillin G. Trichomoniasis requires oral metronidazole. Gonococcal urethritis requires intramuscular ceftriaxone.

Step-by-Step Solution

1
Identify the underlying pathogen for the expanding annular rash (erythema migrans).
Early localized Lyme disease (Borrelia burgdorferi), which requires oral doxycycline.
Erythema migrans is pathognomonic for Lyme disease, and doxycycline is the preferred first-line antibiotic for non-pregnant adults.
2
Identify the pathogen for the painless indurated ulcer (chancre).
Primary syphilis (Treponema pallidum), which requires intramuscular benzathine penicillin G.
Benzathine penicillin G provides prolonged, low-dose therapy which is highly effective against Treponema pallidum.
3
Identify the pathogen for the frothy vaginal discharge with motile organisms.
Trichomonas vaginalis, which requires oral metronidazole.
Metronidazole provides excellent coverage against this anaerobic protozoan.
4
Identify the pathogen for purulent urethritis with gram-negative diplococci.
Neisseria gonorrhoeae, which requires intramuscular ceftriaxone.
Ceftriaxone is the recommended first-line therapy for uncomplicated gonococcal infections due to widespread resistance to other agents.

Key Concept

First-line targeted antimicrobial therapy for classic infectious disease presentations.
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Topics

Infectious Diseases

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