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Difficulty: EasyInfectious Diseases

Match the following classic infectious disease clinical presentations with the most appropriate first-line antimicrobial therapy.

  • A 20-year-old college student with fever, neck stiffness, and cerebrospinal fluid analysis revealing gram-negative diplococci.Intravenous ceftriaxone
  • A 30-year-old pregnant woman in her first trimester who presents with an expanding targetoid rash (erythema migrans) after a tick bite.Oral amoxicillin
  • A 45-year-old man with an indurated, painless ulcer on his penis and bilateral inguinal lymphadenopathy.Intramuscular penicillin G benzathine
  • A 25-year-old woman with dysuria, increased urinary frequency, and a positive nitrite test on urinalysis, with no fever or flank pain.Oral nitrofurantoin

Answer

Gram-negative diplococci (meningitis) pairs with IV ceftriaxone. Lyme disease in pregnancy pairs with oral amoxicillin. Primary syphilis pairs with IM penicillin G benzathine. Uncomplicated cystitis pairs with oral nitrofurantoin.
Each clinical scenario presents a classic infectious disease that requires a specific first-line antimicrobial. Meningococcal meningitis requires CNS-penetrating IV ceftriaxone. Lyme disease in pregnancy requires amoxicillin to avoid tetracycline teratogenicity. Primary syphilis is definitively treated with IM penicillin G benzathine. Uncomplicated cystitis is safely managed with oral nitrofurantoin.

Step-by-Step Solution

1
Identify the likely pathogen and disease state for the first presentation.
Gram-negative diplococci in CSF indicates Neisseria meningitidis meningitis.
Recognizing the pathogen is necessary to select the appropriate targeted therapy.
2
Determine the appropriate treatment for meningococcal meningitis.
Intravenous ceftriaxone.
Third-generation cephalosporins are the standard of care for empiric and targeted therapy of N. meningitidis meningitis.
3
Identify the disease and patient constraints for the second presentation.
Erythema migrans indicates Lyme disease in a pregnant patient.
Pregnancy alters the standard treatment algorithm for early Lyme disease.
4
Select the appropriate alternative treatment for Lyme disease in pregnancy.
Oral amoxicillin.
Doxycycline is teratogenic, making amoxicillin the preferred safe alternative.
5
Identify the disease and stage for the third presentation.
Painless chancre indicates primary syphilis.
Accurate staging dictates the required dosage and duration of penicillin therapy.
6
Select the standard treatment for primary syphilis.
Intramuscular penicillin G benzathine.
A single dose of long-acting penicillin is curative for primary syphilis.
7
Identify the diagnosis for the fourth presentation.
Symptoms and positive nitrites without systemic signs indicate uncomplicated cystitis.
Differentiating uncomplicated cystitis from pyelonephritis dictates oral versus systemic/broad therapy.
8
Select the appropriate first-line therapy for uncomplicated cystitis.
Oral nitrofurantoin.
Nitrofurantoin concentrates well in the urine and is a preferred first-line agent.

Key Concept

Selection of first-line targeted antimicrobial therapy for common infectious diseases while accounting for patient-specific contraindications.
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Topics

Infectious Diseases

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