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Difficulty: EasyPharmacologic Interventions

A 28-year-old man comes to the clinic for evaluation of a painless ulcer on his penis that appeared one week ago. He has no other symptoms and feels well. He is sexually active with multiple partners. His medical history is significant for an episode of severe anaphylaxis, including throat swelling and hypotension, after receiving amoxicillin at age 12. He takes no daily medications. Vital signs are within normal limits. Physical examination reveals a 1.5-cm, indurated, painless ulcer with a clean base on the glans penis. There is bilateral, non-tender inguinal lymphadenopathy. Dark-field microscopy of a sample from the ulcer exudate shows motile spirochetes. Which of the following is the most appropriate pharmacologic intervention for this patient?

  1. Oral doxycyclineAnswer
  2. B
    Intramuscular penicillin G benzathine
  3. C
    Intramuscular ceftriaxone
  4. D
    Oral azithromycin
  5. E
    Inpatient penicillin desensitization followed by intramuscular penicillin G benzathine

Answer

Oral doxycycline is the most appropriate treatment for primary syphilis in a non-pregnant adult with a severe penicillin allergy.
The correct intervention is oral doxycycline. The patient has confirmed primary syphilis (Treponema pallidum infection), for which the standard treatment is intramuscular penicillin G benzathine. However, this patient has a history of severe, IgE-mediated anaphylaxis (throat swelling, hypotension) to amoxicillin. Therefore, penicillin is absolutely contraindicated. According to the Centers for Disease Control and Prevention (CDC) sexually transmitted infections treatment guidelines, the preferred alternative for treating primary, secondary, or early latent syphilis in a non-pregnant adult with a severe penicillin allergy is oral doxycycline for 14 days. This avoids the risk of allergic cross-reactivity and is highly effective at curing the infection.

Step-by-Step Solution

1
Establish the primary diagnosis based on clinical and laboratory findings.
The patient has primary syphilis, confirmed by a painless chancre and positive dark-field microscopy for motile spirochetes.
Identifying the infectious agent is the first step in determining appropriate antimicrobial therapy.
2
Evaluate the patient's medication history for contraindications to standard therapy.
The standard first-line treatment, intramuscular penicillin G benzathine, is absolutely contraindicated due to a history of severe anaphylaxis to amoxicillin.
Administering penicillin to a patient with a confirmed IgE-mediated severe allergy can cause life-threatening anaphylactic shock.
3
Select the best alternative pharmacologic intervention according to current treatment guidelines.
Oral doxycycline for 14 days is the standard recommended alternative for primary syphilis in non-pregnant adults with a penicillin allergy.
Doxycycline is highly effective for early syphilis and avoids the risk of cross-reactivity seen with cephalosporins in severe penicillin-allergic patients.

Key Concept

In non-pregnant adult patients with primary, secondary, or early latent syphilis who have a severe penicillin allergy, oral doxycycline is the preferred pharmacologic intervention.
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Topics

Pharmacologic Interventions

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