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Difficulty: EasyPharmacologic Interventions

A 24-year-old woman comes to the clinic reporting a 2-day history of painful urination, increased urinary frequency, and suprapubic discomfort. She has no fever, flank pain, or vaginal discharge. Her medical history is notable for a severe anaphylactic reaction (hives and bronchospasm) to amoxicillin during childhood. Vital signs are within normal limits. Urinalysis is positive for leukocyte esterase and nitrites. Which of the following is the most appropriate empiric pharmacologic intervention for this patient?

  1. NitrofurantoinAnswer
  2. B
    Amoxicillin-clavulanate
  3. C
    Cephalexin
  4. D
    Moxifloxacin
  5. E
    Azithromycin

Answer

Nitrofurantoin is the most appropriate empiric therapy.
Nitrofurantoin is a first-line antibiotic for uncomplicated cystitis. It achieves high concentrations in the urinary tract and is highly effective against common uropathogens, including Escherichia coli. Crucially, as a nitrofuran antibiotic, it has no structural relationship to beta-lactams and is completely safe to administer to a patient with a severe anaphylactic allergy to penicillin.

Step-by-Step Solution

1
Identify the clinical syndrome.
The patient has dysuria, frequency, and suprapubic pain without systemic signs (fever, flank pain), consistent with uncomplicated cystitis.
Accurate diagnosis determines the required spectrum of antimicrobial coverage.
2
Review the patient's medical history for contraindications.
The patient has a history of anaphylaxis to amoxicillin.
A history of IgE-mediated anaphylaxis precludes the use of penicillins and warrants strict avoidance of related beta-lactams with high cross-reactivity, such as first-generation cephalosporins.
3
Select the appropriate pharmacologic intervention.
Nitrofurantoin is chosen as it is a first-line agent for uncomplicated cystitis and has no cross-reactivity with beta-lactams.
It achieves high concentrations in the urine, covers common uropathogens, and is safe given the patient's allergy profile.

Key Concept

In patients with uncomplicated cystitis and a severe, IgE-mediated penicillin allergy, nitrofurantoin is a safe and highly effective first-line pharmacologic intervention. Medications with cross-reactivity (like first-generation cephalosporins) or inadequate urinary concentration (like moxifloxacin) must be avoided.
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Pharmacologic Interventions

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