Antimicrobials USMLE Step 1 Practice Question
A 32-year-old woman with community-acquired pneumonia presenting with fever (38.9°C), cough, and dyspnea is prescribed azithromycin. On day 4 of therapy, she develops severe cramping abdominal pain, watery diarrhea, and fever (39.2°C). Stool testing confirms Clostridioides difficile toxin B positivity. Laboratory studies show WBC 14,500/μL. She denies recent hospitalization or prior antibiotic use. Which mechanism best explains how azithromycin increased her risk for this infection?
Answer choices
- ADisruption of normal colonic microbiota, allowing pathogenic overgrowthCorrect answer
- BDirect cytotoxic effect on intestinal epithelial cells
- CInhibition of peristalsis leading to bacterial stasis
- DIncreased gastric pH promoting bacterial colonization
- EAllergic reaction to macrolide metabolites in the colon
- FImpaired production of intestinal mucus layer through inhibition of goblet cell function
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