Antimicrobials USMLE Step 1 Practice Question
A 73-year-old hospitalized man with community-acquired pneumonia is treated with IV ceftriaxone. Two weeks into therapy, he develops watery diarrhea, cramping abdominal pain, and fever (38.5°C). Vital signs show HR 102/min, BP 128/82 mmHg, RR 18/min. Stool testing is positive for Clostridioides difficile toxin. WBC is elevated at 14,500/μL. He denies recent antibiotic use prior to ceftriaxone. Which of the following most likely predisposed him to this complication?
Answer choices
- ABlockade of viral DNA polymerase
- BInhibition of fungal ergosterol synthesis
- CDirect stimulation of colonic muscarinic receptors
- DIrreversible inhibition of bacterial topoisomerase II
- EDisruption of normal gut flora by a broad spectrum beta-lactam antibioticCorrect answer
- FImpaired neutrophil chemotaxis due to complement-mediated immune suppression
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.