Antimicrobials USMLE Step 1 Practice Question
A 71-year-old man with chronic kidney disease (eGFR 25 mL/min/1.73m²) presents with severe bilateral Achilles tendon pain on day 3 of levofloxacin 500 mg daily for urinary tract infection. Vital signs show BP 88/52, HR 118, RR 20. He experienced syncope this morning. Serum creatinine is 4.2 mg/dL. ECG reveals prolonged QTc interval. He denies chest pain or palpitations. Which mechanism best explains his syncope?
Answer choices
- AFluoroquinolone-induced tendinopathy directly damages the cerebellum
- BThe patient experienced a vasovagal response to tendon pain
- CLevofloxacin accumulation prolongs QT interval, predisposing to torsades de pointesCorrect answer
- DLevofloxacin directly depresses myocardial contractility
- EChronic kidney disease alone is sufficient to cause syncope in elderly patients
- FLevofloxacin-induced hypomagnesemia decreases renal potassium reabsorption, causing severe hypokalemia
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