Electrolyte Disorders USMLE Step 1 Practice Question
A 66-year-old man with metastatic prostate cancer presents with severe hypercalcemia (serum calcium 13.2 mg/dL). He receives IV zoledronic acid infusion. Vital signs show BP 145/92 mmHg, HR 88/min, RR 16/min, temp 37.2°C, SpO2 98% on room air. Two days later, serum calcium normalizes to 9.1 mg/dL. Renal function remains stable with creatinine 1.0 mg/dL. Which mechanism best explains the bisphosphonate's therapeutic effect?
Answer choices
- ABlockade of intestinal phosphate absorption
- BActivation of vitamin D receptors in enterocytes
- CIncreased renal calcium reabsorption in the distal tubule
- DInhibition of osteoclast-mediated bone resorptionCorrect answer
- EDirect binding of serum calcium in the bloodstream
- FStimulation of calcitonin secretion from parafollicular thyroid cells
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