Toxicology USMLE Step 1 Practice Question
A 56-year-old woman with bipolar disorder on lithium presents with coarse tremor, ataxia, and confusion after 3 days of vomiting and diarrhea. Vital signs show BP 108/72, HR 102, RR 18, temp 37.8°C, SpO2 98%. Serum lithium level is 2.1 mEq/L (therapeutic: 0.6-1.2). She denies recent NSAIDs or ACE inhibitors. Urinalysis reveals low specific gravity. Which mechanism most likely precipitated her toxicity?
Answer choices
- AUse of mesna
- BVolume depletion reducing renal clearanceCorrect answer
- CUse of methylene blue
- DConcurrent naloxone administration
- EHigh dietary sodium intake
- FIncreased glomerular filtration rate enhancing lithium reabsorption
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