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Lithium toxicity from thiazide — USMLE Step 3 MCQ

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HardPsychiatryLithium toxicity from thiazideUSMLE Step 3

A 25-year-old taking valproate presents with somnolence and vomiting after a dose increase. Ammonia is 186 micromol/L, valproate is 145 mg/L, pH is normal, liver aminotransferases are mildly elevated, and CT head is normal. Which treatment is most appropriate?

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Correct answer: E — Stop valproate and give intravenous L-carnitine with supportive monitoring

The best answer is “Stop valproate and give intravenous L-carnitine with supportive monitoring”. This is valproate-associated hyperammonemic encephalopathy. Drug cessation and IV L-carnitine are appropriate. Dialysis is reserved for more extreme levels, shock, severe acidosis, cerebral edema, or refractory deterioration; lactulose and unrelated antidotes do not address the toxicity. The alternatives are less suitable because they mistime the intervention, omit a necessary component, or apply treatment for a different physiologic problem; the stem's decisive findings determine the sequence.

Reference: NCBI Bookshelf, Valproate Toxicity: https://www.ncbi.nlm.nih.gov/sites/books/NBK560898/