A 50-year-old man started on carbamazepine for trigeminal neuralgia presents six weeks later with fatigue and nausea. Serum sodium is 122 mEq/L, urine osmolality is elevated, and euvolemia is present. The most likely explanation is:
- A Carbamazepine-induced syndrome of inappropriate ADH secretion ✓
- B Carbamazepine-induced nephrogenic diabetes insipidus
- C Carbamazepine-associated pseudohypoaldosteronism
- D Carbamazepine-triggered cerebral salt wasting
Correct answer: A. Carbamazepine-induced syndrome of inappropriate ADH secretion
Explanation
Carbamazepine potentiates ADH action at the renal collecting duct and can cause true SIADH with euvolemic hypo-osmolar hyponatremia and concentrated urine. Oxcarbazepine carries an even higher risk of hyponatremia than carbamazepine. Diabetes insipidus would produce dilute urine with hypernatremia, which kills option B, and cerebral salt wasting features volume depletion rather than euvolemia.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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