A patient on hydrochlorothiazide develops hyponatraemia; which medication could contribute via SIADH?

A patient on hydrochlorothiazide develops hyponatraemia; which medication could contribute via SIADH?

• A. Acetaminophen
• B. Lisinopril
• C. Amoxicillin
• D. Carbamazepine

Answer: (D)

The main idea is drug-induced SIADH, where there is excess release or action of ADH causing water retention and dilutional hyponatremia. Carbamazepine is a classic cause of SIADH: it increases ADH secretion and/or the renal response to ADH, leading to euvolemic hyponatremia. In a patient already taking hydrochlorothiazide, which promotes sodium loss, this SIADH effect can worsen the drop in serum sodium. The other medications listed are not typically associated with SIADH as a primary mechanism, so they don’t commonly produce this pattern of hyponatremia.

The main idea is drug-induced SIADH, where there is excess release or action of ADH causing water retention and dilutional hyponatremia. Carbamazepine is a classic cause of SIADH: it increases ADH secretion and/or the renal response to ADH, leading to euvolemic hyponatremia. In a patient already taking hydrochlorothiazide, which promotes sodium loss, this SIADH effect can worsen the drop in serum sodium. The other medications listed are not typically associated with SIADH as a primary mechanism, so they don’t commonly produce this pattern of hyponatremia.