hydrochlorothiazide × sertraline

Thiazides are one of the commonest drug causes of hyponatremia in older adults (via an SIADH-like mechanism plus natriuresis). SSRIs add their own SIADH effect. Additive risk of severe hyponatremia (Na+ < 125 mmol/L) with confusion, seizures, and falls.

Check sodium at baseline, at 1, 2, and 4 weeks after sertraline initiation, then every 3 months. In patients over 75 with sodium < 135 mmol/L, optimize the thiazide or switch the antidepressant.