Chlorthalidone-induced syndrome of inappropriate secretion of antidiuretic hormone.

A 60-year-old woman who had been instructed to increase her water intake because of nephrolithiasis developed the syndrome of inappropriate secretion of antidiuretic hormone when treated with chlorthalidone for mild hypertension. Serum osmolality was 235 mOsm/kg with concomitant urine osmolality of 490 mOsm/kg. When serum sodium decreased to 110 mEq/liter, plasma antidiuretic hormone (ADH) was elevated at 30 pg/ml. The syndrome resolved when chlorthalidone was discontinued together with fluid intake restriction. Plasma ADH returned to normal (less than 0.5 pg/ml) after three days of treatment. The favorable outcome in this patient is attributed to early recognition of the syndrome, which might occur even with nonthiazide diuretics such as chlorthalidone.