Paroxetine-induced hyponatremia in the elderly due to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH).

This study investigated the development of hyponatremia and its underlying mechanism in elderly patients prescribed paroxetine. Patients were 15 men and women (mean age, 75.7 +/- 5.3 years) who were participants in a treatment study of late-life depression and who were without medical illness or other medications known to cause hyponatremia or alter antidiuretic hormone (ADH) secretion. Blood samples for measurement of plasma sodium, ADH, blood urea nitrogen (BUN), creatinine, glucose, and osmolality were determined prior to initiation of paroxetine (week 0) and at 2, 4, 6, and 12 weeks of treatment with paroxetine. Hyponatremia (serum sodium < 135 mEq/L) was identified in 6 of 15 patients after 2 weeks of treatment with paroxetine. Despite low plasma osmolality, ADH levels were not suppressed appropriately. Data suggest hyponatremia is a common adverse event in elderly patients prescribed paroxetine and implicates inappropriate secretion of ADH as the potential mechanism.