Effect of paroxetine on plasma vasopressin and water load testing in elderly individuals

Hyponatremia sometimes occurs in elderly depressed patients treated wtih a serotonin reuptake inhibitor (SRI). The cause of the hyponatremia is not ye t understood. The objective of this study was to determine the effects of p aroxetine, an SRI, on osmoregulated release of vasopressin (also termed ant idiuretic hormone) in elderly depressed patients with normal serum sodium. Four women and one man ages 61 to 74 years with a major depressive disorder were administered a water load after they had been treated with a therapeu tic dose of paroxetine for 3 to 11 months. Three healthy elderly subjects n ot receiving paroxetine served as controls. Both the patients and the contr ol subjects excreted > 90% of the ingested water and lowered urine osmolali ty to < 100 mosmol/kg. We conclude that long-term treatment with paroxetine alone does not appear to affect the ability to excrete a water load or app ropriately dilute the urine during a water load (both indices of vasopressi n function) in a small group of elderly patients without other risk factors for the development of hyponatremia.