Hyponatremia in elderly psychiatric inpatients – case characteristics in a natural setting

Background: Hyponatremia (HN) is a well recognized side effect in psychopharmacological treatment. Old age is one of the most important risk factors for HN. Aims: To evaluate incidence, risk factors, and causes of HN in elderly psychiatric patients in a natural setting. Methods: Cases of HN (Na <135 mmol/L) in psychiatric inpatients over 55 years of age occuring during a 18-month period (July 2005 through December 2006) were identified using a laboratory database. Demographic, diagnostic, and treatment data were obtained by a chart review. Results: HN occurred in 74 of 1334 patients (5.5%, aged 71.5±10.3yrs, 86% female). Diagnoses included Major depression (46 cases), dementia (26), and schizophrenia/schizoaffective disorders (18). 61 patients received treatment with a drug potentially associated with HN as a side effect, mainly antidepressants (36 cases). HN occurred most often with mirtazapine (9 cases), venlafaxine (7), and duloxetine (5). Other potentially contributing drugs were the mood stabilizer carbamazepine (14), antihypertensives such as loop diuretics (33), and ACE inhibitors (22). The lowest tertile of sodium plasma levels was most often associated with combination therapy of two or more of the mentioned substances. Conclusions: In this natural setting of elderly psychiatric inpatients, female gender, antidepressant (not necessarily SSRI alone) and combination drug therapy were the most prevalent risk factors for treatment emergent HN.