SSRIs and Hyponatraemia

Increasing age, certain medications such as diuretics, disease processes such as malignant neoplasm and schizophrenia, and a history of hyponatraemia or polydipsia may predispose patients to the development of hyponatraemia. In addition, certain psychotropic medications, including TCAs, MAOIs, carbamazepine, trazodone and neuroleptics, may predispose to hyponatraemia, yet a causative role for most has not been firmly established and the effect is most likely to be more idiosyncratic. The SSRIs have been associated with hyponatraemia in a small number of case reports. The mean age and sex of patients in reported cases is over 70 years and predominantly female, and patients were often receiving concomitant diuretic therapy. The frequency of hyponatraemia in elderly female patients receiving fluoxetine has been estimated to be as high as eight per 1000. The risk of developing hyponatraemia appears to be highest during the first few weeks of treatment. Because of the potential seriousness of hyponatraemia, if an elderly patient receiving an SSRI develops unexplained symptoms during the first few weeks of therapy, it is necessary to measure the serum sodium level.