A review on hyponatremia associated with SSRIs, reboxetine and venlafaxine.

Hyponatremia, defined as serum sodium below 135 mmol/l, is a potentially life-threatening condition and was shown to be more frequent in elderly and psychiatric patients. In the last years numerous case reports on SSRI- and venlafaxine-induced hyponatremia were published indicating a higher incidence than previously thought. Only few studies have been performed and the incidence reported varies widely from 4.6/1000 people to 25%. It is still unclear if any single SSRI shows a higher incidence of hyponatremia than the others. Some data suggest that venlafaxine may have a stronger association to hyponatremia than SSRIs. Risk factors include age, female sex, low body mass index, severe physical illness, history of former hyponatremia and co-medications known to induce hyponatremia, especially thiazide diuretics. Symptoms of hyponatremia are usually neuropsychiatric (e.g. restlessness, lethargy, cognitive impairment), and any worsening in psychiatric symptoms in patients with a corresponding risk-profile receiving SSRIs or venlafaxine should give cause to check serum electrolytes. Usually SSRI-induced hyponatremia occurs within approximately 30 days and is reported to improve after withdrawal of the drug. Further controlled studies to confirm the true incidence of hyponatremia due to SSRI or venlafaxine and to define predictors more precisely are needed.