Hyponatremia is one of the electrolytic disorders most comonly observed among general hospitalized populations (2% of hospitalized patients). A form of hyponatremia is the syndrome of inappropriate antidiuretic hormone secrection (SIADH). One of its diverse causes is medication. Selective serotonine reuptake inhibitors (ISRSs) can cause hyponatremia due to SIADH, particularly among elderly population.

A 81-year-old female treated with paroxetine 20mg/day because of depression. Two weeks later she starts feeling nausea, somnolence and motor inhibition. The sodium level previous to the onset of treatment was normal but after two weeks it has decreased to 121 mEq/L, pointing to SIADH induced by ISRSs.

The incidence of hyponatremia among elderly patients treated with antidepressants of ISRSs class has increased. The prevalence varies between 0.5 and 25%. Although half of the patients are asymptomatic, the mortality is rate may reach 25%. It generally develops during the first month of treatment and is reversible between 2 and 28 days after the suspension of the ISRSs.