The incidence of SSRI´s induced hyponatremia may occur in about 0, 5% to 32%.Recent results identified newer agents like duloxetine as a cause for hyponatremia. The risk factors for SSRI´S induced hyponatremia are: age, female sex, low body mass, using diuretics, and low levels of serum sodium.

To report a case of recurrent hyponatremia after switching from one class of antidepressant to another.

A 71-years-old women with recurrent depression disorder (treated since 6 years with different antidepressant trials) began recurrence treatment with duloxetine. Four weeks later presenting a symptomatic hyponatremia and hypokaliemia she's hospitalized. On physical examination patient was euvolemic and had no evidence of iatrogenic, malignancy, renal, hepatic, adrenal or thyroid disease. The hypothesis of duloxetine induced hyponatremia (not the hypokaliemia) was considered and duloxetine was suspended. Due to the persistence of depression, treatment with sertralina was initiated. Twenty days later Na+ was 127mEq/L, sertraline was discontinued and mianserine introduced .Patient maintained hyponatremia and developed confusion, agitation, and psychotic symptoms (mystic delirious) being admitted in a psychogeriatric inpatient unit. Antidepressant was suspended. Patient became maniac and efficient treatment with a mood stabilizer and atypical antipsychotic initiated. She was discharged after serum sodium concentration normalized, psychotic symptoms and mood disorder stabilized.

Psychiatrists should be aware from the risk of developing antidepressant-induced hyponatremia mainly in elderly patients. Electrolyte measurements concentrations should be monitored, not only in the first weeks of treatment, but throughout the full course, mainly if risk factors are present.