Duloxetine is a potent serotonin and noradrenaline re-uptake inhibitor that is used for the management of major depressive disorder and diabetic neuropathic pain. The common adverse effects are nausea, dry mouth, fatigue, dizziness, somnolence, anorexia, constipation, and hyperhidrosis. The cases of hyponatremia induced by duloxetine have rarely been reported. Here, we present the case of a 75-year-old male patient who developed rapid-onset and severe hyponatremia after low-dose duloxetine treatment. In the result of laboratory investigations syndrome of inappropriate antidiuretic hormone was diagnosed and then duloxetine treatment was discontinued. Serum sodium normalized within 5 days. We suggest that elderly patients treated with duloxetine should be closely monitored for hyponatremia during duloxetine treatment particularly in the first days of treatment.
