Desmopressin, an antidiuretic hormone analogue, is commonly prescribed for the treatment of nocturnal enuresis in elderly patients. Due to its favorable tolerance and significant reduction in nocturia, desmopressin is increasingly used in this population. However, long-term use may increase the risk of severe hyponatremia.

We present the case of a 76-year-old male patient who developed severe hyponatremia (Na <115 mEq/L) induced by desmopressin.

The patient had a history of lower urinary tract symptoms (LUTS) and had been taking desmopressin 100 mcg daily for one year. He visited our outpatient clinic with complaints of nausea, vomiting, abdominal pain, and muscle weakness for two days. Physical and neurological examinations were unremarkable, but laboratory tests revealed a sodium level of 114 mEq/L. Following gradual electrolyte correction, his sodium level improved to 128 mEq/L, and he fully recovered without complications. After discharge, his desmopressin dose was reduced to 50 mcg daily, and his sodium levels stabilized between 130 and 135 mEq/L without further discomfort.

Desmopressin has been reported to cause mild hyponatremia (130–135 mEq/L) in 15% of patients and severe hyponatremia in approximately 5% of adult patients. Hyponatremia is associated with symptoms such as headache, nausea, vomiting, dizziness, malaise, loss of consciousness, and, in severe cases, death. Studies have shown that long-term desmopressin use can lead to significant hyponatremia within six months, even in patients who initially had normal sodium levels. The recommended starting dose is 50–100 mcg daily, with a lower initial dose of 25–50 mcg being more appropriate for elderly patients. Regular serum sodium monitoring, at least every six months, is advised. In elderly patients, more stringent follow-up is necessary to minimize the risk of complications.