Duloxetine-induced hyponatraemia in a patient with hypocortisolaemia

Duloxetine-induced hyponatraemia is a known adverse effect that can lead to potentially life-threatening complications. In addition, hypocortisolaemia is associated with the development of hyponatraemia. Here, we report a case of severe hyponatraemia rapidly presenting after duloxetine treatment in a patient with hypocortisolaemia. A 75-year-old man administered hydrocortisone for the treatment of hypocortisolaemia induced by a Rathke's cleft cyst was admitted for anorexia 3 days after the initiation of duloxetine therapy. Laboratory findings showed severe hyponatraemia, hypo-osmolality, concentrated urine, and increased urine sodium. Because the syndrome of inappropriate antidiuretic hormone was diagnosed, duloxetine was ceased. Following admission to the hospital, endocrinological analyses revealed mild hypocortisolaemia, possibly due to low adherence to hydrocortisone replacement therapy. By the sixth day after admission, the patient's hyponatraemia, serum osmolality, and urine osmolality had improved. This case suggests that health-care physicians should be aware of the possibility of duloxetine-related hyponatraemia, particularly in patients with hypocortisolaemia.