Citalopram Therapy as a Risk Factor for Symptomatic Hyponatremia Caused by the Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH)

We report the case of an 81-year old woman with stupor, confusion, somnolence, vomiting, and reduced food intake for 5 days. Laboratory investigations revealed low serum concentrations of sodium and potassium with a serum osmolality of 225 mOsm/kg H₂O in the face of an inappropriately concentrated urine with an osmolality in the normal range, suggesting the syndrome of inappropriate antidiuretic hormone secretion (SIADH) in the absence of renal insufficiency, adrenal insufficiency, and hypothyroidism. Careful drug evaluation revealed amitriptyline and citalopram as possible inciters of antidiuretic hormone secretion. Subsequently, these drugs were withdrawn. Under continuous sodium substitution and fluid restriction serum sodium normalized and the patient’s symptoms resolved. She was fully alert by day 15. We conclude that hyponatremia secondary to SIADH was the cause of the patient’s neurologic symptoms. Clinicians should be aware of this possible side effect of central acting agents such as amitriptyline and citalopram, drugs that are often used to treat elderly patients suffering from depression or chronic pain.

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