Medication-Induced Severe Hyponatremia After Elective Surgery in a Patient With Known Arginine Vasopressin Deficiency.

Arginine vasopressin deficiency (AVP-D) is a rare disorder associated with a considerable risk of dysnatremia. This case involves a 59-year-old woman with idiopathic AVP-D and secondary hypocortisolemia, who developed severe hyponatremia after elective knee replacement. Postoperative pain management included nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids. On day 4 of her admission, serum sodium concentration was 128 mEq/L (SI: 128 mmol/L) (reference range, 135-145 mEq/L [SI: 135-145 mmol/L]), but this was not reviewed. Feeling unwell that evening, she self-administered 200 mcg desmopressin; the next morning her sodium was 119 mEq/L (SI: 119 mmol/L); despite withholding all regular desmopressin doses for that day and the commencement of the expectant polyuria, hours later her sodium fell to 113 mEq/L (SI: 113 mmol/L). Emergency treatment involved fluid restriction and hypertonic saline, raising the sodium to 120 mEq/L (SI: 120 mmol/L) in 6 hours. Desmopressin 100 mcg was then restarted to clamp rapid overcorrection. Over 30 hours, sodium normalized with further desmopressin given as polyuria recurred: no neurological issues arose. Literature review found 14 cases of NSAIDs and opioids causing acute and severe hyponatremia in those taking desmopressin, highlighting the importance for clinicians and patients to be aware of these medication interactions.