300
A 70-year-old male with hypertension, benign prostatic hyperplasia, depression, and well-controlled diabetes mellitus sees you because of increasing fatigue. His medical history also includes stent placement for coronary artery disease. A physical examination is unremarkable except for decreased peripheral pulses. A CBC, basic metabolic profile, hemoglobin A1c level, free T4 level, and TSH level are all normal, except for a serum sodium level of 125 mEq/L (N 135–145). His serum osmolality is 268 mOsm/kg (N 275–290). His urine sodium level is 50 mEq/L (N <20) and his urine osmolality is 300 mOsm/kg.
Which one of the patient’s medications is most likely to cause this problem?
A) Losartan (Cozaar)
B) Tamsulosin (Flomax)
C) Metformin (Glucophage)
D) Atorvastatin (Lipitor)
E) Sertraline (Zoloft)
ANSWER: E
In patients who are euvolemic but have hyponatremia, decreased serum osmolality, and elevated urine osmolality, the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is likely. Other causes to rule out include thyroid disorders, adrenal insufficiency, and diuretic use. Renal function has to be normal as well. Common drugs that cause SIADH include SSRIs (particularly in patients over 65), chlorpropamide, barbiturates, carbamazepine, opioids, tolbutamide, vincristine, diuretics, and NSAIDs. Treatment of the problem consists of discontinuing the offending drug. Temporary fluid restriction may also be required.