<prompt> A 42-year-old man is on amitriptyline for depression. Recently he has been feeling more lethargic and unwell. His clinical examination is normal. Serum sodium is 125 mEqL and osmolality is 260 mOsmkg, and urine sodium is 40 mEqL and osmolality is 450 mOsmkg.For the above patient with hyponatremia, select the most likely diagnosis.congestive heart failure CHFextrarenal sodium and fluid lossesSIADHpolydipsia  <response>: Amitriptyline is one of the psychoactive drugs that cause SIADH. Others include phenothiazines, serotonin reuptake inhibitors, and monoamine oxidase inhibitors MAOIs. Antineoplastic drugs such as vincristine and cyclophosphamide also cause SIADH, as does the hypoglycemic agent chlorpropamide. 