Glimepiride and Syndrome of Inappropriate Antidiuretic Hormone Secretion

Syndrome of Inappropriate Antidiuretic hormone secretion(SIADH) is characterized by presence of hyponatremia without dehydration, increased renal excretion of sodium, low plasma osmolality, high urine osmolarity and detectable plasma antidiuretic hormone; in presence of normal adrenal and renal function. CASE REPORT: A 67 years old female with type 2 diabetes mellitus had been treated with Metformin 500mg daily along with Glimepiride 2mg daily for the past two years. She presented to the hospital with history of altered sensorium and unresponsiveness. The clinical examination, radiological data did not reveal any significant neurological abnormality and the biochemical data denied the presence of dehydration, renal and cardiac insufficiency. The hormonal tests ruled out hypothyroidism, cortisol deficiency and ACTH deficiency. The patient was not on any diuretics. Her random blood sugar level was 36mg/Dl, serum Na was 128 mmol/L, serum creatinine 0.6 mg/Dl, plasma osmolarity of 260mOsm/kg, urinary sodium significantly increased to 70 mmol/L and high urinary osmolarity of greater than 300mOsm/kg. The patient was diagnosed having SIADH; having ruled out all the other possibilities of hyponatremia along with hypoglycemia, the cause was attributed to glimepiride. She was taken off glimepiride immediately, and her serum sodium promptly increased to 133 mmol/L after 4 days.