A 71-year-old hypertensive and diabetic male patient was seen in the outpatient clinic for routine control. On laboratory examination his serum potassium level was 5.76 mmol/l and serum sodium level was 135 mmol/l. Control serum potassium level was 5.7 mmol/l. In past medical history he was prescribed telmisartan/hydrochlorothiazide combination (80 mg/12.5 mg) 1 month ago for treatment of hypertension. His other medications included nifedipine, fluvastatin sodium, aspirin, pioglitazone and subcutaneous pre-mixed insülin analog (two times a day). He was hospitalised for investigation of his hyperkalemia. His creatinine clearance was normal for age and adrenal insufficiency was ruled out with an ACTH stimulation test. A few days after his hospitalisation, his serum sodium levels began to decrease steadily from 135 mmol/l to 119 mmol/l and the patient became lethargic. With a preliminary diagnosis of hyporeninemic hypoaldosteronism secondary to his 18 year-old history of type 2 diabetes mellitus, fludrocortisone 1×100 μg was started. After 3 days of fludrocortisone treatment he was still hyperkalemic and hyponatremic, hence telmisartan/hydrochlorotiazide 80/12.5 mg treatment was stopped and fludrocortisone dose was raised to 150 μg. He was kept under observation until his serum potassium levels stabilised around 4.5 mmol/l and was discharged with fludrocortisone 1×100 μg. Hyperkalemia and hyponatremia are not reported in the side effects section of telmisartan/hydrochlorotiazide. In English literature in just one study telmisartan/hydrochlorotiazide use was reported to cause hyperkalemia and/or an increase in serum creatinine values to dialysis values in 2 of 92 hypertensive, proteinuric patients with chronic kidney disease1. Regarding our case, in patients who doesnt have chronic kidney failure but have another predisposition to hyperkalemia like hyporeninemic hypoaldosteronism due to long-term diabetes mellitus, blockade of AT1 receptors may cause significant hyponatremia and intractable hyperkalemia reaching life-threatening levels.
1. Rysava R, Tesar V, Merta M & for the Czech Group for the Study of Glomerulonephritis. Effect of telmisartan on blood pressure control and kidney function in hypertensive, proteinuric patients with chronic kidney disease. Clin Pharmacol 2005 10 207213.