Severe life-threatening hyponatremia associated with an amlodipine, chlorthalidone, and telmisartan fixed-dose combination

Hyponatremia, defined as serum sodium <135 mmol/L, is one of the most frequent electrolyte disorders, often associated with thiazide diuretic therapy. Clinical manifestations range from mild fatigue to life-threatening neurological complications. We report a 55-year-old woman with hypertension and hypothyroidism who developed severe hyponatremia (serum sodium 100 mmol/L) while on a fixed-dose combination of telmisartan, chlorthalidone, and amlodipine. She presented with altered sensorium, vomiting, lethargy, and generalized weakness. Investigations confirmed severe hyponatremia with concurrent treatment. The fixed-dose combination was discontinued, and she was treated with hypertonic saline, potassium supplementation, and amlodipine as antihypertensive therapy, leading to normalization of sodium levels. She was discharged on the 5 th day of hospitalization with amlodipine continued as monotherapy. The adverse drug reaction was reported to the Indian Pharmacopoeia Commission. This case highlights the risk of critical hyponatremia with angiotensin receptor blocker–thiazide combinations, particularly chlorthalidone, and emphasizes the need for vigilant monitoring of electrolytes in patients receiving multidrug antihypertensive therapy.