Abstract
Cyclophosphamide is commonly used in the treatment of malignant diseases. Symptomatic severe hyponatremia induced by low-dose cyclophosphamide is very uncommon worldwide. Recently we experienced a case of a 56-year-old woman with breast cancer who developed severe hyponatremia with generalized seizure after the first cycle of adjuvant chemotherapy with doxorubicin and cyclophosphamide. Her laboratory test showed a serum sodium of 116 mmol/L. Her hyponatremia was initially treated with hypertonic saline solution and furosemide. She completely recovered without neurological deficits after slow correction of the serum sodium concentration over two days. Clinicians must always keep in mind that life-threatening acute hyponatremia can be induced by intravenous cyclophosphamide during chemotherapy, even if the dosage is low.