Ifosfamide-Induced Partial Arginine Vasopressin Resistance Responsive to Vasopressin/Desmopressin and Amiloride.

This is a case of partial arginine vasopressin resistance following the sixth cycle of doxorubicin-ifosfamide-mesna therapy for recurrent spindle cell sarcoma of the thigh. Polyuria and symptomatic hypernatremia started by the second day of the two-day chemotherapy cycle. The diagnosis was confirmed with serum and urine chemistry testing showing urine hypo-osmolality (161 mOsm/kg) with polyuria (4.8 L urine output) in 24 hours, serum hyperosmolality (355 mOsm/kg), and an elevated baseline plasma copeptin of 82 pmol/L. Treatment with intravenous vasopressin followed by amiloride and supraphysiologic doses of oral desmopressin improved symptomatic hypernatremia.