Possible Pentostatin‐Induced Symptomatic Hyponatremia

Pentostatin is an adenosine deaminase inhibitor used in the treatment of hairy cell leukemia and T‐cell lymphomas. A 27‐year‐old man with refractory cutaneous T‐cell lymphoma developed severe hyponatremia 3 days after completing his first cycle of pentostatin therapy. Shortly after hospital admission, he became disoriented and was admitted to the medical intensive care unit and treated with a combination of hypertonic saline, intravenous diuretics, and fluid restriction to reestablish normal sodium homeostasis. The mechanism by which pentostatin may have induced hyponatremia in this patient is unknown; clinical and laboratory findings represented both extrarenal sodium loss and syndrome of inappropriate antidiuretic hormone. Clinicians should be aware of the possible development of life‐threatening symptomatic hyponatremia in patients receiving pentostatin.