Syndrome of inappropriate secretion of antidiuretic hormone induced by tacrolimus hydrate

A 24-year-old man with chronic myelocytic leukemia underwent a bone marrow transplant. Tacrolimus hydrate (FK506) was given for the prophylaxis of graft versus host disease (GVHD), but subsequently grade II skin and intestinal GVHD occurred. Increased administration of FK506 with simultaneous use of prednisolone relieved GVHD; however, hyponatremia occurred. Because renal function was normal and urinary osmolality was higher than serum osmolality, syndrome of inappropriate secretion of antidiuretic hormone (SIADH) was diagnosed. When FK506 was replaced by cyclosporine on day 43, the hyponatremia improved rapidly. FK506 is thought to be the agent that caused SIADH in the present case