Syndrome of Inappropriate Antidiuretic Hormone Secretion Induced by a Single Dose of Oral Cyclophosphamide

Cyclophosphamide was first synthe-sized over 50 years ago and is used extensively as a chemotherapeutic agent, both alone or in combination, in the treatment of numerous cancers, includ-ing breast, sarcoma, lymphoid, and pedi-atric malignancies.1 It is also widely used in bone marrow transplantation condi-tioning and mobilization regimens and for the treatment of various autoimmune disorders. Adverse effects include bone marrow suppression, cardiac and go-nadal toxicity, hemorrhagic cystitis, nau-sea and vomiting, alopecia, and carcino-genesis. Hyponatremia resulting from impaired excretion of water has been demonstrated in studies of patients re-ceiving cyclophosphamide in both high and low intravenous doses.2-5 Cyclophos-phamide-induced severe symptomatic hyponatremia commonly related to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) has been the subject of a number of English-lan-guage case reports since 1972.6-24 Pa-tients affected have ranged in age from 5 to 69 years, with 1 death being reported in a 5-year-old boy.7 Patients were re