Cyclophosphamide and water retention: Mechanism revisited

We describe an 8 year-old girl with established diabetes insipidus who deve loped cyclophosphamide-associated antidiuresis, The patient had received cy clophosphamide as part of a high-dose chemotherapy regimen for recurrent su prasellar dysgerminoma prior to autologous bone marrow transplantation. Uri nary output decreased and specific gravity increased shortly after a 1 hour i.v. infusion of 50 mg/kg cyclophosphamide and the effect lasted some 5 ho urs. No other drug could be implicated. This response, occurring in a patie nt with no ability to secrete vasopressin, suggests a direct tubular effect of one or more cyclophosphamide metabolites. Administering i.v. cyclophosp hamide requires careful monitoring of fluid balance in order to avoid water intoxication. Further research is warranted both into the mechanism of thi s effect and the metabolite responsible for it.