Cyclophosphamide and the kidney

The effect of cyclophosphamide on renal function was studied in 17 normally hydrated patients with cancer. No nephrotoxic effects were observed. High‐dose cyclophosphamide (⩾50 mg/kg body weight) did, however, impair water excretion as manifested by weight gain, hyponatremia, and inappropriately concentrated urine. The decrease in serum osmolarity (range 6‐41mOsm/L) and increase in urine osmolarity (range 305–798 mOsm/L) occurred 4–12 hours after cyclophosphamide administration, lasted 20–24 hours, and correlated temporally with the urinary excretion of cyclophosphamide alkylating metabolites. In three patients who demonstrated the water retention syndrome plasma vasopressin concentration was determined; in only one could the rise in urine osmolarity be explained by a concomitant increase in circulating vasopressin levels. No change in creatinine clearance or urinary excretion of protein, sodium, potassium, calcium, phosphorus, uric acid, and amino acids was observed after cyclophosphamide. Two patients (9%) developed hemorrhagic cystitis; no other abnormalities of urine sediment occurred.