Clearance and recovery calculations in hemodialysis: application to plasma, red blood cells, and dialysate measurements for cyclophosphamide.

The hemodialyzability of cyclophosphamide was investigated in four patients on long-term hemodialysis. Cyclophosphamide 100 mg was given intravenously over 10 min before hemodialysis. Blood and dialysate samples were collected periodically during the 4 hr dialysis and measured by gas-liquid chromatography (GLC) for cyclophosphamide. Dialysis clearance calculated by arterial-venous difference and actual drug recovery in dialysate averaged 104 ml/min, which is in the range of the metabolic clearance of 95 ml/min for the drug. The extraction efficiency of the hollow-fiber dialyzers averaged 40% for plasma and red blood cell (RBC) samples. A mean of 37% of the administered dose of cyclophosphamide was removed during hemodialysis. The half-life (t 1/2) of the beta phase was 3.3 hr in our patients during hemodialysis, a 49% reduction of the 6.5 hr to t 1/2 reported in uremic patients. Because of the reduction in elimination t 1/2, larger dialysis clearance than metabolic clearance, high extraction efficiency, and significant drug removal during dialysis, we conclude that cyclophosphamide is dialyzable.