Clinical pharmacology of cyclophosphamide.

stools were determined by liquid scintillation counting. Plasma and urine alkylating activity was measured by reaction with 4-(4-nitrobenzyl)pyridine. Protein binding of cyclophosphamide and plasma alkylating metabolites were deter mined by plasma ultrafiltration. Injected Cyclophosphamide distributed rapidly into 64% of body weight, and plasma Cyclophosphamide half-life in patients without prior drug exposure was 6.5 hr. Not more than 20% of injected Cyclophosphamide was excreted intact in urine at any dose level. Plasma alkylating metabolites were 56% bound to plasma proteins. After a 40-mg/kg dose, peak unbound alkylating activity averaged 13.3 mamÃ3les/mi, and in most patients at this dose alkylating activity in the plasma was measurable for 24 hr. Sixty-eight % of injected 14C label was excreted in