Pharmacokinetics of cyclophosphamide in patients with systemic necrotizing angiitis

Summary— Cyclophosphamide pharmacokinetics were investigated following administration to patients with systemic necrotizing angiitis. Ten patients (eight women and two men) received cyclophosphamide as a 1-h-rate-constant intravenous infusion at doses ranging from 600 to 1200 mg. All patients received concomitant oral prednisone (1 mg/kg/d). Blood samples were collected at the end of drug infusion and 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 h later. Serum cyclophosphamide concentrations were assayed by high pressure liquid chromatography. The peak serum cyclophosphamide levels ranged from 15.7 to 29.4 mg/L. The mean cyclophosphamide elimination half-life was 6.2 ± 1.3 h (mean ± SD). The mean apparent volume of distribution and mean total plasma clearance were, respectively, 0.75 ± 0.22 L/kg (mean ± SD) and 83 ± 22 mL/min (mean ± SD). These results obtained in systemic vasculitic diseases were consistent with those observed in other studies with cancer patients receiving comparable doses of cyclophosphamide.