- Courses 2, 4, and 6: Patients receive high-dose methotrexate (MTX) IV over 24 hours on day 1; cytarabine IV over 2 hours every 12 hours on days 2 and 3; and leucovorin calcium IV over 15 minutes every 6 hours for 8 doses beginning 12 hours after the last dose of each MTX infusion. Patients also receive denileukin diftitox IV over 60 minutes for 2 doses once MTX blood levels have cleared. Treatment repeats every 21 days for 3 courses in the absence of disease progression or unacceptable toxicity.