- Arm II (high-dose MTX): Patients receive vincristine IV and high-dose methotrexate IV over 24 hours on days 1, 15, 29, and 43; oral MP on days 1-56; and IT MTX on days 1 and 29. Patients also receive leucovorin calcium IV every 6 hours for at least 3 doses, beginning 42 hours after start of each MTX infusion.