- Arm I (weeks 5-24): Patients receive IT methotrexate (MTX) on day 1 followed by MTX IV over 20 minutes followed by MTX continuously over 23.6 hours on weeks 7, 10, 13, 16,19, and 22. At 42 hours after the beginning of the MTX infusion, patients receive oral leucovorin calcium every 6 hours for a total of 3 doses. Patients also receive oral mercaptopurine daily beginning on week 5 and continuing until the completion of consolidation therapy; oral dexamethasone twice daily on days 1-7 of weeks 8 and 17; and vincristine IV on day 1 of weeks 8, 9, 17, and 18.