- Intensive continuation (weeks 25-80): At weeks 25-72 for arms I and II, and at weeks 33-80 for arms III and IV, patients receive oral MTX every 6 hours for 4 doses on weeks 1, 3, 5, 7, 9, and 11; oral mercaptopurine daily; oral leucovorin calcium every 12 hours for 2 doses beginning 48 hours after the start of MTX; IT MTX and vincristine IV on day 1 of week 12; and oral dexamethasone twice daily on days 1-7, beginning with the administration of vincristine. Treatment repeats every 12 weeks for 4 courses.