- The intensification phase begins after the CNS therapy ends and lasts for 30 weeks. This phase is intended to further reduce the number of leukemia cells in the body and consists of cycles of chemotherapy repeated every three weeks with weekly shots of asparaginase. The drugs administered to both groups during this phase are: prednisone or dexamethasone, vincristine,6-mercaptopurine, methotrexate, E. coli asparaginase and cytarabine. Patients in the "High Risk" group will also receive doxorubicin and dexrazoxane.