- CNS prophylaxis: When blood counts recover, patients with acute leukemia or chronic myelogenous leukemia in blastic crisis resume IT methotrexate once every 2 weeks for a total of 4 doses (including the dose given before the conditioning regimen) and leucovorin calcium IV or orally 4 hours after (each dose of methotrexate) and every 6 hours for a total of 8 doses.