- Leucovorin will be given by vein, over 5 minutes, on the day after each methotrexate dose and then by mouth every 6 hours after that, until the study doctor believes that the methotrexate level in the blood is low. The methotrexate level in the blood will be checked using a blood test (less than 2 teaspoons each time). This test will be performed once a day after each methotrexate infusion, until the methotrexate blood level is low and it is considered safe to stop the leucovorin.