List of products in the National Drug Code with proprietary name . This medication is used to treat or prevent serious blood cell disorders (such as thrombocytopenia, neutropenia, anemia) caused by certain drugs (folic acid antagonists such as methotrexate, trimethoprim, pyrimethamine). It may also be used with a certain cancer drug (5-fluorouracil) to treat patients with colon cancer. Leucovorin may also be used to treat a certain type of anemia (due to folic acid deficiency) when folic acid cannot be taken by mouth.