- A form of folic acid used alone or with other drugs to treat certain types of colorectal cancer and anemia and to lessen the toxic effects of the anticancer drug methotrexate or other substances that block the action of folic acid. Leucovorin calcium is also being studied in the treatment of other conditions and types of cancer. It is a type of chemoprotective agent and a type of chemosensitizing agent. Leucovorin is the active ingredient of leucovorin calcium. Also called citrovorum factor and folinic acid.