Leucovorin is the active form of the B complex vitamin, folate. Leucovorin is used as an antidote to drugs that decrease levels of folic acid.
Folic acid helps red and white blood cell formulation and the synthesis of hemoglobin.
Some treatments require what is called leucovorin rescue, because the drug used to treat the cancer or other infection has had an adverse effect on folic acid levels. Leucovorin is also taken to decrease the bone marrow toxicity of sulfa drugs, and in combination with pyrimethamine to decrease the toxicity of toxoplasmosis treatment. Leucovorin is used in combination with trimetrexate to prevent bone marrow toxicity. Leucovorin is also used in combination with chemotherapy such as methotrexate . Side effects Allergic sensitization reactions such as skin rash and itching have been reported in both oral and injected treatments.