Leucovorin is one of several active, chemically reduced derivatives of folic acid. It is useful as an antidote to drugs which act as folic acid antagonists.Also known as folinic acid, citrovorum factor, or 5-formyl-5, 6, 7, 8-tetrahydrofolic acid, this compound has the chemical designation of calcium n-[p-[[[(6rs)-2-amino-5-formyl 5, 6, 7, 8-tetrahydo-4-hydroxy-6 pteridinyl]methyl]amino]benzoyl]-l-glutamate (1:1). The structural formula of leucovorin calcium is