<prompt> Leucovorin is used to decrease the toxicity ofMethotrexate6-MercaptopurineThio-TEPACytosine arabinoside  <response>: Ref: Katzung 10th887; KDT 6e 823 Toxicity of methotrexate can be reversed by the administration of 5-formyltetrahydrofolate leucovorin or citrovorum factor. Folic acid in the diet is in dihydrofolate form. It is ineffective in reversing methotrexate toxicity. 