<prompt> Antidote for methotrexate toxicity:Folic acidFolinic acidVitamin BThymine  <response>: Ref: Katzung 14th ed. pg. 957; KDT, 6th ed. pg. 823 The toxicity of Mtx can not be overcome by folic acid, because it will not be converted to the active coenzyme form. However, folinic acid rapidly reverses the effect. Thymidine also counteracts the Mtx toxicity.METHOTREXATE MTXDHFA-DHFRaseTHFA Methotrexate is a highly efficacious antineoplastic drug which inhibits dihydrofolate reductase DHFRase enzyme- blocking the conversion of dihydrofolic acid DHFA to tetrahydrofolic acid THFA. This conversion is essential for formation of an essential coenzyme required for one carbon transfer reactions in denovo purine synthesis and amino acid interconversions. Methotrexate has cell cycle specific action kills cells in S phase; primarily inhibits DNA synthesis.Drug of choice for Mtx toxicity: FOLINIC ACID. 