Antidote for methotrexate toxicity:

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 (MTX)DHFA-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.