<prompt> The form of THF used in treatment is :N5 formyl THFN5 methyl THFN10 formyl THFN5 formimino THF  <response>: N5 Formyl THFA Folinic acid has high stability so it is used therapeutically. Extra reading : N5 Formyl THFA Folinic Acid 5-formyl tetrahydrofolic acid or leucovorin is necessary co-factor in the body an essential B vitamin. Commercially available leucovorin is composed of a 1:1 racemic mixture of the dextrorotary and levorotary isomers, while levoleucovorin contains only the pharmacologically active levo-isomer. Uses : 1. to counteract the toxic effects of folic acid antagonists, such as methotrexate inhibits DHFR 2. in the treatment of megaloblastic anemias due to folic acid deficiency 