Levoleucovorin

Folic acid is an essential B vitamin required by the body for the synthesis of purines, pyrimidines, and methionine before incorporation into DNA or protein. However, in order to function in this role, it must first be reduced by the enzyme dihydrofolate reductase (DHFR) into the cofactors dihydrofolate (DHF) and tetrahydrofolate (THF). This important pathway, which is required for de novo synthesis of nucleic acids and amino acids, is disrupted when high-dose methotrexate is used for cancer therapy. As methotrexate functions as a DHFR inhibitor to prevent DNA synthesis in rapidly dividing cells, it also prevents the formation of DHF and THF. This results in a deficiency of coenzymes and a resultant buildup of toxic substances that are responsible for numerous adverse side effects of methotrexate therapy. As levoleucovorin and leucovorin are analogs of tetrahydrofolate (THF), they are able to bypass DHFR reduction and act as a cellular replacement for the co-factor THF, thereby preventing these toxic side effects.