About folinic acid (5-formyl tetrahydrofolate)5-formyl tetrahydrofolate generally administered as calcium or sodium folinate ,is an is one active form in a group of vitamins known as folates.mechanism of action of folinic acid (5-formyl tetrahydrofolate)folinic acid is a 5-formyl derivative of tetrahydrofolic acid. it is readily converted to other reduced folic acid derivatives (e.g., tetrahydrofolate), and, thus, has vitamin activity that is equivalent to that of folic acid. however, since it does not require the action of dihydrofolate reductase for its conversion, its function as a vitamin is unaffected by inhibition of this enzyme by drugs such as methotrexate. folinic acid, therefore, allows for some purine/pyrimidine synthesis to occur in the presence of dihydrofolate reductase inhibition, so that some normal dna replication and rna transcription processes can proceed.