LEUCOKAST-50 Injection LEUCOKAST-50 contains Leucovorin Calcium (also known as Calcium Folinate), a 5-formyl derivative of tetrahydrofolic acid. Leucovorin serves as a reduced folate coenzyme precursor that bypasses dihydrofolate reductase (DHFR), an enzyme inhibited by antifolate chemotherapeutic agents like methotrexate. By supplying tetrahydrofolate derivatives directly, leucovorin restores intracellular active reduced folate pools, enabling thymidylate and purine synthesis and effectively rescuing normal host tissues from methotrexate-induced hematologic and gastrointestinal toxicity. Additionally, leucovorin enhances the biochemical activity of 5-fluorouracil (5-FU) by forming a stable ternary complex with thymidylate synthase and 5-dUMP, resulting in sustained enzyme inhibition. LEUCOKAST-50 is indicated for high-dose methotrexate rescue therapy, treatment of accidental methotrexate overdose, potentiation of 5-fluorouracil in advanced colorectal cancer regimens, and megaloblastic anemia due to folate deficiency when oral therapy is not feasible.