Overview
DESCRIPTION Leucovorin is one of several active, chemically reduced derivatives of folic acid. It is useful as an antidote to drugs which act as folic acid antagonists. Also known as folinic acid, Citrovorum factor, or 5-formyl-5,6,7,8-tetrahydrofolic acid, this compound has the chemical designation of Calcium N -[p-[[[(6 RS...
Mechanism of Action
CLINICAL PHARMACOLOGY Leucovorin is a mixture of the diastereoisomers of the 5-formyl derivative of tetrahydrofolic acid (THF). The biologically active compound of the mixture is the (-)- l -isomer, known as Citrovorum factor or (-)-folinic acid. Leucovorin does not require reduction by the enzyme dihydrofolate reductase in order to participate in reactions utilizing folates as a source of “one-carbon” moieties. l -Leucovorin ( l -5-formyltetrahydrofolate) is rapidly metabolized (via 5, 10-methenyltetrahydrofolate then 5, 10-methylenetetrahydrofolate) to l ,5-methyltetrahydrofolate.
Indications
- INDICATIONS AND USAGE Leucovorin calcium rescue is indicated after high dose methotrexate therapy in osteosarcoma. Leucovorin calcium is also indicated to diminish the toxicity and counteract the effects of impaired methotrexate elimination and of inadvertent over dosages of folic acid antagonists. Leucovorin calcium is indicated in the treatment of megaloblastic anemias due to folic acid deficiency when oral therapy is not feasible.
Common Doses
- 200 mg
- 370 mg
- 20 mg
- 425 mg
Dosage
DOSAGE AND ADMINISTRATION Advanced Colorectal Cancer Either of the following two regimens is recommended: 1. Leucovorin is administered at 200 mg/m 2 by slow intravenous injection over a minimum of 3 minutes, followed by 5-fluorouracil at 370 mg/m 2 by intravenous injection. 2. Leucovorin is administered at 20 mg/m 2 by intravenous injection followed by 5-fluorouracil at 425 mg/m 2 by intravenous injection. 5-Fluorouracil and leucovorin should be administered separately to avoid the formation of a precipitate. Treatment is repeated daily for five days.
Contraindications
- CONTRAINDICATIONS Leucovorin is improper therapy for pernicious anemia and other megaloblastic anemias secondary to the lack of vitamin B 12 . A hematologic remission may occur while neurologic manifestations continue to progress.
Side Effects
- ADVERSE REACTIONS Allergic sensitization, including anaphylactoid reactions and urticaria, has been reported following the administration of both oral and parenteral leucovorin. No other adverse reactions have been attributed to the use of leucovorin per se . The following table summarizes significant adverse events occurring in 316 patients treated with the leucovorin/5-fluorouracil combinations compared against 70 patients treated with 5-fluorouracil alone for advanced colorectal carcinoma.
Interactions
- Drug Interactions Folic acid in large amounts may counteract the antiepileptic effect of phenobarbital, phenytoin and primidone, and increase the frequency of seizures in susceptible pediatric patients. Preliminary animal and human studies have shown that small quantities of systemically administered leucovorin enter the CSF primarily as 5-methyltetrahydrofolate and, in humans, remain 1 to 3 orders of magnitude lower than the usual methotrexate concentrations following intrathecal administration.