Source: FDA, National Drug Code (US) Revision Year: 2020
Levoleucovorin is the pharmacologically active isomer of 5-formyl tetrahydrofolic acid. Levoleucovorin does not require reduction by dihydrofolate reductase to participate in reactions utilizing folates as a source of “one-carbon” moieties. Administration of levoleucovorin counteracts the therapeutic and toxic effects of folic acid antagonists such as methotrexate, which act by inhibiting dihydrofolate reductase.
Levoleucovorin enhances the therapeutic and toxic effects of fluorouracil. Fluorouracil is metabolized to 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP), which binds to and inhibits thymidylate synthase (an enzyme important in DNA repair and replication). Levoleucovorin is converted to another reduced folate, 5,10-methylenetetrahydrofolate, which then acts to stabilize the binding of FdUMP to thymidylate synthase, thereby enhancing the inhibition of thymidylate synthase.
The pharmacokinetics of levoleucovorin after intravenous injection of a 15 mg dose was studied in healthy subjects. The mean maximum serum total tetrahydrofolate (total-THF) concentration was 1722 ng/mL (CV 39%) and the mean maximum serum (6S)-5-methyl-5,6,7,8-tetrahydrofolate concentration was 275 ng/mL (CV 18%) observed around 0.9 hours post injection.
Exploratory studies show that small quantities of systemically administered leucovorin enter the cerebrospinal fluid (CSF), primarily as its major metabolite 5-methyltetrahydrofolate (5-MTHFA). In humans, the CSF levels of 5-MTHFA remain 1-3 orders of magnitude lower than the usual methotrexate concentrations following intrathecal administration.
The mean terminal half-life was 5.1 hours for total-THF and 6.8 hours for (6S)-5-methyl-5,6,7,8-tetrahydrofolate.
The mean dose-normalized steady-state plasma concentrations for both levoleucovorin and 5-methyl-THF were comparable whether fluorouracil (370 mg/m2/day as an intravenous bolus) was given in combination with levoleucovorin (250 mg/m2 and 1000 mg/m2 as a continuous intravenous infusion for 5.5 days) or in combination with d,l-leucovorin (500 mg/m2 as a continuous intravenous infusion for 5.5 days).
No studies have been conducted to evaluate the potential of levoleucovorin for carcinogenesis, mutagenesis and impairment of fertility.
The efficacy of levoleucovorin rescue following high-dose methotrexate were evaluated in 16 patients aged 6 to 21 years, who received 58 courses of therapy for osteogenic sarcoma. High-dose methotrexate was one component of several different combination chemotherapy regimens evaluated across several trials. Methotrexate 12 g/m2 as an intravenous infusion over 4 hours was administered to 13 patients, who received levoleucovorin 7.5 mg every 6 hours for 60 hours or longer beginning 24 hours after completion of methotrexate. Three patients received methotrexate 12.5 g/m2 intravenously over 6 hours, followed by levoleucovorin 7.5 mg by intravenous infusion every 3 hours for 18 doses beginning 12 hours after completion of methotrexate. The mean number of levoleucovorin doses per course was 18.2 and the mean total dose per course was 350 mg. The efficacy of levoleucovorin rescue following high-dose methotrexate was based on adverse reaction profile [see Adverse Reactions (6.1)].
In a randomized clinical study conducted by the Mayo Clinic and the North Central Cancer Treatment Group (NCCTG) in patients with metastatic colorectal cancer comparing d,l leucovorin 200 mg/m2 and fluorouracil 370 mg/m2 versus leucovorin 20 mg/m2 and fluorouracil 425 mg/m2 versus fluorouracil 500 mg/m2, with all drugs administered by intravenous infusion daily for 5 days every 28 to 35 days, response rates were 26% (p=0.04 versus fluorouracil alone), 43% (p=0.001 versus fluorouracil alone), and 10%, respectively. Respective median survival times were 12.2 months (p=0.037), 12 months (p=0.050), and 7.7 months. The low dose d,l-leucovorin regimen was associated with a statistically significant improvement in weight gain of more than 5%, relief of symptoms, and improvement in performance status. The high dose d,l-leucovorin regimen was associated with a statistically significant improvement in performance status and trended toward improvement in weight gain and in relief of symptoms but these were not statistically significant.
In a second randomized clinical study conducted by Mayo and NCCTG, the fluorouracil alone arm was replaced by sequentially administered methotrexate, fluorouracil, and d,l leucovorin . Response rates with d,l leucovorin 200 mg/m2 and fluorouracil 370 mg/m2 versus d,l leucovorin 20 mg/m2 and fluorouracil 425 mg/m2 versus sequential methotrexate and fluorouracil and d,l leucovorin were 31% (p≤0.01), 42% (p≤0.01), and 14%, respectively. Respective median survival times were 12.7 months (p≤0.04), 12.7 months (p≤0.01), and 8.4 months. There was no statistically significant difference in weight gain of more than 5% or in improvement in performance status between the treatment arms.
A randomized controlled study conducted by the NCCTG in patients with metastatic colorectal cancer failed to show superiority of a regimen of fluorouracil + levoleucovorin to fluorouracil + d,l-leucovorin in overall survival. Patients were randomized to fluorouracil 370 mg/m2 intravenously and levoleucovorin 100 mg/m 2 intravenously, both daily for 5 days, or to fluorouracil 370 mg/m 2 intravenously and d,l-leucovorin 200 mg/m2 intravenously, both daily for 5 days. Treatment was repeated week 4 and week 8, then every 5 weeks until disease progression or unacceptable toxicity.
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