LEVOLEUCOVORIN (Page 3 of 4)

6.3 Postmarketing Experience

Since adverse reactions from spontaneous reports are provided voluntarily from a population of uncertain size, it is not always possible to estimate reliably their frequency or establish a causal relationship to drug exposure. Spontaneously reported adverse reactions collected by the WHO Collaborating Center for International Drug Monitoring in Uppsala Sweden have yielded seven cases where levoleucovorin was administered with a regimen of methotrexate. The events were dyspnea, pruritus, rash, temperature change and rigors. For 217 adverse reactions (108 reports) where levoleucovorin was a suspected or interacting medication, there were 40 occurrences of “possible allergic reactions.”

In an analysis where calcium levoleucovorin injection was reported as the primary suspect drug and fluorouracil (FU) was reported as a concomitant medication, possible allergic reactions were reported among 47 cases (67 events).

7 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 children. It is not known whether folinic acid has the same effects.

However, both folic and folinic acids share some common metabolic pathways. Caution should be taken when taking folinic acid in combination with anticonvulsant drugs.

Preliminary human studies have shown that small quantities of systemically administered leucovorin enter the CSF, primarily as its major metabolite, 5-methyltetrahydrofolate (5-MTHFA). In humans, the CSF levels of 5-MTHFA remain 1 to 3 orders of magnitude lower than the usual methotrexate concentrations following intrathecal administration. Levoleucovorin injection increases the toxicity of 5-fluorouracil [see Warnings and Precautions (5.2)].

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Pregnancy Category C. Animal reproduction studies have not been conducted with levoleucovorin injection. It is not known whether levoleucovorin injection can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Levoleucovorin injection should be given to a pregnant woman only if clearly needed.

8.3 Nursing Mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, and because of the potential for serious adverse reactions in nursing infants from levoleucovorin injection, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.

8.4 Pediatric Use

[See Clinical Studies (14)]

8.5 Geriatric Use

Clinical studies of levoleucovorin injection in the treatment of osteosarcoma did not include subjects aged 65 and over to determine whether they respond differently from younger subjects.

In the NCCTG clinical trial of levoleucovorin injection in combination with 5-FU in advanced colorectal cancer, adverse reactions were consistent with 5-FU related toxicity and were similar for patients age 65 and older and for patients younger than age 65.

10 OVERDOSAGE

No data are available for overdosage with levoleucovorin.

11 DESCRIPTION

Levoleucovorin is the levo isomeric form of racemic d,l-leucovorin, present as the calcium salt. Levoleucovorin is the pharmacologically active isomer of leucovorin [(6-S)-leucovorin].

Levoleucovorin Injection contain levoleucovorin calcium, which is one of several active, chemically reduced derivatives of folic acid. It is useful as antidote to the inhibition of dihydrofolate reductase by methotrexate. This compound has the chemical designation calcium (6S)-N-{4-[[(2-amino-5-formyl-1,4,5,6,7,8-hexahydro-4-oxo-6pteridinyl)methyl] amino]benzoyl}-L-glutamate pentahydrate. The molecular weight is 601.6 and the structural formula is:

structure
(click image for full-size original)

Its molecular formula is: C20 H21 CaN7 O7 . 5 H2 O

Levoleucovorin Injection is supplied as a sterile solution of either 175 mg levoleucovorin in 17.5 mL or 250 mg levoleucovorin in 25 mL. Each mL contains levoleucovorin calcium pentahydrate equivalent to 10 mg levoleucovorin and 8.3 mg sodium chloride. Sodium hydroxide is used for pH adjustment to pH 8.0 (6.5 to 8.5).

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

12.1.1 Levoleucovorin effects during high-dose methotrexate therapy Levoleucovorin is the pharmacologically active isomer of 5-formyl tetrahydrofolic acid. Levoleucovorin does not require reduction by the enzyme dihydrofolate reductase in order to participate in reactions utilizing folates as a source of “onecarbon” moieties. Administration of levoleucovorin can counteract the therapeutic and toxic effects of folic acid antagonists such as methotrexate, which act by inhibiting dihydrofolate reductase.

12.1.2 Levoleucovorin effects in combination with 5-fluorouracil Levoleucovorin can enhance the therapeutic and toxic effects of fluoropyrimidines used in cancer therapy such as 5-fluorouracil. 5-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 readily converted to another reduced folate, 5,10-methylenetetrahydrofolate, which acts to stabilize the binding of FdUMP to thymidylate synthase and thereby enhances the inhibition of this enzyme.

12.2 Pharmacodynamics

Levoleucovorin is actively and passively transported across cell membranes. In vivo, levoleucovorin is converted to 5-methyltetrahydrofolic acid (5-methyl-THF), the primary circulating form of active reduced folate. Levoleucovorin and 5-methyl-THF are polyglutamated intracellularly by the enzyme folylpolyglutamate synthetase. Folylpolyglutamates are active and participate in biochemical pathways that require reduced folate.

12.3 Pharmacokinetics

The pharmacokinetics of levoleucovorin after intravenous administration of a 15 mg dose was studied in healthy male volunteers. After rapid intravenous administration, serum total tetrahydrofolate (total-THF) concentrations reached a mean peak of 1722 ng/mL. Serum (6S)-5-methyl-5,6,7,8-tetrahydrofolate concentrations reached a mean peak of 275 ng/mL and the mean time to peak was 0.9 hours. The mean terminal half-life for total-THF and (6S)-5-methyl-5,6,7,8 tetrahydrofolate was 5.1 and 6.8 hours, respectively.

A pharmacokinetic study was conducted in 40 healthy subjects who received a single intravenous dose of either levoleucovorin (200 mg/m2) or racemic d,l-leucovorin (400 mg/m2), each administered as a 2-hour infusion in a crossover design. Results indicate that the 90% confidence interval for the geometric mean ratios for both AUC0-inf and Cmax were within the standard limit of 80 to 125% for both l-leucovorin and l-5-methyl-THF. Therefore, the exposure to l-leucovorin and 5-methyl-THF (AUC0-inf and Cmax ) was comparable whether it was administered as levoleucovorin or as d,l-leucovorin. The geometric mean AUC0-inf values for levoleucovorin were 30719 ng.h/mL and 31296 ng.h/mL for levoleucovorin and d,l-leucovorin, respectively. The geometric mean Cmax values for levoleucovorin were 10895 ng/mL and 11301 ng/ mL for levoleucovorin and d,l-leucovorin, respectively. The geometric mean AUC0-inf values for 5-methyl-THF were 52105 ng.h/mL and 50137 ng.h/mL for levoleucovorin and d,l-leucovorin, respectively. The geometric mean Cmax values for 5-methyl-THF were 4930 ng/mL and 4658 ng/mL for levoleucovorin and d,l-leucovorin, respectively.

Use of Levoleucovorin in combination with 5-fluorouracil A published cross study comparison showed that the mean dose-normalized steady-state plasma concentrations for both levoleucovorin and 5-methyl-THF were comparable whether 5-FU (370 mg/m2 /day IV bolus) was given in combination with levoleucovorin (250 mg/m2 and 1000 mg/m2 as a continuous IV infusion for 5.5 days, N=9) or in combination with d,l-leucovorin (500 mg/m2 as a continuous IV infusion for 5.5 days, N=6).

13 NONCLINICAL TOXICOLOGY

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