Methotrexate (Page 5 of 7)

8.4 Pediatric Use

The safety and effectiveness of methotrexate tablets in pediatric patients have been established for the treatment of ALL as part of the combination chemotherapy maintenance regimen and the treatment of pJIA [see Indications and Usage (1), Dosage and Administration (2)]. No new safety signals have been observed in pediatric patients in clinical studies [see Adverse Reactions (6.1)].

The safety and effectiveness of methotrexate tablets have not been established in pediatric patients for the other indications [see Indications and Usage (1)].

8.5 Geriatric Use

Clinical studies of methotrexate did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects.

8.6 Renal Impairment

Methotrexate elimination is reduced in patients with renal impairment [see Clinical Pharmacology (12.3)]. Patients with renal impairment are at increased risk for methotrexate adverse reactions. Closely monitor patients with renal impairment [creatinine clearance (CLcr) less than 90 mL/min, Cockcroft-Gault] for adverse reactions. Reduce the dosage or discontinue methotrexate tablets as appropriate [see Warnings and Precautions (5.8)].

8.7 Hepatic Impairment

The pharmacokinetics and safety of methotrexate in patients with hepatic impairment is unknown. Patients with hepatic impairment may be at increased risk for methotrexate adverse reactions based on the elimination characteristics of methotrexate [see Clinical Pharmacology (12.3)]. Closely monitor patients with hepatic impairment for adverse reactions. Reduce the dosage or discontinue methotrexate tablets as appropriate [see Warnings and Precautions (5.5)].

10 OVERDOSAGE

Overdosage, including fatal overdosage, has occurred with methotrexate [see Warnings and Precautions (5. 9)].

Manifestations

Manifestations of methotrexate overdosage include adverse reactions reported at pharmacologic doses, particularly hematologic and gastrointestinal reactions (e.g., leukopenia, thrombocytopenia, anemia, pancytopenia, myelosuppression, mucositis, stomatitis, oral ulceration, nausea, vomiting, gastrointestinal ulceration, or gastrointestinal bleeding). In some cases, no symptoms were reported; however, sepsis or septic shock, renal failure, and aplastic anemia were also reported.

Management

Leucovorin and levoleucovorin are indicated for diminishing the methotrexate adverse reactions of methotrexate overdosage. Administer leucovorin or levoleucovorin as soon as possible after methotrexate overdosage). Monitor serum creatinine and methotrexate levels to guide leucovorin or levoleucovorin therapy. Refer to the leucovorin or levoleucovorin prescribing information for additional dosage information.

Glucarpidase is indicated for the treatment of toxic plasma methotrexate concentrations (>1 micromole per liter) in patients with delayed methotrexate clearance due to impaired renal function. Refer to the glucarpidase prescribing information for additional dosage information.

Administer concomitant hydration and urinary alkalinization.

Neither hemodialysis nor peritoneal dialysis has been shown to improve methotrexate elimination; however, methotrexate has been effectively cleared with acute, intermittent hemodialysis using a high-flux dialyzer.

11 DESCRIPTION

Methotrexate (formerly Amethopterin) is an antimetabolite used in the treatment of certain neoplastic diseases, severe psoriasis, and adult rheumatoid arthritis. Chemically methotrexate is N-[4-[[(2,4diamino-6-pteridinyl) methyl]methylamino]benzoyl]-L glutamic acid. The structural formula is:

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Molecular Formula : C20 H20 N8 O5 Na2

Molecular Weight : 498.40

Methotrexate sodium is orange, brownish, or yellow crystalline hygroscopic powder. It is freely soluble in water.

Methotrexate Tablets, USP contain an amount of methotrexate sodium equivalent to 2.5 mg of methotrexate and the following inactive ingredients: anhydrous lactose, lactose monohydrate, microcrystalline cellulose, magnesium stearate and pregelatinized starch.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Methotrexate inhibits dihydrofolic acid reductase. Dihydrofolates must be reduced to tetrahydrofolates by this enzyme before they can be utilized as carriers of one-carbon groups in the synthesis of purine nucleotides and thymidylate. Therefore, methotrexate interferes with DNA synthesis, repair, and cellular replication. Actively proliferating tissues such as malignant cells, bone marrow, fetal cells, buccal and intestinal mucosa, and cells of the urinary bladder are in general more sensitive to this effect of methotrexate.

The mechanism of action in rheumatoid arthritis and in psoriasis is unknown.

12.3 Pharmacokinetics

Absorption

At doses of 30 mg/m2 or less, the mean bioavailability is approximately 60%. Peak plasma concentrations are reached within 0.75 to 6 hours following oral administration. Methotrexate may undergo enterohepatic recirculation; however, this pathway has not been fully characterized.

Effect of Food

Food has been shown to delay absorption and reduce peak concentration.

Distribution

Methotrexate in serum is approximately 50% protein bound.

Methotrexate does not penetrate the blood-cerebrospinal fluid barrier at concentrations achieved with the recommended dosages.

Elimination

The elimination half-life of methotrexate is approximately 3 to 10 hours.

Small amounts of methotrexate polyglutamates may remain in tissues for extended periods. The retention and prolonged drug action of these active metabolites vary among different cells, tissues, and tumors.

Nonlinear elimination due to saturation of renal tubular reabsorption has been observed in studies of patients with psoriasis receiving methotrexate doses between 7.5 mg and 30 mg.

Metabolism

Methotrexate is partially metabolized by intestinal flora after oral administration.

Methotrexate primarily undergoes hepatic and intracellular metabolism to active polyglutamated forms which can be converted back to methotrexate by hydrolase enzymes. Methotrexate also undergoes minor metabolism to active 7-hydroxymethotrexate.

Excretion

Methotrexate primarily undergoes renal excretion by glomerular filtration and active tubular secretion that is dependent upon dosage and route of administration.

Biliary excretion accounts for ≤10% of the methotrexate dose.

Specific Populations

The effect of hepatic impairment on the pharmacokinetics of methotrexate is unknown.

Pediatric Patients

In pediatric patients with leukemia, oral absorption (23% to 95%) of methotrexate is variable and dose-dependent. The difference between highest and lowest peak methotrexate concentrations (Cmax 0.11 to 2.3 micromolar after a 20 mg/m2 dose) was 20-fold. The time to peak concentration (Tmax 0.67 to 4 hours after a 15 mg/m2 dose) and fraction of dose absorbed is variable. The absorption of doses greater than 40 mg/m2 is significantly less than that of lower doses.

In pediatric patients with pJIA, plasma concentrations of methotrexate are variable. Following oral administration of methotrexate 6.4 mg/m2 /week to 11.2 mg/m2 /week, mean serum concentrations were 0.59 micromolar (0.03 to 1.40) at 1 hour, 0.44 micromolar (0.01 to 1.00) at 2 hours, and 0.29 micromolar (0.06 to 0.58) at 3 hours.

In pediatric patients receiving methotrexate for acute lymphoblastic leukemia (6.3 mg/m2 to 30 mg/m2) or for JIA (3.75 mg/m2 to 26.2 mg/m2), the terminal half-life has been reported to range from 0.7 to 5.8 hours or from 0.9 to 2.3 hours, respectively.

Patients with Renal impairment

The elimination half-life of methotrexate is variable and increases with the severity of renal impairment.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Methotrexate has been evaluated in a number of animal studies for carcinogenic potential with inconclusive results. There is evidence that methotrexate causes chromosomal damage to animal somatic cells and human bone marrow cells.

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