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)].
Clinical studies of methotrexate did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects.
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)].
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)].
Overdosage, including fatal overdosage, has occurred with methotrexate [see Warnings and Precautions (5.9)].
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.
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.
Methotrexate, USP is dihydrofolate reductase inhibitor with the chemical name of N-[4-[[(2,4 diamino-6-pteridinyl) methyl]methylamino]benzoyl]-L glutamic acid. The molecular formula is C20 H22 N8 O5 and the molecular weight is 454.4 g/mol. The structural formula is:
Methotrexate tablets, USP for oral use are available in bottles of 36 and 100 tablets. Each methotrexate tablet, USP contains 2.5 mg methotrexate, USP equivalent to 2.74 mg methotrexate disodium and the following inactive ingredients: lactose monohydrate, magnesium stearate and maize starch.
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.
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.
Methotrexate in serum is approximately 50% protein bound. Methotrexate does not penetrate the blood-cerebrospinal fluid barrier at concentrations achieved with the recommended dosages.
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.
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.
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.
The effect of hepatic impairment on the pharmacokinetics of methotrexate is unknown.
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.
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