Methotrexate

Brand Names: Methotrexate

Drug Class: General Prescription

Overview

11 DESCRIPTION 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 C 20 H 22 N 8 O 5 and the molecular weight is 454.4 g/mol. The structural formula is: Methotrexate tablets, USP for oral use is available in bottles of 36 and 100 tablets. Each tablet contains 2.

Mechanism of Action

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/m 2 or less, the mean bioavailability is approximately 60%.

Indications

  • 1 INDICATIONS AND USAGE Methotrexate tablets are a diydrofolate reductase inhibitor indicated for the: • Treatment of adults and pediatric patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy maintenance regimen (1.1) • Treatment of adults with mycosis fungoides (1.1) • Treatment of adults with relapsed or refractory non-Hodgkin lymphoma as part of a metronomic combination regimen (1.1) • Treatment of adults with rheumatoid arthritis (1.2) • Treatment of pediatric patients with polyarticular juvenile idiopathic arthritis (pJIA) (1.

Common Doses

  • 20 mg
  • 75 mg
  • 10 mg
  • 2.5 mg

Dosage

2 DOSAGE AND ADMINISTRATION • Instruct patients and caregivers to take the recommended dosage as directed, because medication errors have led to deaths. (2.1, 5.9) • Verify pregnancy status in females of reproductive potential before starting methotrexate tablets. (4, 5.1) • ALL: The recommended dosage is 20 mg/m 2 orally once weekly as a part of a combination chemotherapy maintenance regimen. (2.2) • Mycosis fungoides: The recommended dosage is 25 to 75 mg orally once weekly as monotherapy; 10 mg/m 2 orally twice weekly as part of combination chemotherapy. (2.

Black Box Warning

WARNING: EMBRYO-FETAL TOXICITY, HYPERSENSITIVITY REACTIONS, and SEVERE ADVERSE REACTIONS • Methotrexate tablets can cause embryo-fetal toxicity, including fetal death. For non-neoplastic diseases, methotrexate tablets are contraindicated in pregnancy. For neoplastic diseases, advise females and males of reproductive potential to use effective contraception [see Contraindications (4), Warnings and Precautions (5.1), Use in Specific Populations (8.1, 8.3)].

Contraindications

  • 4 CONTRAINDICATIONS Methotrexate tablets are contraindicated in: • Pregnant women receiving methotrexate tablets for treatment of non-neoplastic diseases [see Warnings and Precautions (5.1), and Use in Specific Populations (8.1, 8.3)]. • Patients with a history of severe hypersensitivity reactions, including anaphylaxis, to methotrexate. [see Warnings and Precautions (5.2)]. • In pregnancy for non-neoplastic diseases (4) • History of severe hypersensitivity to methotrexate (4)

Side Effects

  • 6 ADVERSE REACTIONS The following clinically significant adverse reactions are described elsewhere in the labeling: Hypersensitivity Reactions [see Warnings and Precautions (5.2)] Myelosuppression [see Warnings and Precautions (5.3)] Gastrointestinal Toxicity [see Warnings and Precautions (5.4)] Hepatotoxicity [see Warnings and Precautions (5.5)] Pulmonary Toxicity [see Warnings and Precautions (5.6)] Dermatologic Reactions [see Warnings and Precautions (5.7)] Renal Toxicity [see Warnings and Precautions (5.8)] Serious Infections [see Warnings and Precautions (5.

Interactions

  • 7 DRUG INTERACTIONS Refer to the full prescribing information for drug interactions with methotrexate. (7) 7.1 Effects of Other Drugs on Methotrexate Drugs that Increase Methotrexate Exposure Coadministration of methotrexate with the following products may increase methotrexate plasma concentrations, which may increase the risk of methotrexate severe adverse reactions. In some cases, the coadministration of methotrexate with these products may also subsequently reduce active metabolite formation, which may decrease the clinical effectiveness of methotrexate.