An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of TETRAHYDROFOLATE DEHYDROGENASE and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA.
Methotrexate is only found in individuals that have used or taken this drug. It is an antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of tetrahydrofolate dehydrogenase and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA. [PubChem]Methotrexate anti-tumor activity is a result of the inhibition of folic acid reductase, leading to inhibition of DNA synthesis and inhibition of cellular replication. The mechanism involved in its activity against rheumatoid arthritis is not known.
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- Metabolism: After absorption, methotrexate undergoes hepatic and intracellular metabolism to form methotrexate polyglutamate, metabolites which by hydrolysis may be converted back to methotrexate. Methotrexate polyglutamates inhibit dihydrofolate reductase and thymidylate synthetase. Small amounts of these polyglutamate metabolites may remain in tissues for extended periods; the retention and prolonged action of these active metabolites vary among different cells, tissues, and tumors. In addition, small amounts of methotrexate polyglutamate may be converted to 7-hydroxymethotrexate; accumulation of this metabolite may become substantial following administration of high doses of methotrexate, since the aqueous solubility of 7-hydroxymethotrexate is threefold to fivefold lower than that of the parent compound. Following oral administration of methotrexate, the drug also is partially metabolized by the intestinal flora. Renal excretion is the primary route of elimination, and is dependent upon dosage and route of administration (A620). Route of Elimination: Renal excretion is the primary route of elimination and is dependent upon dosage and route of administration. IV administration, 80% to 90% of the administered dose is excreted unchanged in the urine within 24 hours. There is limited biliary excretion amounting to 10% or less of the administered dose. Half Life: Low doses (less than 30 mg/m^2): 3 to 10 hours; High doses: 8 to 15 hours.
- Uses/Sources: Methotrexate is indicated in the treatment of gestational choriocarcinoma, chorioadenoma destruens and hydatidiform mole. In acute lymphocytic leukemia, methotrexate is indicated in the prophylaxis of meningeal leukemia and is used in maintenance therapy in combination with other chemotherapeutic agents. Methotrexate is also indicated in the treatment of meningeal leukemia. Methotrexate is used alone or in combination with other anticancer agents in the treatment of breast cancer, epidermoid cancers of the head and neck, advanced mycosis fungoides (cutaneous T cell lymphoma), and lung cancer, particularly squamous cell and small cell types. Methotrexate is also used in combination with other chemotherapeutic agents in the treatment of advanced stage non-Hodgkin's lymphomas. Methotrexate is indicated in the symptomatic control of severe, recalcitrant, disabling psoriasis. Methotrexate is indicated in the management of selected adults with severe, active rheumatoid arthritis (ACR criteria), or children with active polyarticular-course juvenile rheumatoid arthritis.
- Health Effects: A small percentage of patients develop hepatitis, and there is an increased risk of pulmonary fibrosis where dry cough can be an important sign. The higher doses of methotrexate often used in cancer chemotherapy can cause toxic effects to the rapidly-dividing cells of bone marrow and gastrointestinal mucosa. The resulting myelosuppression and mucositis are often prevented (termed Leucovorin "rescue"- as this is the folic acid based drug used) (L1079).
- Symptoms: Symptoms of overdose include bone marrow suppression and gastrointestinal toxicity.
- Treatment: Administer charcoal as a slurry. Consider gastric lavage after ingestion of a potentially life-threatening amount of poison if it can be performed soon after ingestion (generally within 1 hour). Protect airway by placement in Trendelenburg and left lateral decubitus position or by endotracheal intubation. Control any seizures first. Glucarpidase has been used intravenously in combination with thymidine and leucovorin to treat methotrexate toxicity. (T36)
- Route of Exposure: Inhalation (A314); dermal (A314); intravenous (A314) Oral absorption is dose dependent in adults and leukemic pediatric patients. In adults, peak serum levels are reached within one to two hours. At doses of 30 mg/m^2 or less, methotrexate is generally well absorbed with a mean bioavailability of 60%. At doses greater than 80 mg/m^2, the absorption of the doses is significantly less due to a saturation effect.
- Carcinogenicity: 3, not classifiable as to its carcinogenicity to humans. (L135)
- Toxicity: LD50: 43 mg/kg (Oral, Rat) (A308)