現在位置 : RA > (類風濕性關節炎) Methotrexate for Rheumatoid Arthritis
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Methotrexate (MTX) (至善錠)
一種常用的風濕病用藥，效果較強，常用於類風濕性關節炎及乾癬性關節炎。副作用包括口腔潰瘍(可以併用葉酸改善)，腸胃不適，肝功能異常(少見)，肺功能異常(少見)，剛開始使用時病人需注意是否有胃口不佳或黃疸症狀，所以當剛開始使用時醫師會定期追蹤。但是長期使用尚稱安全，長期使用時醫師會定期抽血追蹤。 |
Methotrexate (MTX) tablets
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Methotrexate for Rheumatoid Arthritis
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N-acetyl cysteine (NAC) Interaction with Methotrexate
Methotrexate Replenish Depleted Nutrients - This medication may deplete this substance from the body or interfere with how it works; extra intake may help replenish it. Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells. 232 However, most scientific research does not support this supposition. A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research. 233 Vitamin C appears to increase the effectiveness of chemotherapy in animals 234 and with human breast cancer cells in test tube research. 235 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy. 236 A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but it clearly shows that antioxidants need not be avoided for fear that the actions of chemotherapy are interfered with.237 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research. A new formulation of selenium (Seleno-Kappacarrageenan) was found to reduce kidney damage and white blood cell–lowering effects of cisplatin in one human study. However, the level used in this study (4,000 mcg per day) is potentially toxic and should only be used under the supervision of a doctor.238 Glutathione, the main antioxidant found within cells, is frequently depleted in individuals on chemotherapy and/or radiation. Preliminary studies have found that intravenously injected glutathione may decrease some of the adverse effects of chemotherapy and radiation, such as diarrhoea.239 The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence. |
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Methotrexate for Rheumatoid Arthritis
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Methotrexate (MTX) (至善錠)
Methotrexate (abbreviated MTX and formerly known as amethopterin, is an antimetabolite and antifolate drug. It is used in treatment of cancer, autoimmune diseases, ectopic pregnancy, and for the induction of medical abortions. It acts by inhibiting the metabolism of folic acid. Methotrexate began to replace the more toxic antifolate aminopterin starting in the 1950s. The drug was developed by Yellapragada Subbarao. History Image shows open bottle of methotrexate drug - one of the first chemotherapeutic drugs used in the early 1950s. In 1947, a team of researchers led by Sidney Farber showed aminopterin, a chemical analogue of folic acid developed by Yellapragada Subbarao of Lederle, could induce remission in children with acute lymphoblastic leukemia. The development of folic acid analogues had been prompted by the discovery that the administration of folic acid worsened leukemia, and that a diet deficient in folic acid could, conversely, produce improvement; the mechanism of action behind these effects was still unknown at the time. Other analogues of folic acid were in development, and by 1950, methotrexate (then known as amethopterin) was being proposed as a treatment for leukemia. Animal studies published in 1956 showed the therapeutic index of methotrexate was better than that of aminopterin, and clinical use of aminopterin was thus abandoned in favor of methotrexate. In 1951, Jane C. Wright demonstrated the use of methotrexate in solid tumors, showing remission in breast cancer. Wright's group were the first to demonstrate use of the drug in solid tumors, as opposed to leukemias, which are a cancer of the marrow. Min Chiu Li et al then demonstrated complete remission in women with choriocarcinoma and chorioadenoma in 1956, and in 1960 Wright et al produced remissions in mycosis fungoides. The drug was then investigated as a treatment for many other cancers, alone or in combination with other drugs, and was studied for other, noncancer indications in the 1970s. In 1988, it was approved by the U.S. Food and Drug Administration (FDA) to treat rheumatoid arthritis. In 2011, Ben Venue Laboratories shut down their production of injectable preservative-free methotrexate, leading to a shortage of the form of the drug commonly used to treat childhood Acute lymphoblastic leukemia. Medical uses Chemotherapy Methotrexate was originally developed and continues to be used for chemotherapy either alone or in combination with other agents. It is effective for the treatment of a number of cancers including: breast, head and neck, leukemia, lymphoma, lung, osteosarcoma, bladder, and trophoblastic neoplasms. Autoimmune disorders It is used as a treatment for some autoimmune diseases, including rheumatoid arthritis, Juvenile dermatomyositis, psoriasis, psoriatic arthritis, lupus, sarcoidosis, Crohn's disease, and many forms of vasculitis. Although methotrexate was originally designed as a chemotherapy drug (in high doses), in low doses methotrexate is a generally safe and well tolerated drug in the treatment of certain autoimmune diseases. Because of its effectiveness, low-dose methotrexate is now first-line therapy for the treatment of rheumatoid arthritis. Though methotrexate for autoimmune diseases is taken in lower doses than it is for cancer, side effects such as hair loss, nausea, headaches, and skin pigmentation are still common. Though not everybody is responsive to treatment with methotrexate, multiple studies and reviews showed that the majority of patients receiving methotrexate for up to one year had less pain, functioned better, had fewer swollen and tender joints, and had less disease activity overall as reported by themselves and their doctors. X-rays also showed that the progress of the disease slowed or stopped in many patients receiving methotrexate. It has also been used for multiple sclerosis but is not approved by the Food and Drug Administration. |
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Abortion
Methotrexate is commonly used (generally in combination with misoprostol) to terminate pregnancies during the early stages (i.e., as an abortifacient). It is also used to treat ectopic pregnancies. Administration It can be taken orally or administered by injection (intramuscular, intravenous, subcutaneous, or intrathecal). Oral doses are taken weekly not daily. Routine monitoring of the complete blood count, liver function tests, and creatinine are recommended. Measurements of creatinine are recommended at least every 2 months. Toxicity There are no reports of toxicity following acute oral ingestions and most cases with severe effects are from dosing interval errors (dose administered daily instead of weekly). High-dose intravenous methotrexate chemotherapy with acute kidney failure can result in severe toxicity. Inadvertent intrathecal overdose can result in severe and life-threatening CNS toxicity. Single acute oral ingestion Ingestion of less than 500 mg methotrexate in adults, or less than 5 mg/kg methotrexate in children, is unlikely to cause toxicity. Repeat oral ingestion Oral methotrexate is most toxic when the dosing interval is decreased, most commonly as an error from weekly to daily, especially if weekly doses are taken for more than 3 consecutive days. Clinical presentation Systemic effects of methotrexate poisoning include: ● Gastrointestinal effects—dose-related nausea and vomiting; gastrointestinal epithelial damage with severe stomatitis, diarrhoea and gastrointestinal bleeding. Hepatotoxicity occurs in severe cases ● Bone marrow toxicity—myelosuppression is worst 7 to 14 days after onset of toxicity ● CNS toxicity (particularly with intrathecal overdose)—seizures, coma, chemical meningitis. Adverse effects The most common adverse effects include: ulcerative stomatitis, low white blood cell count and thus predisposition to infection, nausea, abdominal pain, fatigue, fever, dizziness, acute pneumonitis and rarely pulmonary fibrosis. Methotrexate is a highly teratogenic drug and categorized in pregnancy category X by the FDA. Women must not take the drug during pregnancy, if there is a risk of becoming pregnant, or if they are breastfeeding. To engage in any of these activities (after discontinuing the drug), women must wait until the end of a full ovulation cycle. Central nervous system reactions to methotrexate have been reported, especially when given via the intrathecal route which include myelopathies and leucoencephalopathies. It has a variety of cutaneous side effects, particularly when administered in high doses. Generally, the more "nonspecific" action a pharmacological substance has, the more possible side effects can be expected. Methotrexate has, like all cytotoxic substances, a broad array of possible adverse effects. Drug interactions Penicillins may decrease the elimination of methotrexate and thus increase the risk of toxicity. While they may be used together increased monitoring is recommended. Probenecid inhibits methotrexate excretion, which increases the risk of methotrexate toxicity. Additionally, methotrexate neurotoxicity—which may cause seizures—is known to be induced by phenobarbital and carbamazepine, which are antiepileptic drugs. Its effects can be reversed by folinic acid (leucovorin) in a process known as "leucovorin rescue." |
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Mechanism of action
Methotrexate is thought to affect cancer and rheumatoid arthritis by two different pathways. For cancer, methotrexate competitively inhibits dihydrofolate reductase (DHFR), an enzyme that participates in the tetrahydrofolate synthesis. The affinity of methotrexate for DHFR is about one thousand-fold that of folate. DHFR catalyses the conversion of dihydrofolate to the active tetrahydrofolate. Folic acid is needed for the de novo synthesis of the nucleoside thymidine, required for DNA synthesis. Also, folate is needed for purine base synthesis, so all purine synthesis will be inhibited. Methotrexate, therefore, inhibits the synthesis of DNA, RNA, thymidylates, and proteins. Methotrexate acts specifically during DNA and RNA synthesis, and thus it is cytotoxic during the S-phase of the cell cycle. It therefore has a greater toxic effect on rapidly dividing cells (such as malignant and myeloid cells, and gastrointestinal and oral mucosa), which replicate their DNA more frequently, and thus inhibits the growth and proliferation of these noncancerous cells, as well as causing the listed side effects. Facing a scarcity of dTMP, rapidly dividing cancerous cells undergo cell death via thymineless death. For the treatment of rheumatoid arthritis, inhibition of DHFR is not thought to be the main mechanism, but rather the inhibition of enzymes involved in purine metabolism, leading to accumulation of adenosine, or the inhibition of T cell activation and suppression of intercellular adhesion molecule expression by T cells. In these cases, patients should supplement their diets with folate. In its low-dose regimen methotrexate blocks the binding of interleukin 1 beta to the interleukin 1 receptor on target cells. Pharmacokinetics Methotrexate is a weak dicarboxylic acid with pKa 4.8 and 5.5, and thus it is mostly ionized at physiologic pH. Oral absorption is saturatable and thus dose-dependent, with doses less than 40 mg/m2 having 42% bioavailability and doses greater than 40 mg/m2 only 18%. Mean oral bioavailability is 33% (13-76% range), and there is no clear benefit to subdividing an oral dose. Mean intramuscular bioavailability is 76%. Methotrexate is metabolized by intestinal bacteria to the inactive metabolite 4-amino-4-deoxy-N-methylpteroic acid (DAMPA), which accounts for less than 5% loss of the oral dose. Factors that decrease absorption include food, oral nonabsorbable antibiotics (e.g. vancomycin, neomycin, and bacitracin), and more rapid transit through the gastrointestinal tract (GI) tract, such as diarrhea, while slower transit time in the GI tract from constipation will increase absorption. Methotrexate is also administered in the placenta accreta, inhibiting the blood circulation to the target site. |
