An S-phase specific antimetabolite antineoplastic agent, methotrexate competitively inhibits folic acid reductase, preventing the reduction of dihydrofolate to tetrahydrofolate and affecting production of purines and pyrimidines. Rapidly proliferating cells ( _e.g._, neoplasms, bone marrow, GI tract epithelium, fetal cells, etc.) are most sensitive to the drug’s effects. Dihydrofolate reductase has a much greater affinity for methotrexate than either folic acid or dihydrofolic acid and coadministration of folic acid will not reduce methotrexate’s effects. Leucovorin calcium, a derivative of tetrahydrofolic acid, can block the effects of methotrexate. Methotrexate also has immunosuppressive activity, possibly due to its effects on lymphocyte replication. Tumor cells have been noted to develop resistance to methotrexate that may be due to decreased cellular uptake of the drug.
Indicated for lymphomas and some solid tumors in dogs and cats (see the Doses section and the recommended treatment protocol references at the end of this section). In human medicine, methotrexate is also being used to treat refractory rheumatoid arthritis and severe psoriasis.
劑量數字暫停提供：VetPro 的劑量改依 DRUGAPI 藥物資料庫對外的內容，DRUGAPI 目前不提供可直接計算的劑量。下方列出 DRUGAPI 的審查結論與劑量審查引用的來源；計算機可手動輸入劑量換算。
確認原包裝、methotrexate 身分、鹽基、濃度、賦形劑、防腐劑、效期、完整性、法域與來源，排除 methoxyflurane 或鄰藥資料 由獸醫腫瘤專科確認物種、個體、診斷、證據層級、精確產品、途徑、單藥或複方方案及全部合併藥物 治療前逐案評估血球、感染與出血、肝腎、腸胃、肺、神經、皮膚、生殖、體液與照護者暴露風險，不套用人用閾值 由具危害藥物工程控制、個人防護、spill kit、污染清潔、排泄物、洗衣與廢棄物程序的受訓團隊製備與管理 疑似誤曝、排程錯誤或過量立即啟動獸醫腫瘤與毒物專業處置；leucovorin、glucarpidase、高劑量支持與藥物濃度只按專科個案契約
依出現頻率分組；嚴重副作用獨立列出，臨床上需立即辨識。
60%