Methotrexate(MTX)可用於抗腫瘤和調節風濕免疫疾病。過去認為低劑量使用時較不易出現不良反應；然而根據國内藥品不良反應通報系統的資料顯示，仍有許多口服低劑量MTX所造成的藥品不良反應，其中血液和淋巴系統異常佔所有通報案例的三分之一，又以全血球減少症(pancytopenia)的人數最多。由於此藥具有經濟、方便、有效性，在臨床上有無可取代的地位。因此本文整合相關案例和文獻，對於使用低劑量MTX時所需注意的臨床事項，提出以下建議：初次使用此藥時需進行嚴格的病人評估並搭配使用測試劑量(test dose:5-10mg)，給藥後接近7天時需追蹤全血球數和肝腎功能，以福測早發性之特異體質過敏反應。當病人腎功能不良或具有危險因子時，應使用較低的測試劑量(test dose:2.5mg-5mg)。用藥後需定期追蹤血球數、肝腎功能和相關不良反應，並給予病人充分用藥衛教，以降低毒性的發生率。

Methotrexate is commonly used as a treatment for neoplasms and rheumatologic disorders. Low-dose oral usage was considered to be associated with lower risks of adverse events. Nevertheless, statistics from the Taiwan National Adverse Drug Reaction Reporting System report that MTX- related adverse effects (especially myelotoxicity) is increasing and deems that it’s a critical issue to deal with. This review thus focuses on precautions in use of low-dose MTX in clinical settings. Based on our review, for first-time users, it is suggested that MTX to be initiated at a test dose between 5- 10mg. Monitoring of laboratory tests at one week of initiating therapy, including complete blood count, liver function and renal function, are also recommended for first-time MTX users to detect early onset of idiosyncratic toxicity. For patients with impaired renal function or other risk factors for myelotoxicity, a test dose between 2.5- 5mg is recommended. Regular monitoring of laboratory tests and related side effects as well as patient education are also recommended to minimize the risk of MTX-induced toxicity.