異位性妊娠（又稱子宮外孕），是指胚胎沒有正常的在子宮腔內著床發育。異位性妊娠的胚胎除了因為發育的位置不恰當，所以無法健康成長，同時繼續妊娠亦會引起母體的病變及傷害，甚至造成母體死亡，所以異位性妊娠通常會在醫師的建議下終止懷孕。本案例為29 歲異位性妊娠女性，由於人員將手寫醫令輸入電子醫令的失誤，誤將methotrexate (MTX) 50 mg IM 開立成1 mg。再次回診時發現醫令錯誤，經處置正確治療劑量後，經過四星期的追蹤，患者之血中β-hCG 數值已由6920 mIU/mL 降至67 mIU/mL，呈現持續下降，成功終止懷孕。
MTX一般臨床上多應用於癌症化學治療，當使用於妊娠婦女時，所有醫療人員更應謹慎注意使用劑量，不論是過高或過低的劑量，都有可能對異位性妊娠患者帶來危及生命之傷害。因此，本文將進一步探討此用藥疏失以預防類似情形在本院或他院再次發生。
 

An ectopic pregnancy occurs when a fertilized ovum implants outside the normal uterine cavity. It is a common cause of morbidity and occasionally of mortality in women of reproductive age. A case of 29-yearold women with ectopic pregnancy was treated with methotrexate (MTX) 1 mg IM. On her next return for following up in clinic, the mistake of dosage was found. MTX in single dose intramuscular regimen (50 mg)was given again and the serum β-hCG successfully declined to 67  IU/mL in four weeks. The pregnancy was successfully ceased.
MTX is a cytotoxic chemotherapy agent. The dosage should be extremely concerned for the safety when it is used in a patient with ectopic pregnancy. This case report discussed the medication error and the management of ectopic pregnancy.