摘要Tacrolimus(TAC)is increasingly used for immunosuppression in organ transplantation,dermatomyositis/polymyositis,and myasthenia gravis(MG)patients.[1]TAC has a narrow therapeutic window with overexposure leading to acute and chronic forms of adverse reactions(ADRs).After oral administration,TAC is predominantly absorbed in the duodenum and jejunum and has highly variable pharmacokinetics,particularly when diarrhea occurs.[2,3]Few data has been published on TAC overexposure following mild diarrhea.Mild diarrhea is relatively common and often unreported,which can easily be overlooked by physicians,especially in the emergency department.Here,we report the occurrence of serious ADRs to TAC after mild diarrhea in a MG patient with community-acquired pneumonia(CAP),including nephrotoxicity,metabolic abnormalities and severe immunosuppression.