Abstract: The patient was diagnosed with acute lymphoblastic leukemia (Bline highrisk) for more than 5 months,  and was hospitalized again for consolidation chemotherapy. According to the treatment plan,  the patient was treated with highdose methotrexate (HDMTX) 5 g/m2 for chemotherapy,  and the rescue drugcalcium folinate,  was used according to the first dose of MTX at 43 h (that is,  full 42 h). The dosage of calcium folinate was 15 mg/m2,  and plasma concentration of MTX at 48 h was 32 μmol/L. Considering the MTX poisoning,  the chemotherapy was suspended and the patient was rescued with large dose of calcium folinate according to MTX poisoning regimen,  and the treatment of fluid rehydration,  alkalization and forced diuresis was strengthened. At 72 h,  MTX plasma concentration was 16.9  μmol/L. The largedose calcium folinate was continuously given to the patient,  then hydration and alkalization still went on. The child's abdominal pain showed no signs of remission,  and continuous renal replacement therapy (CRRT) was conducted from the 82nd hour. The plasma concentration of MTX still reached 7.2  μmol / L at 96 h. Considering the poor efficacy of CRRT,  plasma exchange was carried out at 124 h after MTX,  followed by CRRT. At 120 h,  the MTX plasma concentration dropped to 3.8 μmol/L. On the 7th day (148 h) of the poisoning,  plasma exchange was carried out again to accelerate the detoxification. The plasma concentration of MTX dropped to 0.52  μmol/L at 192 h.

Key words: methotrexate, plasma concentration,  , renal replacement therapy (RRT),  , plasma exchange