Text Box: STUDY OF THE BLOOD CONCENTRATION OF MTX IN THE TREATMENT OF CHILDREN LEUKEMIA Zhang Meihe Beijing Children’s Hospital, Beijing, China Objective: To investigate the pharmacokinetics of Metheorexae (MTX) in the treatment of children leukemia. Method: Two or three courses of treatment with MTX were given againist central nervous system leukemia in 26 children with leukemia. The dosage in each course of treatment was 3.0g/m2 body surface area. Fluorescence Polarization Immunoassay (FPIA) was used to monitor the blood concentration of MTX for six times in each course of treatment. Result: The peaks of blood concentration of MTX appeared at 24 hours after administration and returned to the beginning level at 48 hours.For 6 times the blood concentration of MTX reached toxic level.Among all the courses of treatment, 44 (70%) courses didn't show peak levels of MTX. Conclusion: Theraprutic drug monitoring (TDM) of MTX in treatment of children leukemia can direct clinical administration of MTX. The study indicates that proper shortening of intervals between administrations or increaing the dosage may provide more effective treatment for children leukemia. 1864