Abstract
The TDXR system based upon fluorescence polarization immunoassay was used for therapeutic drug monitoring of methotrexate in serum. This system was evaluated for utility as well as precision and a test-dose method for individual dosage regimen adjustments in high-dose methotrexate therapy.
A comparison of the TDX system to enzyme immunoassay (EMITR sytem), which has been used for methotrexate assay, was made on 93 specimens; as a result, excellent correlation, r=0.998. The day-to-day precision was established by 8 replicated analyses during 2 weeks, where coefficient of variation was 0.72 to 2.56% of the within-day precision, CVs was 0.61 to 2.69%.
A study was made to determine if test-dose bolus injection could be used to predict infusion plateau methotrexate concentration. Small nontoxic dose of methotrexate (50mg/ m2) was given to patients who were followed for 24 hr. and the pharmacokinetic data were used to dose modification of high-dose methotrexate infusion.
We used 2 methods of assuming linear kinetics, the pharmacokinetic parameter and total body methotrexate clearance derived from the test-dose data, which can be used to predict infusion plateau methotrexate concentration. We have good prediction from pharmacokinetic parameter of 2 compartment models. It is concluded that test-dose method can be a useful guide to allow appropriate dose modification of high-dose methotrexate therapy.
