Evaluation of clinical assays for measuring high-dose methotrexate in plasma

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 42; no. 1; pp. 39 - 44
• Main Authors: ALBERTIONI, F, RASK, C, EKSBORG, S, POULSEN, J. H, PETTERSSON, B, BECK, O, SCHROEDER, H, PETERSON, C
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for Clinical Chemistry 1996
• Subjects: Analysis; Biological and medical sciences; Child; Child, Preschool; Chromatography, High Pressure Liquid; Cross Reactions; Dose-Response Relationship, Drug; Evaluation Studies as Topic; Fluorescence Polarization Immunoassay; General pharmacology; Humans; Immunoenzyme Techniques; Medical sciences; Medicin och hälsovetenskap; Methotrexate - blood; Methotrexate - therapeutic use; Pharmacology. Drug treatments; Precursor Cell Lymphoblastic Leukemia-Lymphoma - blood; Precursor Cell Lymphoblastic Leukemia-Lymphoma - drug therapy; Reproducibility of Results; Antineoplastic agent; Human; Biological fluid; HPLC chromatography; Enzyme immunoassay; Comparative study; Quantitative analysis; Blood plasma
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/42.1.39

Four routine assays commonly used for monitoring plasma methotrexate (MTX) during high-dose therapy were validated by HPLC as the comparison method. MTX and its main metabolite, 7-hydroxymethotrexate (7-OHMTX), were analyzed by HPLC with postcolumn derivatization and fluorometric detection. About 200 clinical plasma samples from 13 children with acute lymphoblastic leukemia who received 5-8 g/m2 MTX as 24-h infusions were analyzed. The fraction of measured concentrations of MTX that were within 75-125% of the values obtained by HPLC were 64.5% for enzyme inhibition assay, 56.4% for fluorescence polarization immunoassay with polyclonal antibodies (FPIA1; Abbott), 58.9% for FPIA2 (with monoclonal antibodies; Abbott), and 46.4% for enzyme-multiplied immunoassay (Emit; Syva). All nonchromatographic procedures were subject to interferences from MTX plasma metabolites or endogenous substances. The interference from 7-OHMTX was, however, somewhat less pronounced for FPIA2 (monoclonal) than for FPIA1 (polyclonal).