title: Evaluation of clinical assays for measuring high-dose methotrexate in plasma.
abstract: 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).
authors.affiliation: Department of Clinical Pharmacology, Karolinska Hospital, Stockholm, Sweden. Freidoun_Albertioni@micforum.ki.se
authors.forename: F
authors.initials: F
authors.lastname: Albertioni
authors.forename: C
authors.initials: C
authors.lastname: Rask
authors.forename: S
authors.initials: S
authors.lastname: Eksborg
authors.forename: J H
authors.initials: JH
authors.lastname: Poulsen
authors.forename: B
authors.initials: B
authors.lastname: Pettersson
authors.forename: O
authors.initials: O
authors.lastname: Beck
authors.forename: H
authors.initials: H
authors.lastname: Schroeder
authors.forename: C
authors.initials: C
authors.lastname: Peterson
mesh_terms: D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid; D003429:Cross Reactions; D004305:Dose-Response Relationship, Drug; D005069:Evaluation Studies as Topic; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D007124:Immunoenzyme Techniques; D008727:Methotrexate / Q000097:blood* / Q000627:therapeutic use; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000097:blood* / Q000188:drug therapy; D015203:Reproducibility of Results
chemical_list: D008727:Methotrexate