RADIOIMMUNOASSAY FOR METHOTREXATE AND ITS COMPARISON WITH SPECTROFLUORIMETRIC PROCEDURES

Abstract

A radioimmunoassay procedure was developed for the direct measurement of methotrexate (MTX) in plasma, serum, CSF or urine samples. The assay is sensitive to levels of at least 100 pg of MTX and is highly specific for MTX in the presence of folinic acid (citrovorum factor), folic acid, tetrahydrofolic acid and other folate analogs and known metabolites. Results from this procedure were compared with those obtained with a spectrofluorimetric method, utilizing the plasma of cancer patients undergoing high dose MTX treatment with citrovorum factor rescue. Results indicate that the method should be useful in the future in assisting individualization of dosage regimens and in the study of the pharmacokinetics and metabolism of MTX in cancer patients.