title: Competitive protein binding assay for piritrexim.
abstract: A competitive protein binding assay for piritrexim (PTX, 1) that makes use of a commercially available radioassay kit for methotrexate has been developed. After it is selectively extracted from plasma, PTX competes with [125l]methotrexate for binding to dihydrofolate reductase isolated from Lactobacillus casei. Free drug is separated from bound drug by adsorption to dextran-coated charcoal. Piritrexim is measurable over a range of 0.01 to 10.0 micrograms/mL in plasma with a coefficient of variation less than 15%. The limit of sensitivity of the assay is approximately 2 ng/mL. An excellent correlation between this assay and a previously published HPLC method was found. published HPLC method was found.
authors.affiliation: Wellcome Research Laboratories, Research Triangle Park, NC 27709.
authors.forename: J L
authors.initials: JL
authors.lastname: Woolley
authors.forename: J L
authors.initials: JL
authors.lastname: Ringstad
authors.forename: C W
authors.initials: CW
authors.lastname: Sigel
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism*; D001667:Binding, Competitive; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D005493:Folic Acid Antagonists; D006801:Humans; D007457:Iodine Radioisotopes; D011485:Protein Binding; D011743:Pyrimidines / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D005493:Folic Acid Antagonists; D007457:Iodine Radioisotopes; D011743:Pyrimidines; C024530:piritrexim