Competitive protein binding assay for piritrexim

• Published in: Journal of pharmaceutical sciences Vol. 78; no. 9; p. 749
• Main Authors: Woolley, Jr, J L, Ringstad, J L, Sigel, C W
• Format: Journal Article
• Language: English
• Published: United States 01-09-1989
• Subjects: Antineoplastic Agents - metabolism; Binding, Competitive; Chromatography, High Pressure Liquid; Chromatography, Thin Layer; Folic Acid Antagonists; Humans; Iodine Radioisotopes; Protein Binding; Pyrimidines - metabolism
• ISSN: 0022-3549
• DOI: 10.1002/jps.2600780910

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.