Novel 125I-labeled nortriptyline derivatives and their use in liquid- phase or magnetizable solid-phase second-antibody radioimmunoassays

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 25; no. 12; pp. 1997 - 2002
• Main Authors: Kamel, RS, Landon, J, Smith, DS
• Format: Journal Article
• Language: English
• Published: England Am Assoc Clin Chem 01.12.1979
• Subjects: Amitriptyline - blood; Amitriptyline - therapeutic use; Cross Reactions; Fluoresceins; Histidine - analogs & derivatives; Humans; Hydrogen-Ion Concentration; Iodine Radioisotopes; Isotope Labeling; Magnetics; Nortriptyline - analogs & derivatives; Nortriptyline - blood; Radioimmunoassay - methods; Thiocyanates
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/25.12.1997

Nortriptyline derivatives prepared by reaction with fluorescein isothiocyanate or conjugation to N-acetyl-L-histidine were radioiodinated and the products purified with Sephadex LH-20 columns to obtain two novel nortriptyline radioligands. Antisera were raised in rabbits by immunization with nortriptyline conjugated to succinylated ovine albumin. By use of the iodinated fluorescein derivative we developed a liquid-phase second-antibody radioimmunoassay that gives results correlating closely (r = 0.98) with those by an established radioimmunoassay of similar specificity in the assay of apparent total amitriptyline and its metabolite nortriptyline in serum or plasma from patients being treated with these drugs. With the iodinated N-acetyl-L-histidine derivative we developed a magnetizable solid-phase second-antibody radioimmunoassay. The cross reactivities of amitriptyline and nortriptyline could be made equal by performing the assay at pH 9.0, which makes it possible to measure true total active drug concentrations in patients receiving amitriptyline.