Non‐equilibrium Method for the Radioimmunoassay of Clozapine in the Presence of Metabolites
- 1 November 1977
- journal article
- research article
- Published by Wiley in European Journal of Biochemistry
- Vol. 80 (2), 603-609
- https://doi.org/10.1111/j.1432-1033.1977.tb11917.x
Abstract
Cross-reactions with metabolites are an ever-recurring problem encountered in the use of radioimmunoassay techniques to determine active compounds in biological material. Metabolites may interfere with the assay of the parent drug to a variable extent. Taking 8-chloro-11-(4-methyl-1-piperazinyl)-5H-dibenzo[b,e] [1,4]diazepine (clozapine) as an example, it was shown that the extent to which the antiserum produced interacts with the parent drug and the metabolites can be estimated by determining equilibrium constants and kinetics. It was advantageous to carry out the radioimmunoassay in disequilibrium, i.e., in order to differentiate metabolites from the parent drug, the sample was incubated with the antiserum for 10 min, after which the labeled antigen was added and the reaction mixture again incubated for a brief exactly timed interval. Cross-reactions did not occur in mixtures of clozapine and its N-demethyl and N-oxide metabolites in the proportions 1:1:2 over a range of concentration of 1.5-48 ng clozapine/100 .mu.l human plasma. Equilibrium constants measured with the clozapine goat antiserum were as follows: clozapine 1.2 .times. 108 M-1, the N-demethyl metabolite 4.6 .times. 107 M-1 and the N-oxide metabolite 3.7 .times. 107 M-1 (pH 7.5 and 20.degree. C).This publication has 12 references indexed in Scilit:
- ClozapineDrugs, 1990
- Kinetics of interactions between antibodies and haptensBiochemistry, 1975
- Principles of Competitive Binding Assays (Saturation Analyses). II. Sequential SaturationClinical Chemistry, 1974
- Use of Gelatin-Coated Charcoal in Digoxin ImmunoassayClinical Chemistry, 1973
- Mathematical theory of cross-reactive radioimmunoassay and ligand-binding systems at equilibriumAnalytical Biochemistry, 1972
- Mathematical Analysis of Kinetics of Radioligand Assays: Improved Sensitivity Obtained by Delayed Addition of Labeled LigandJournal of Clinical Endocrinology & Metabolism, 1971
- Observations on programs to estimate the parameters of enzyme kineticsFEBS Letters, 1969
- 11‐Amino‐5H‐dibenzo[b, e]‐1, 4‐diazepine. 10. Mitteilung über siebengliedrige HeterocyclenHelvetica Chimica Acta, 1967
- PROTEIN MEASUREMENT WITH THE FOLIN PHENOL REAGENTJournal of Biological Chemistry, 1951