Radioassay of chlorpromazine and its metabolites in plasma

Abstract

Conditions have been established for the quantitative formation of radiolabeled derivatives of chlorpromazine, chlorpromazine sulfoxide and their demethylated analogs in plasma extracts.

Tritiated N-acetyl derivatives are formed from the demethylated compounds and C¹⁴-quaternary amines from the tertiary amines by acetylation and methylation, respectively. These reactions are quantitative over a wide range of concentrations.

The reactions may be performed sequentially when chloropromazine and its Nor derivatives (or chlorpromazine sulfoxide and its Nor derivatives) exist in a single extract. Herein, the mixture is first acetylated and subsequently methylated. The labeled derivatives are quantitatively separated and recovered by selective solvent partition.

An extraction procedure has been suggested by which chlorpromazine and its Nors may be separated from chlorpromazine sulfoxide and its Nor derivatives so that each fraction may be subjected to the sequential acetylation and methylation reactions. Recoveries of μg quantities of standards from plasma are less than quantitative, probably because of losses due to glass adsorption and protein binding, but may be corrected with appropriate internal standards. As low as 15–20 ng/ml of each compound are measurable in a 3 ml plasma aliquot.

The method has been applied to a limited number in vivo experiments in dogs and in humans.