A Method for the Measurement of total Drug Convertible to Cysteamine: Application to Pharmacokinetic Experiments with Ethiofos

摘要

An analytical method has been developed for the quantification of cysteamine (2-aminoethanethiol) in plasma. A reductive sample pretreatment is used to convert disulfide-bound cysteamine to the free thiol which is subsequently separated by HPLC and detected by electrochemical detection (LCEC). The method was developed to follow drug disposition after administration of ethiofos (WR-2721, S-2-(3-aminopropylamino) ethyl phosphorothioic acid) and WR-1065 (2-(3-aminopropylamino)ethanethiol). Standard calibration curves were linear over the range 0.01- to 25.0 /μg/mL (0.130-324 μM) and a minimum detectable quantity of 0.01 μg/mL was calculated at a signal-to-noise ratio of 3. Assay precision over the same range averaged 2% (coefficient of variation) and relative recovery, used as a measure of accuracy, was 100Z. Stability of cysteamine in plasma, relative to an internal standard (2-aminopropanethiol, WR-186) was good; stored samples were found to contain an average of 94.6 ± 10.4z of the original cysteamine concentration following 28 days at -75 °C.