Deuterium-labelling and quantitative measurement of ketotifen in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry.

A gas chromatographic/mass spectrometric assay for the anti-anaphylactic agent Ketotifen is described. The method is based on negative ion chemical ionization, utilizing the electrophoric nature of the underivatized drug. A simple procedure for deuteration of the intact target molecule is presented, thus enhancing specificity by internal standardization via stable isotope dilution. The assay was applied to pharmacokinetics of the drug in man.