Use of stable isotopes in the elucidation of drug biotransformation processes.

This article surveys the role of stable isotope labelling and mass spectrometric detection in the recognition and characterization of drug metabolites. Applications of the so-called isotope cluster technique, useful for both recognition of drug-related compounds and elucidation of their structures, are presented. The use of deuterium-labelled g.l.c./mass spectrometric derivatization reagents to facilitate the determination of drug metabolite structures via 'peak shifts' is illustrated.