cimetropium and mifentidine

The use of precursor ion and constant neutral loss scanning as a means of rapidly detecting drug metabolites is evaluated. Four clinically useful drugs, namely (i) cyclophosphamide, (ii) mifentidine, (iii) cimetropium bromide and (iv) haloperidol, were subjected to microsomal incubations to afford phase I metabolites. Aside from a minor clean-up procedure involving zinc sulfate precipitation of microsomal proteins and solid-phase extraction of metabolites using a Sep-pak C-18 cartridge, the mixtures were analysed directly by fast atom bombardment tandem mass spectrometry. It is demonstrated that such screening strategies are important in detecting novel metabolites. However, there are some problems associated with only using such methods, including (i) the possibility of not detecting metabolites that undergo unusual collision-induced dissociation fragmentation pathways, (ii) the non-detection of metabolites that have undergone metabolic change at unusual sites of reactivity, and (iii) production of artifacts derived from the parent drug by the primary ionization process. Examples are discussed that highlight both the strengths and weaknesses of such an approach.

Topics: Cyclophosphamide; Evaluation Studies as Topic; Haloperidol; Histamine H2 Antagonists; Imidazoles; Mass Spectrometry; Parasympatholytics; Pharmaceutical Preparations; Scopolamine Derivatives

A comparative study of the use of organic solvent extraction versus Sep-Pak C18 cartridges in the recovery and analysis of phase I (unconjugated) drug metabolites using mass spectrometry is presented. Standard mixtures of putative metabolites of the anticholinergic drug cimetropium bromide and the H2-antagonist mifentidine were purified from inactivated liver microsomal preparations using both methods, and subsequently the recovery of each compound was quantitated. In general, the percentage recovery and degree of purification were greater when using Sep-Pak C18 cartridges compared with organic solvent extraction. Even more efficient recovery was achieved when zinc sulphate precipitation of proteins in the liver microsomal mixtures was carried out prior to analysis. Also, the HPLC-grade solvents used in this study contained a variety of ultraviolet-inactive, hydrophobic components. This leads to problems of suppression in fast atom bombardment mass spectrometric analysis. Using Sep-Pak C18 cartridges directly prior to analysis by fast atom bombardment with single or tandem mass spectrometry leads to far superior mass spectral results compared with organic solvent extraction.

Topics: Androgen Antagonists; Animals; Chromatography, High Pressure Liquid; Cricetinae; Guinea Pigs; Imidazoles; Mass Spectrometry; Mesocricetus; Mice; Microsomes, Liver; Parasympatholytics; Rats; Rats, Inbred Strains; Scopolamine Derivatives