Bioanalytical applications of tandem mass spectrometry in the in vitro metabolism of the anticholinergic drug cimetropium bromide to detect differences in species metabolism

1. In vitro metabolism of the anticholinergic drug, cimetropium bromide, was investigated using four different animal hepatic microsomal incubates derived from rat, hamster, guinea pig, and mouse livers. 2. Constant neutral loss (CNL) tandem mass spectrometry was used to detect the presence of the N-methylenecyclopropyl-scopine functionality by monitoring loss of 54 daltons (corresponding to loss of methylenecyclopropane) in microsomal incubates. 3. A CNL loss of 46 daltons was used to screen for the presence of ester hydrolysis products. 4. A comparison of the daughter ion spectra obtained on ions detected by CNL scanning, with daughter ion spectra of synthetic standards, determined the presence of ten metabolites of cimetropium bromide. 5. Hydroxylation of the aromatic ring in the ester side-chain was found to be the major metabolic pathway, and ester bond hydrolysis was a minor metabolic pathway. 6. N-Demethylation of the bridgehead nitrogen was observed only in rat and hamster incubates. 7. Using the method of CNL scanning it was possible to screen different animal microsomal incubates without resorting to any major purification procedures such as h.p.l.c. 8. This scanning method revealed differences between species in the metabolic pathways of cimetropium bromide.