LC/MS study of benzydamine metabolites in bovine liver slices

Benzydamine hydrochloride (BZ) is a nonsteroidal anti-inflammatory drug widely used in human and veterinary therapy. It is metabolized by cattle liver microsomes to benzydamine N-oxide (BZ-NO), Nor-benzydamine (Nor-BZ), and to a more polar metabolite. Its biotransformation in cattle has been studied by using precision-cut liver slices, an alternative in vitro model that is increasingly utilised. Bovine liver slices (Krumdieck Tissue Slicer, 200 m thick, 8 mm diameter) were incubated for 0, 2, 4, 6, 8 and 24 hours with BZ (100, 500 and 1000 M). The incubation mixtures, containing RPMI 1640 W/Glutamax II with 25 mM HEPES (Gibco), and supplements, were maintained at 37°C with 95%O2/5% CO2. The medium obtained from incubated slices was analysed by LC-MS. Nine new metabolites were found besides Nor-BZ and BZ-NO and tentatively identified on the basis of their daughter and grand-daughter ion mass spectra. Three proposed pathways can explain the formation of these metabolites in cattle: benzyl or benzene hydroxylation, dephenylation and conjugation with glucuronic acid to form N+-glucuronides. BZ-NO was the most important derivative and reached at 24 h the highest levels. Previous studies in rats (1) demonstrated that BZ-NO is reduced back to BZ both in vitro and in vivo. Actually, it can act as a reservoir of the parent compound, continually being oxidised and reduced while other metabolites are excreted. References: (1) Kataoka et al. (1973) Chem. Pharm. Bull. 21, 358-365 Work supported by a MURST grant (ex 40% 1998).