Pharmacokinetic and urinary profiling reveals prednisolone/cortisol ratio as a valid biomarker for prednisolone administration

In Europe, synthetic corticosteroids are not allowed in animal breeding fro growth-promoting purposes. Nevertheless, a high prevalence of non-compliant urine samples was recently reported for prednisolone, however, without any indication of unauthorized use. Within this context, 20b-dihydroprednisolone and the prednisolone/cortisol ratio have been suggested as potential tools to discriminate between exogenous and endogenous urinary prednisolone. In this study, the validity of these strategies was verified by investigating the urinary excretion profiles of relevant glucocorticoids in bovines, subjected to either 1) exogenous prednisolone treatment per os (PO), 2) exogenous prednisolone treatment by intra-muscular injection (IM), 3) tetracosactide hexaacetate (ACTH) to induce endogenous prednisolone formation, and 4) animals at slaughter to simulate natural stress conditions. For treatments the exogenous treatments, both growth-promoting and therapeutic prednisolone doses were considered. Bovine urine samples were analysed by liquid chromatography and mass spectrometry.