Identification of metabolites of methylprednisolone in equine urine

Methylprednisolone and three metabolites, 17,21-dihydroxy-6 alpha-methyl-1,4-pregnadiene-3,11,20-trione, 6 alpha-methyl-17,20 beta,21-trihydroxy-1,4-pregnadiene-3,11-dione, and 6 alpha-methyl-11 beta,17,20 beta,21-tetrahydroxy-1,4-pregnadien-3-one were detected in equine urine after intraarticular administration of methylprednisolone acetate. All four compounds were excreted both in the unconjugated form and as glucuronic acid conjugates. They were identified by comparing data obtained from analyses by high performance liquid chromatography, thin-layer chromatography, ultraviolet spectroscopy and gas chromatography/mass spectrometry to those of the synthesized standards. The presence of trace amounts of a fourth metabolite, 6 alpha-methyl-11 beta,17,20 alpha,21-tetrahydroxy-1,4-pregnadien-3-one, was indicated by high performance liquid chromatography but confirmation has not been attained by the other methods.