High-performance Liquid-chromatographic-Atmospheric-pressure Chemical-ionization Ion-trap Mass-spectrometric Identification of Isomeric C6-hydroxy and C20-hydroxy Metabolites of Methylprednisolone in the Urine of Patients Receiving High-dose Pulse Therapy

Fourteen metabolites of methylprednisolone have been analysed by gradient‐elution high‐performance liquid chromatography coupled with tandem mass spectrometry (LC‐MS‐MS). The compounds were separated on a Cp Spherisorb 5 μm ODS column connected to a guard column packed with pellicular reversed phase. The mobile phase was an acetonitrile‐1.0% aqueous acetic acid gradient at a flow rate of 1.5 mL min−1. The analysis gave a complete picture of parent drug, prodrugs and metabolites, and the α/β stereochemistry was resolved. The short (1‐2h) elimination half‐life of methylprednisolone is explained by extensive metabolism. The overall picture of the metabolic pathways of methylprednisolone is apparently simple—reduction of the C20 carbonyl group and further oxidation of the C20, C21 side chain (into C21COOH and C20COOH), in competition with or in addition to oxidation at the C6 position.