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-e lution highperformance liquid chromatography coupled with tandem mass spect rometry (LC-MS-MS). The compounds were separated on a Cp Spherisorb 5 mu m 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 metabolit es, and the alpha/beta stereochemistry was resolved. The short (1-2 h) elim ination half-life of methylprednisolone is explained by extensive metabolis m. The overall picture of the metabolic pathways of methylprednisolone is a pparently simple-reduction of the C20 carbonyl group and further oxidation of the C20,C21 side chain (into C21COOH and C20COOH), in competition with o r in addition to oxidation at the C6 position.