title: The biotransformation and urinary excretion of dexamethasone in equine male castrates.
abstract: The pro-drugs of dexamethasone, a potent glucocorticoid, are frequently used as anti-inflammatory steroids in equine veterinary practice. In the present study the biotransformation and urinary excretion of tritium labelled dexamethasone were investigated in cross-bred castrated male horses after therapeutic doses. Between 40-50% of the administered radioactivity was excreted in the urine within 24 h; a further 10% being excreted over the next 3 days. The urinary radioactivity was largely excreted in the unconjugated steroid fraction. In the first 24 h urine sample, 26-36% of the total dose was recovered in the unconjugated fraction, 8-13% in the conjugated fraction and about 5% was unextractable from the urine. The metabolites identified by microchemical transformations and thin-layer chromatography were unchanged dexamethasone, 17-oxodexamethasone, 11-dehydrodexamethasone, 20-dihydrodexamethasone, 6-hydroxydexamethasone and 6-hydroxy-17-oxodexamethasone together accounting for approx 60% of the urinary activity. About 25% of the urinary radioactivity associated with polar metabolites still remains unidentified.
mesh_terms: D000107:Acetylation; D000818:Animals; D001711:Biotransformation; D002855:Chromatography, Thin Layer; D003907:Dexamethasone / Q000378:metabolism* / Q000652:urine; D008401:Gas Chromatography-Mass Spectrometry; D006736:Horses / Q000378:metabolism*; D007273:Injections, Intramuscular; D008297:Male; D009919:Orchiectomy; D010084:Oxidation-Reduction
chemical_list: D003907:Dexamethasone